Timing of carbohydrate intake for endurance events -
As oral ingestion of very large amounts of glucose i. Yet, evidence for recommending such high ingestion rates i. It could be that athletes whose energy turnover rates during exercise are very high and thus have a high glucose flux to muscle due to increased blood flow proportional to absolute exercise intensity [ 83 ] could benefit from carbohydrate ingestion rates that are higher than currently recommended, but this requires further evaluation.
Additionally, it remains to be established what occurs at intensities in heavy and severe exercise intensity domains, as some evidence indicates that despite higher carbohydrate demands, exogenous carbohydrate oxidation rates do not further increase [ 84 ].
Nonetheless, at present, it cannot be recommended to alter the currently recommended maximal carbohydrate ingestion dose during endurance exercise i. There have been many attempts to increase exogenous carbohydrate oxidation rates by co-ingestion of carbohydrates with other nutrients or nutritional supplements, a topic recently reviewed by Baur and Saunders [ 85 ].
There was no effect from co-ingestion with protein [ 86 ], calcium [ 87 ] or sucralose [ 88 ], use of different glucose polymers [ 89 ] or use of drinks with different osmolality [ 90 ], whereas effects of caffeine co-ingestion yielded mixed results [ 91 , 92 ]. More recently, use of hydrogel-forming carbohydrate drinks and gels has been popularized, and while the majority of studies found this strategy not to affect exogenous carbohydrate oxidation rates [ 95 , 96 ], a recent study found that there could be a positive effect when using solely monosaccharide-based carbohydrate solutions i.
More research is required to better understand a potential utility of the hydrogel. While a vast majority of the studies discussed in the present article are based on interventions conducted in thermoneutral conditions, athletes are commonly required to exercise in extreme environments e. In recent years, advances have been made in understanding how these environmental stressors affect carbohydrate metabolism during exercise [ 98 ] and more work is expected to be undertaken in the upcoming years.
When comparing exercise at the same relative exercise intensity between hypoxia and normoxia, there appear to be no differences in substrate oxidation rates [ ], whereas if the absolute intensity is matched, there is an increase in carbohydrate oxidation rates [ ].
This is met with a reduced ability to oxidize exogenous carbohydrates during exercise at both the same absolute [ ] and relative intensity [ ] It was hypothesized that this is largely explained by reduced peripheral insulin sensitivity because of increased oxidative stress in hypoxia [ ].
Interestingly, altitude acclimation i. Thus, it appears that sufficient pre-exercise carbohydrate intake plays a crucial role in sustaining intense exercise in hypoxia [ ].
Exercise in the heat at the same absolute intensity is accompanied with increased rates of glycogenolysis and thus glycogen utilization in non-heat acclimatized individuals [ , , ]. This effect is somewhat alleviated with heat acclimation [ ], making another argument towards the importance of undertaking heat acclimation before competing in the heat [ ].
Similarly, as with hypoxia, exogenous carbohydrate oxidation rates in non-heat acclimated athletes are reduced under heat stress [ ]. The underlying mechanisms are not yet completely understood. The latter could in turn result in accumulation of glucose within the cell and a reduced glucose gradient between muscle cells and blood [ , ].
Of note is also the fact that under heat stress, athletes are exercising at a higher relative exercise intensity, which drives increased carbohydrate oxidation rates [ 99 , ]. It remains to be explored whether heat acclimation somehow alleviates reductions in exogenous carbohydrate oxidation rates in the heat.
From the applied perspective, currently, the most important solution to circumvent this is combining glucose- and fructose-based carbohydrates so higher exogenous carbohydrate oxidation rates can be achieved than those seen with glucose alone [ ].
The main aim of carbohydrate nutrition in the post-competition period is recovery of liver and muscle glycogen stores. This does not necessarily imply that carbohydrate intake needs to be such that repletion of glycogen stores always needs to be rapid given that the next exercise session might not require full glycogen stores e.
It is believed that for a full repletion of muscle glycogen stores, 24—36 h [ 21 ] are required, whereas for the complete repletion of liver glycogen, 11—25 h are needed [ ].
Current nutritional guidelines recommend athletes ingest moderate to high glycemic index carbohydrates as soon as possible at the rate of 1. However, a close examination of the literature reveals that these guidelines are perhaps too simplistic, especially for elite athletes.
Scrutiny of the evidence for the optimal dosage of carbohydrates to be ingested in the early hours of post-exercise recovery reveals that there is only one study available comparing 1. While it is difficult to compare results between different studies given that different methodological approaches have been used, it appears that there is a good relationship between the dosage and the amount of muscle glycogen resynthesis spanning at least from 0 to 1.
Thus, given that there is also a relationship between training status and the capacity to store muscle glycogen [ 28 ], it could be hypothesized that, absorption permitting, higher ingestion rates would be favorable to elite athletes whose relative proportion of muscle mass is higher. More research is required to elucidate if this is the case.
In addition to this, an emerging topic within the post-exercise recovery period, with an aim to improve functional capabilities of athletes, is the type of carbohydrates ingested in recovery.
Namely, advances have been made on the type of carbohydrates i. While there appears to be no benefit of ingesting multiple types of carbohydrates i. Advancing these data are studies showing that recovery of cycling exercise capacity is greater after ingestion of a combination of glucose-based carbohydrates and fructose as compared to glucose-based carbohydrates only [ , ], likely because of higher carbohydrate availability within both liver and muscle glycogen pools.
It has been hypothesized but not established that combining glucose with both galactose and fructose would result in more rapid replenishment of both glycogen pools [ ]. Interestingly, this strategy did not translate into improved cycling performance [ ].
The results of the latter study are thus surprising. However, a close examination of the results offers a potential explanation and opens new research questions. Namely, two studies [ , ] quantified utilization of in-recovery ingested carbohydrates in the subsequent exercise bout and found an increase in its use, indicating an increased carbohydrate availability.
However, the increase of carbohydrate oxidation rates in the study assessing subsequent cycling performance was such that by the time the cycling time trial was initiated, glycogen stores within the body were likely the same in both conditions.
Thus, more work is required to define the precise scenarios when a functional benefit can be expected; however, there appears to be a uniform observation that in terms of metabolism, ingestion of composite carbohydrates is beneficial. A summary of current knowledge on the effectiveness of different monosaccharide types on repletion of different glycogen depots i.
Based on the current evidence, it could be recommended that athletes seeking to recover glycogen stores as quickly as possible consider ingesting carbohydrates from a combination of glucose-based carbohydrates and fructose to optimally stimulate both liver and muscle glycogen resynthesis.
The same recommendation cannot currently yet be given for galactose as whilst combined galactose-glucose favorably affects liver glycogen synthesis it is currently unknown how effective it is in the replenishment of muscle glycogen stores. Short-term recovery of muscle and liver glycogen stores after exhaustive exercise using different combinations of monosaccharides.
Fructose-glucose carbohydrate mixtures have been demonstrated to be very effective in replenishment of both muscle and liver glycogen stores. On the other hand, while glucose-based carbohydrates cause robust rates of muscle glycogen replenishment, liver glycogen synthesis rates are inferior as compared to a combination of fructose-glucose- and galactose-glucose-based carbohydrates.
No data are currently available for muscle glycogen synthesis rates after ingesting a galactose-glucose mixture. It is hypothesized but not established that combining fructose-galactose-glucose-based carbohydrates would be optimal for post-exercise repletion of both glycogen pools. CHO carbohydrate.
Training can be described as undertaking structured workouts with an aim to improve or maintain performance over time by manipulating the structure, intensity, duration and frequency of training sessions [ , , ]. As total energy requirements and, consequently, carbohydrate demands are high in endurance-based sports, it is fair to assume that optimization of carbohydrate intake in these sport disciplines plays an important role.
Early sports nutrition guidelines [ ] advised athletes to both train and compete with high carbohydrate availability, and this approach dominated until , when Hansen and colleagues observed that a reduction in carbohydrate availability before certain training sessions in untrained individuals could potentially enhance training adaptations [ ].
In this study, leg kicking exercise training was performed in a week-long training study. Each leg was subjected to a different treatment. Muscle biopsy analysis also showed more positive metabolic adaptations hydroxy acyl-CoA dehydrogenase [HAD] and citrate synthase [CS] activity in the leg training with reduced muscle glycogen stores.
While very attractive, the strategy was found to be effective in untrained individuals, and more work was required to see if similar findings could be observed in already trained individuals. As a result, this study was a landmark study paving the way for further investigations into whether different approaches to nutrient availability in trained athletes are beneficial based on different goals: training adaptation or competition performance.
In addition to carbohydrate availability manipulations to influence training adaptations, the concept of training the gut also needs to be considered to become a part of the training process to potentially improve tolerance to high carbohydrate ingestion rates during exercise especially [ , ], as the prevalence of gastrointestinal issues during exercise is large [ , ].
While the concept of training with high carbohydrate intakes to improve tolerance to ingested carbohydrates seems warranted, it remains to be established whether such practice leads to improved absorption of ingested carbohydrates and by what mechanisms or leads to just improved tolerance. Recent evidence from rats indicates that a combination of a high carbohydrate diet and exercise does not result in an increased number of glucose transporters in the intestines [ ], and it could be thus speculated that improved tolerance can occur independently of improved absorption capacity.
Building from the study by Hansen and colleagues, research started to focus on ways to optimize training adaptations and not necessarily optimize performance within these training sessions in trained individuals.
Indeed, studies investigating molecular signaling responses after acute bouts of training with low muscle and liver glycogen stores in trained individuals provided promising results [ 10 , ]. The concept is well described elsewhere [ , ]. Using this approach, some studies demonstrated metabolic benefits, such as reduced reliance on carbohydrates during moderate-intensity exercise [ , ].
However, a recent meta-analysis of nine studies investigating long-term benefits of carbohydrate periodization on performance outcomes suggests that this approach does not always enhance performance in the long term over training with high carbohydrate availability [ ].
Perhaps important to understand when interpreting these data is that large training volumes are accompanied by substantial energy turnover. Even if a training session is initiated with adequate muscle glycogen stores, they will be markedly reduced by the end of it [ 28 ], creating a suitable environment for activation of crucial molecular signaling pathways thought to be responsible for positive adaptations [ ].
One of the fundamental principles of endurance training is achieving sufficient training volume [ , ]. For instance, elite cyclists are reported to cover more than 30, km on the bike in a single year [ ].
Large training volumes are reported in other endurance sports as well [ ]. This provides support for the notion that accumulation of sufficient training volume is of paramount importance among elite endurance athletes. Training with high carbohydrate availability i. Thus, training with low carbohydrate availability should likely be at best viewed as a more time efficient way to train [ , ] rather than the optimal way.
Thus, manipulating carbohydrate availability before and during training sessions could affect molecular responses after exercise bouts. However, focusing solely on activation of pathways such as AMPK could be too reductionist, as it does not account for the recovery that is required after such a session, as, for instance, it is well known that protein breakdown is increased during such sessions [ , ].
In addition to this, recent evidence indicates that the time between two exercise sessions rather than carbohydrate availability is the important modulator of the training responses after the second exercise bout [ , ].
To circumvent this, attempts have been made to rescue the reduction in training capacity by utilization of ingestion of ergogenic aids. In line with this, carbohydrate and caffeine mouth rinsing have been shown to improve high-intensity exercise performance when conducted under a carbohydrate-restricted state [ ].
Whether training adaptation can be enhanced with this approach has not been studied. More recently, building on previous work [ ], the effects of delayed carbohydrate feeding in a glycogen depleted state i.
While performance outcomes were unclear, delayed carbohydrate feeding enabled maintenance of stable blood glucose concentrations without suppressing fat oxidation rates and thus created a favorable metabolic response. Again, whether such an approach leads to longer-term enhancement in training adaptation remains to be seen.
More broadly there is a need to further explore the potential benefits of commencing exercise with low carbohydrate availability to maximize both the metabolic and mechanical i.
Another popular reason for undertaking training with low carbohydrate availability is the notion that such an approach would lead to increases in fat oxidation rates during competition and spare endogenous carbohydrate stores with a limited storage capacity and by doing so improve performance [ 18 , ].
A recent study indicated that the capacity to utilize fat during exercise in an overnight fasted state is best correlated with CS activity [ ], a marker of mitochondrial content [ ] that is itself well correlated with training volume [ ].
More research is required to better understand if training and diet can be structured so that substrate oxidation rates would be altered in favor of fat oxidation without being part of general improvements seen with training per se, and whether this could lead to improvements in endurance performance.
Unfortunately, the prevalence of relative energy deficiency in sport RED-S remains high [ ]. Building on the previous evidence that sufficient carbohydrate intake can ameliorate symptoms of overtraining [ , ], it has recently been proposed that there might be a link between relative RED-S and overtraining and that a common confounding factor is carbohydrate [ 11 ].
Recent data support an important role for dietary carbohydrate, as low carbohydrate, but not low energy availability, affects bone health markers [ ], and deliberately inducing low carbohydrate availability to promote training adaptations and remaining in energy balance by increasing fat intake does not offer any benefits over a combination of energy and carbohydrate deficit—even more, it can impair glycemic regulation [ ].
Whether carbohydrate availability is the crucial part in the development of RED-S remains to be properly elucidated. Collectively, periodizing carbohydrate intake based on the demands of training and especially an upcoming training session currently appears to be the most sensible approach as it 1 allows the execution of the prescribed training program, 2 minimizes the risk of high carbohydrate availability impeding training adaptations and 3 helps minimize the risk for occurrence of RED-S.
A framework for carbohydrate periodization using this concept is depicted in Fig. Framework for carbohydrate periodization based on the demands of the upcoming exercise session.
Exercise intensity domain selection refers to the highest intensity attained during the exercise session. The exact carbohydrate requirements are to be personalized based on the expected energy demands of each exercise session. CHO carbohydrates, CP critical power, LT1 lactate threshold 1, LT2 lactate threshold 2, MLSS maximal lactate steady state.
While provision of exact recommendations for carbohydrate intake before and during exercise forms part of sports nutrition recommendations provided elsewhere [ 1 , 2 ], we believe that interindividual differences in energy and thus carbohydrate requirements are such that optimization of carbohydrate intake should be personalized based on the demands and the goals of the exercise session one is preparing feeding for.
For instance, aggressive provision of carbohydrate intake during exercise deemed beneficial among one population [ 73 ] in another population could lead to unwanted increase in muscle glycogen utilization [ 81 ].
In addition to this, even within sports commonly characterized as featuring extreme energy turnover rates, day-to-day differences are such that provision of exact carbohydrate guidelines would be too inaccurate [ 22 , ]. Thus, personalization of carbohydrate intake during exercise is warranted, as described in the next section.
A certain level of personalization of energy and carbohydrate intake has been a standard part of nutritional guidelines for athletes for years [ 1 , 2 , ]. Practitioners and athletes have a wide array of tools available that can help them personalize energy and carbohydrate intake.
For instance, energy turnover for past training sessions and even energy requirements of the upcoming training sessions can relatively easily be predicted in sports where wearables exist to accurately quantify external work performed i.
Assuming fixed exercise efficiency one can then relatively accurately determine energy turnover during exercise. Knowing the relative exercise intensity of a given training session can further advance the understanding of the carbohydrate demands during exercise, as depicted in Fig. As described in Sect.
Thus, it is possible for athletes to predict energy turnover rates during exercise and adjust the carbohydrate intake accordingly. In addition to this, the literature describing the physiological demands of a given sporting discipline can also be very insightful.
For instance, energy turnover using gold-standard techniques has been assessed in many sporting contexts, including football [ ], cycling [ 22 ] and tennis [ ].
By knowing the energy demands, structure and goals of an upcoming training session, one can devise a suitable carbohydrate feeding strategy. Besides making predictions on total energy turnover during exercise, it is useful to establish the rate of glycogen breakdown, as very high-intensity efforts can substantially reduce muscle glycogen content without very high energy turnover rates [ 34 , ], especially as low glycogen availability can negatively affect performance [ 30 ].
Attempts have been made to find ways to non-invasively and cost-effectively measure muscle glycogen concentrations e. These data can be useful for practitioners to determine the relative i.
However, whilst knowledge of exercise demands can help with tailoring, an implicit assumption is that all athletes will respond in a similar manner to an intervention, which may not be the case.
In this respect, despite the present limitations in the practical assessment of muscle glycogen in field settings, gaining more readily accessible information on individual athlete physiological responses could still be of value to achieve higher degrees of personalization than those that current guidelines allow.
Recently, use of continuous glucose monitoring CGM devices has been popularized among endurance athletes, with an aim of personalizing carbohydrate intake around exercise for optimal performance.
Certainly, knowledge of blood glucose profiles has the advantage that specific physiological data are generated from the individual athlete. These devices have a rich history in the field of diabetes treatment, and their utility has clearly been demonstrated [ ].
For a device to be deemed of use and its use recommended to a wider audience, both of the following criteria must be met: 1 the parameter that the device is measuring should have contextual relevance i. While there is no doubt that CGM devices are useful in non-exercise contexts, their utility during exercise per se remains to be clearly established.
Indeed, CGM devices appear to have limited validity during exercise [ , ], and this may be due to the complex nature of blood glucose regulation during varying types and intensities of exercise.
Blood glucose concentrations are a result of glucose uptake by the tissue and glucose appearance i. While it has been known for a long time that hypoglycemia can associate with task failure [ ], its occurrence does not always precede it [ ].
Therefore, further investigative work is required to establish whether differential blood glucose profiles using validated technology during exercise can be identified and be used to individualize carbohydrate intake during exercise. In addition to tracking glycaemia during exercise, tracking it throughout the day could also be proven useful.
A recent study utilizing CGM devices compared daily blood glucose profiles in elite trained athletes with those in a sedentary population and discovered large discrepancies in blood glucose concentrations throughout the day between both groups [ ].
Elite athletes spent more time in hyper- and hypoglycemia as compared to sedentary controls, giving an appearance that glycemic control might be impaired.
While periods of hyperglycemia are expected due to post-exercise high carbohydrate intakes, observations of hypoglycemia occurring especially at night during sleep were somewhat surprising.
This knowledge can then be used to potentially individualize strategies to counter these episodes of impaired glycemic control in real time. While utilization of CGM devices during exercise to guide carbohydrate intake during exercise cannot be presently advised, athletes could individualize carbohydrate ingestion rates during exercise by establishing their highest exogenous carbohydrate oxidation rates [ 25 ].
To do this, one requires the ability to know carbon isotope enrichments of the ingested carbohydrates and in expired carbon dioxide. For example, advances have been made in methodology to easier quantify stable carbon isotope abundance in expired air [ ], a methodology currently used for quantification of exogenous carbohydrate oxidation rates [ 25 ].
Thus, this approach could be spun off from research and be used in practice as well to identify carbohydrate intake rate and carbohydrate compositions that optimize exogenous carbohydrate oxidation in individual athletes.
Finally, most research to date has investigated carbohydrate intake in a healthy male population, and thus current carbohydrate guidelines are founded on this evidence.
Despite decades of intense carbohydrate research within the field of sports nutrition, new knowledge continues to be generated with the potential to inform practice. In this article, we have highlighted recent observations that provide a more contemporary understanding of the role of carbohydrate nutrition for athletes.
For example, our article suggests a stronger emphasis be placed on scaling carbohydrate intake before competition to the demands of that subsequent activity, with particular attention paid to the effects of concomitant exercise during the preparatory period.
At high ingestion rates during exercise i. Furthermore, short-term recovery may be optimized by combining glucose-fructose to target both liver and muscle glycogen synthesis simultaneously.
Finally, there has been substantial investigation into the role of commencing selected exercise sessions with reduced carbohydrate availability to provide a beneficial stimulus for training adaptation.
The abovementioned suggestions are designed to build on the wealth of knowledge and recommendations already established for athletes. Nonetheless, what this review has also revealed is that gaps in our current understanding of carbohydrate nutrition and metabolism in relation to exercise performance remain.
Some remaining research questions arising from the present article are presented in Table 1. Answering these research questions could allow continued advancement and refinement of carbohydrate intake guidelines and, by doing that, further increase the possibility of positively impacting athletic performance.
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. Article Google Scholar. Thomas DT, Erdman KA, Burke LM. Nutrition and athletic performance. Med Sci Sports Exerc. Evolution of food provision to athletes at the summer Olympic Games.
Nutr Rev. Accessed 4 Dec Krogh A, Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J. Bergstrom J, Hultman E.
A study of glycogen metabolism in man. J Clin Lab Invest. Katz A. A century of exercise physiology: key concepts in regulation of glycogen metabolism in skeletal muscle. Eur J Appl Physiol. Noakes TD. What is the evidence that dietary macronutrient composition influences exercise performance?
A narrative review. Article CAS Google Scholar. Burke LM, Hawley JA, Jeukendrup AE, Morton JP, Stellingwerff T, Maughan RJ. Toward a common understanding of diet-exercise strategies to manipulate fuel availability for training and competition preparation in endurance sport.
Int J Sport Nutr Exerc Metab. Burke LM, Hawley JA. Bartlett JD, Hawley JA, Morton JP. Carbohydrate availability and exercise training adaptation: too much of a good thing?
Eur J Sport Sci. Stellingwerff T, Heikura IA, Meeusen R, Bermon S, Seiler S, Mountjoy ML, et al. Overtraining syndrome OTS and relative energy deficiency in sport RED-S : shared pathways, symptoms and complexities.
Sports Med. Parolin ML, Chesley A, Matsos MP, Spriet LL, Jones NL, Heigenhauser GJF. Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise. Am J Physiol Endocrinol Metab. Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, et al.
Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am J Physiol-Endocrinol Metab. Romijn JA, Coyle EF, Sidossis LS, Gastaldelli A, Horowitz JF, Endert E, et al.
Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. van Loon LJC, Greenhaff PL, Constantin-Teodosiu D, Saris WH, Wagenmakers AJM.
The effects of increasing exercise intensity on muscle fuel utilisation in humans. J Physiol. Leckey JJ, Burke LM, Morton JP, Hawley JA. Altering fatty acid availability does not impair prolonged, continuous running to fatigue: evidence for carbohydrate dependence.
J Appl Physiol. Hawley JA, Leckey JJ. Carbohydrate dependence during prolonged, intense endurance exercise. Hetlelid KJ, Plews DJ, Herold E, Laursen PB, Seiler S. Rethinking the role of fat oxidation: substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners.
BMJ Open Sport Exerc Med. Jeukendrup AE, Wallis GA. Measurement of substrate oxidation during exercise by means of gas exchange measurements. Int J Sports Med Suppl. Gonzalez JT, Fuchs CJ, Betts JA, van Loon LJC. Liver glycogen metabolism during and after prolonged endurance-type exercise.
Burke LM, van Loon LJC, Hawley JA. Postexercise muscle glycogen resynthesis in humans. Plasqui G, Rietjens G, Lambriks L, Wouters L, Saris WHM. Sjödin AM, Andersson AB, Högberg JM, Westerterp KR.
Energy balance in cross-country skiers: a study using doubly labeled water. Accessed 30 Nov Hawley JA, Schabort EJ, Noakes TD, Dennis SC. Carbohydrate-loading and exercise performance. An update. Accessed 2 Aug Jeukendrup AE, Jentjens R. Oxidation of carbohydrate feedings during prolonged exercise.
Accessed 13 Oct Burke LM. Bergström J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and physical performance. Acta Physiol Scand. Areta JL, Hopkins WG.
Skeletal muscle glycogen content at rest and during endurance exercise in humans: a meta-analysis. Jensen R, Ørtenblad N, Stausholm MH, Skjærbæk MC, Larsen DN, Hansen M, et al. Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men.
Vigh-Larsen JF, Ørtenblad N, Spriet LL, Overgaard K, Mohr M. Muscle glycogen metabolism and high-intensity exercise performance: a narrative review.
Nielsen J, Cheng AJ, Ørtenblad N, Westerblad H. Hawley JA, Schabort E, Noakes TD, Dennis SC. Carbohydrate-loading and exercise performance an update. McInerney P, Lessard SJ, Burke LM, Coffey VG, lo Giudice SL, Southgate RJ, et al.
Failure to repeatedly supercompensate muscle glycogen stores in highly trained men. Accessed 2 May Barnett C, Carey M, Proietto J, Cerin E, Febbraio MA, Jenkins D.
Muscle metabolism during sprint exercise in man: Influence of sprint training. J Sci Med Sport. Gollnick PD, Piehl K, Saltin B. Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates.
Sherman WM, Costill DL, Fink WJ, Miller JM. Effect of exercise-diet manipulation on muscle glycogen and its subsequent utilization during performance. Int J Sports Med. Variation in total body water with muscle glycogen changes in man. Acta Physiol Scandi.
Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr. Weyand PG, Davis JA. Running performance has a structural basis. J Exp Biol. Faria EW, Parker DL, Faria IE.
The science of cycling factors affecting performance-part 2. Nilsson LH, Hultman E. Liver glycogen in man—the effect of total starvation or a carbohydrate-poor diet followed by carbohydrate refeeding.
Scand J Clin Lab Investig. Iwayama K, Tanabe Y, Tanji F, Ohnishi T, Takahashi H. Diurnal variations in muscle and liver glycogen differ depending on the timing of exercise. J Physiol Sci. Décombaz J, Jentjens R, Ith M, Scheurer E, Buehler T, Jeukendrup AE, et al.
Fructose and galactose enhance postexercise human liver glycogen synthesis. Liver and muscle glycogen repletion using 13C magnetic resonance spectroscopy following ingestion of maltodextrin, galactose, protein and amino acids.
Br J Nutr. Fuchs CJ, Gonzalez JT, Beelen M, Cermak NM, Smith FE, Thelwall PE, et al. Sucrose ingestion after exhaustive exercise accelerates liver, but not muscle glycogen repletion compared with glucose ingestion in trained athletes.
Podlogar T, Cirnski S, Bokal Š, Verdel N, Gonzalez J. Addition of fructose to a carbohydrate-rich breakfast improves cycling endurance capacity in trained cyclists.
Jeukendrup AE, Killer SC. The myths surrounding pre-exercise carbohydrate feeding. Ann Nutr Metab. Stellingwerff T, Cox GR. Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Appl Physiol Nutr Metab Physiologie appliquee, nutrition et metabolisme.
Carter JM, Jeukendrup AE, Jones DA. The effect of carbohydrate mouth rinse on 1-h cycle time trial performance. Carter JM, Jeukendrup AE, Mann CH, Jones DA. The effect of glucose infusion on glucose kinetics during a 1-h time trial. Chambers ES, Bridge MW, Jones DA. Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity.
Jeukendrup AE, Moseley L, Mainwaring GI, Samuels S, Perry S, Mann CH. Exogenous carbohydrate oxidation during ultraendurance exercise. J Appl Physiol Accessed 18 Nov Coyle EF, Hagberg JM, Hurley BF, Martin WH, Ehsani AA, Holloszy JO. Carbohydrate feeding during prolonged strenuous exercise can delay fatigue.
Coyle EF, Coggan AR, Hemmert MK, Ivy JL. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate.
Jeukendrup AE, Wagenmakers AJM, Stegen J, Gijsen AP, Brouns F, Saris WH. Carbohydrate ingestion can completely suppress endogenous glucose production during exercise. Gonzalez JT, Fuchs CJ, Smith FE, Thelwall PE, Taylor R, Stevenson EJ, et al.
Ingestion of glucose or sucrose prevents liver but not muscle glycogen depletion during prolonged endurance-type exercise in trained cyclists.
Tsintzas OK, Williams C, Boobis L, Greenhaff P. Carbohydrate ingestion and glycogen utilization in different muscle fibre types in man. Carbohydrate ingestion and single muscle fiber glycogen metabolism during prolonged running in men.
Fell JM, Hearris MA, Ellis DG, Moran JEP, Jevons EFP, Owens DJ, et al. Carbohydrate improves exercise capacity but does not affect subcellular lipid droplet morphology, AMPK and p53 signalling in human skeletal muscle.
Jeukendrup AE. Further, protocols for carbohydrate loading differ in research and practice. In most practices from our sport teams growing up, carb loading took place one night before the event, whereas research protocols vary, with seven days of carb loading and tapering training sessions gradually reducing the amount of training for hours leading up to the event.
Maybe we should have a week of spaghetti nights instead of one night before to increase glycogen concentrations more effectively! More seriously, conclusions drawn from the research imply carb loading is only one piece of the dietary puzzle that can advance performance for endurance athletes.
So, what are the practical applications for increasing glycogen storage? The recommended dose for higher carbohydrate intake is grams per kilogram of body weight. For example, an athlete who weighs 85kg should consume around grams of carbohydrates.
Consuming high GI foods appears to promote an increase in glycogen stores in athletes. The most important factor for carbohydrate loading is meeting the overall daily individual carbohydrate needs. While carb loading can be an effective strategy to improve your endurance performance, a holistic approach to carbohydrate availability is most important.
Learn how to improve your athletes' agility. This free course also includes a practical coaching guide to help you design and deliver your own fun and engaging agility sessions.
Brittany is a Scientific Affairs Manager at GNC General Nutrition Centers , reviewing scientific evidence supporting sport nutrition supplements. Learn from a world-class coach how you can improve your athletes' agility.
This course also includes a practical coaching guide to help you to design and deliver your own fun and engaging agility sessions. Our mission is to improve the performance of athletes and teams around the world by simplifying sports science and making it practical.
Pricing FAQs Reviews Free trial. Blog Newsletter Community Podcast Tools. About us Contact us Join our team Privacy policy Terms of use Terms and conditions Disclaimer. Carbohydrate loading for endurance — still a good practice?
Brittany Johnson Brittany is a Scientific Affairs Manager at GNC General Nutrition Centers , reviewing scientific evidence supporting sport nutrition supplements. More content by Brittany. Access our course on Agility for FREE!
Skip to content. Carbohydrates for athletes are an essential part of an effective nutrition strategy. The carbohydrate recommendations for athletes to maximise performance are discussed below:. Are carbs bad for athletes?
No, carbohydrates are the primary energy source for moderate to high-intensity training, so they are extremely valuable for athletes to maximize their energy levels for performance. Do athletes eat a lot of carbs? It will depend on the sport, the level they compete at training volume , dietary preferences, and training goals, but generally, an athlete will eat a high carbohydrate diet.
Why do athletes need more carbs? Carbohydrates are the primary energy source for exercise, so to fuel the high volume of training that athletes do, carbohydrates are needed to support it and maximize their performances.
Why are low carb diets bad for athletes? Carbohydrates are the best source of energy for training. Fats are also an important energy source. However, they are only effective at the low-moderate intensity and are switched off at maximal intensities.
Low carbohydrate diets can therefore impair training performance in athletes. How many carbs can you digest in an hour? During exercise, the body can utilize carbohydrates at a However, highly trained athletes can tolerate larger intakes up to 90g per hour, which improves endurance performance further.
What are the best carbs for athletes? Fruit, vegetables, whole grains, and starches are the most nutrient-dense carbohydrate sources for athletes and make up most of their diet. In addition, simple carbohydrates used in carbohydrate-electrolyte drinks, gels, and energy bars effectively consume the energy they need during training without causing any gastrointestinal discomfort.
Which carbohydrates should be avoided? Excessive intakes of processed, sugary carbohydrates such as sugary drinks, sweets, and foods with added sugars are not advised for athletes.
Is Rice a good carbohydrate? Yes, rice is a high-quality carbohydrate staple in Asian cooking. Brown, basmati, and wild rice are excellent choices with a lower glycaemic index and higher nutrient and fibre content. It is also gluten-free. Can you run on a low-carb diet?
Yes, you can. However, after long periods on a low carbohydrate diet may cause severe fatigue in non-ketogenic adapted athletes, drops in energy levels, and impaired performances may be experienced.
What is the role of carbohydrates in post-exercise recovery? Consuming carbohydrates after exercise help to replenish muscle and liver glycogen stores to support subsequent training sessions. Should athletes eat complex carbohydrates? Yes, athletes should eat complex carbohydrates as part of their diet.
Journal of the International Society of Sports Nutrition foor 14 Timing of carbohydrate intake for endurance events, Article number: 33 Cite this article. Metrics details. The International Society caarbohydrate Sports Nutrition ISSN provides an objective and critical review regarding the timing of macronutrients in reference to healthy, exercising adults and in particular highly trained individuals on exercise performance and body composition. The following points summarize the position of the ISSN:. Nutrient timing incorporates the use of methodical planning and eating of whole foods, fortified foods and dietary supplements.Timing of carbohydrate intake for endurance events -
Undertaking intense exercise sessions i. Additionally, the capacity to perform high-intensity sessions relies heavily on activation of carbohydrate metabolic pathways [ 13 ]. While energy for adenosine triphosphate ATP production can be derived both from fats and carbohydrates, it is carbohydrates that are primarily utilized at high exercise intensities [ 14 , 15 ].
Evidence indicates that utilization of carbohydrates and not fats is crucial to sustain the exercise intensities observed in elite athletes [ 16 , 17 ].
However, the importance of an ability to oxidize fats at high intensities should not be discounted [ 18 ], as a valid method to quantify its contribution to ATP production during exercise at high intensities is yet to be established [ 19 ].
It has been known for decades that pre-exercise carbohydrate stores can influence exercise capacity [ 27 ]. The ability to store muscle glycogen increases with improved training status [ 28 ].
While storage capacity is increased in highly trained populations, it appears that at the time of exhaustion, muscle glycogen concentrations are lower in untrained i. Recently, understanding of the underpinning mechanisms responsible for improved exercise capacity with elevated glycogen stores has improved.
It has been demonstrated that glycogen loading increases exercise capacity by sparing of the intra-myofibrillar glycogen pool and that the intra-myofibrillar pool in type I muscle fibers is the best predictor of prolonged exercise capacity [ 29 ].
During high-intensity exercise efforts e. As a result of the plethora of research demonstrating the importance of muscle glycogen availability, strategies have been devised on how to optimally stimulate muscle glycogen synthesis in the days leading up to competition, a strategy also known as carbohydrate or glycogen loading [ 1 , 32 ].
To achieve muscle glycogen loading, athletes are recommended to consume a very high carbohydrate diet i. However, it is common for athletes to undertake an exercise session in this time frame, during which some of the stored glycogen will be used.
In addition, some sports events e. Indeed, evidence indicates that maintaining high muscle glycogen concentration could be difficult in these circumstances [ 33 ]. More research is required to understand how to better sustain glycogen loading over multiple days, but most likely optimized recovery practices and in-race feeding strategies will represent the most effective ways to maintain adequate carbohydrate availability.
In addition to this, more research is required to better understand how, and if it is possible to, affect skeletal muscle glycogen storage localization by diet manipulation, especially when time for carbohydrate ingestion is limited.
A greater understanding of whether different types of carbohydrate affect the storage localization within muscle is also warranted. While muscle glycogen depletion is more commonly associated with prolonged strenuous endurance exercise, even short but intense exercise bouts can result in significant reduction of muscle glycogen content [ 30 , 34 , 35 ].
Thus, one could assume that because of this, glycogen loading would be warranted. However, the evidence is not as conclusive, as glycogen loading before shorter duration events does not always translate into performance improvements [ 30 , 36 ]. For instance, Sherman and colleagues showed that for runners undertaking a half-marathon, glycogen loading was of no benefit to performance [ 36 ].
Based on this, it is not currently recommended to perform glycogen loading for events shorter than 90 min [ 32 ]. This is especially pertinent for sports where increased BM could significantly hinder performance by reducing sustainable relative exercise intensity e.
However, it is important to discern between functional BM i. Whether liver glycogen stores can also be super compensated remains to be established, as currently there is no clear evidence that this is possible [ 20 ]. Varying carbohydrate intake does indeed change fasting liver glycogen concentrations [ 41 ], and this shows that sufficient carbohydrate intake is required to start an exercise session with normal liver glycogen stores.
However, whether glycogen stores could be increased to higher-than-normal levels remains to be established. It is often overlooked that if competition is to be performed in the morning after an overnight fast or any period of prolonged fasting , liver glycogen stores may be compromised.
Namely, in the postabsorptive phase e. On the contrary, muscle glycogen stores are typically not affected by an overnight fasting period [ 42 ].
As numerous competitions start in the morning, it is pertinent that the meals after overnight fast are designed so that there is a focus on liver glycogen repletion.
While this has not been directly assessed, it could be speculated that providing athletes with a mix of different types of monosaccharides would be beneficial. This suggestion is based on previous observations that combining glucose-based carbohydrates with either fructose or galactose offer benefits on liver glycogen synthesis over glucose-based carbohydrates only [ 43 , 44 , 45 ].
Indeed, a recent study found improved exercise capacity with a breakfast consisting of fructose-glucose-based carbohydrates as compared to glucose-based carbohydrates only [ 46 ]. This would advance practical advice not only from the perspective of optimization of liver glycogen levels, but also from the perspective of preventing consequences of rebound hypoglycemia, which can occur in some athletes when exercise bouts are initiated close to a meal [ 47 ].
Current nutritional guidelines for athletes advise to consume carbohydrates during exercise at different rates and in relation to the duration of exercise bouts, as will be discussed later [ 1 , 2 ].
There are currently two proposed mechanisms of carbohydrate ergogenicity. Firstly, carbohydrates can be sensed in the oral cavity, causing an activation of certain brain regions, leading to stimulation of the central nervous system, as shown by improved performance by carbohydrate mouth rinsing [ 49 , 50 , 51 ].
Secondly, and most importantly, carbohydrates provide an additional fuel source for ATP formation during exercise. Carbohydrate ingestion during exercise maintains stable blood glucose levels over long exercise sessions [ 52 ] and maintains carbohydrate oxidation rates despite declining muscle glycogen stores so that ingested carbohydrates substitute endogenous carbohydrate stores [ 53 , 54 ].
In addition to this, exogenous carbohydrates can spare or even completely suppress liver glycogen breakdown [ 55 , 56 ]. While some studies have found sparing of muscle glycogen with carbohydrate supplementation during exercise [ 57 , 58 ], most of the studies assessing whole muscle glycogen utilization did not see this effect [ 28 ] and a recently published study that evaluated different carbohydrate ingestion rates during cycling exercise did not observe sparing of muscle glycogen in a muscle fiber type-specific manner either [ 59 ].
However, more recent evidence indicating the importance of compartmentalized glycogen metabolism to muscle function opens new avenues for investigating the mechanistic basis of carbohydrate feeding during exercise [ 29 ]. Galactose has typically not been recommended to be ingested during exercise due to a belief that it is not as readily oxidized [ 61 , 62 ].
However, recent evidence demonstrates that at moderate dosages i. It remains to be demonstrated directly, but these data indicate that oxidation of galactose during exercise is not limited when provided as lactose at moderate ingestion rates.
Thus, lactose as a source of galactose and glucose can be ingested as an alternative carbohydrate source during exercise, at least in lactose-tolerant individuals.
It is believed that at this ingestion rate, the sodium-glucose linked transporters SGLT1 in the small intestine become saturated [ 25 ]. This notion is based on the observations that when fructose, whose absorption from the small intestine utilizes a different transporter i. As a result of this, athletes are recommended to ingest mixtures of glucose- and fructose-based carbohydrates when training or competition is longer than 2.
Most studies investigating combined ingestion of glucose-based carbohydrates and fructose utilized a glucose:fructose ratio, and this has since become a standard recommendation [ 60 ]. However, a closer examination of the literature reveals that a ratio closer to unity i.
Thus, it could be recommended that composite glucose- and fructose-based carbohydrates in a ratio close to unity are ingested irrespective of exercise duration. The suggestion that glucose-fructose mixtures be recommended over single transportable carbohydrates even when exercise duration lies within 1—2.
Most studies to date investigating exogenous carbohydrate oxidation rates have been performed on moderately to highly trained athletes, but not in elite athletes whose absolute energy demands can be vastly higher.
However, endogenous carbohydrate oxidation was not further spared by the higher carbohydrate dose, and thus whether there would be an additional performance benefit requires clarification. Current evidence indicates that glucose delivery to the active tissue i.
Bypassing intestinal absorption by infusing glucose and maintaining glycaemia did not result in higher exogenous glucose oxidation rates [ 74 ], whereas infusing glucose to maintain hyperglycemia i.
This occurred without a reduction in muscle glycogen use, but rather with suppression of fat oxidation rates. As oral ingestion of very large amounts of glucose i. Yet, evidence for recommending such high ingestion rates i.
It could be that athletes whose energy turnover rates during exercise are very high and thus have a high glucose flux to muscle due to increased blood flow proportional to absolute exercise intensity [ 83 ] could benefit from carbohydrate ingestion rates that are higher than currently recommended, but this requires further evaluation.
Additionally, it remains to be established what occurs at intensities in heavy and severe exercise intensity domains, as some evidence indicates that despite higher carbohydrate demands, exogenous carbohydrate oxidation rates do not further increase [ 84 ].
Nonetheless, at present, it cannot be recommended to alter the currently recommended maximal carbohydrate ingestion dose during endurance exercise i.
There have been many attempts to increase exogenous carbohydrate oxidation rates by co-ingestion of carbohydrates with other nutrients or nutritional supplements, a topic recently reviewed by Baur and Saunders [ 85 ].
There was no effect from co-ingestion with protein [ 86 ], calcium [ 87 ] or sucralose [ 88 ], use of different glucose polymers [ 89 ] or use of drinks with different osmolality [ 90 ], whereas effects of caffeine co-ingestion yielded mixed results [ 91 , 92 ].
More recently, use of hydrogel-forming carbohydrate drinks and gels has been popularized, and while the majority of studies found this strategy not to affect exogenous carbohydrate oxidation rates [ 95 , 96 ], a recent study found that there could be a positive effect when using solely monosaccharide-based carbohydrate solutions i.
More research is required to better understand a potential utility of the hydrogel. While a vast majority of the studies discussed in the present article are based on interventions conducted in thermoneutral conditions, athletes are commonly required to exercise in extreme environments e.
In recent years, advances have been made in understanding how these environmental stressors affect carbohydrate metabolism during exercise [ 98 ] and more work is expected to be undertaken in the upcoming years.
When comparing exercise at the same relative exercise intensity between hypoxia and normoxia, there appear to be no differences in substrate oxidation rates [ ], whereas if the absolute intensity is matched, there is an increase in carbohydrate oxidation rates [ ].
This is met with a reduced ability to oxidize exogenous carbohydrates during exercise at both the same absolute [ ] and relative intensity [ ] It was hypothesized that this is largely explained by reduced peripheral insulin sensitivity because of increased oxidative stress in hypoxia [ ]. Interestingly, altitude acclimation i.
Thus, it appears that sufficient pre-exercise carbohydrate intake plays a crucial role in sustaining intense exercise in hypoxia [ ]. Exercise in the heat at the same absolute intensity is accompanied with increased rates of glycogenolysis and thus glycogen utilization in non-heat acclimatized individuals [ , , ].
This effect is somewhat alleviated with heat acclimation [ ], making another argument towards the importance of undertaking heat acclimation before competing in the heat [ ]. Similarly, as with hypoxia, exogenous carbohydrate oxidation rates in non-heat acclimated athletes are reduced under heat stress [ ].
The underlying mechanisms are not yet completely understood. The latter could in turn result in accumulation of glucose within the cell and a reduced glucose gradient between muscle cells and blood [ , ]. Of note is also the fact that under heat stress, athletes are exercising at a higher relative exercise intensity, which drives increased carbohydrate oxidation rates [ 99 , ].
It remains to be explored whether heat acclimation somehow alleviates reductions in exogenous carbohydrate oxidation rates in the heat.
From the applied perspective, currently, the most important solution to circumvent this is combining glucose- and fructose-based carbohydrates so higher exogenous carbohydrate oxidation rates can be achieved than those seen with glucose alone [ ].
The main aim of carbohydrate nutrition in the post-competition period is recovery of liver and muscle glycogen stores. This does not necessarily imply that carbohydrate intake needs to be such that repletion of glycogen stores always needs to be rapid given that the next exercise session might not require full glycogen stores e.
It is believed that for a full repletion of muscle glycogen stores, 24—36 h [ 21 ] are required, whereas for the complete repletion of liver glycogen, 11—25 h are needed [ ]. Current nutritional guidelines recommend athletes ingest moderate to high glycemic index carbohydrates as soon as possible at the rate of 1.
However, a close examination of the literature reveals that these guidelines are perhaps too simplistic, especially for elite athletes. Scrutiny of the evidence for the optimal dosage of carbohydrates to be ingested in the early hours of post-exercise recovery reveals that there is only one study available comparing 1.
While it is difficult to compare results between different studies given that different methodological approaches have been used, it appears that there is a good relationship between the dosage and the amount of muscle glycogen resynthesis spanning at least from 0 to 1.
Thus, given that there is also a relationship between training status and the capacity to store muscle glycogen [ 28 ], it could be hypothesized that, absorption permitting, higher ingestion rates would be favorable to elite athletes whose relative proportion of muscle mass is higher.
More research is required to elucidate if this is the case. In addition to this, an emerging topic within the post-exercise recovery period, with an aim to improve functional capabilities of athletes, is the type of carbohydrates ingested in recovery.
Namely, advances have been made on the type of carbohydrates i. While there appears to be no benefit of ingesting multiple types of carbohydrates i. Advancing these data are studies showing that recovery of cycling exercise capacity is greater after ingestion of a combination of glucose-based carbohydrates and fructose as compared to glucose-based carbohydrates only [ , ], likely because of higher carbohydrate availability within both liver and muscle glycogen pools.
It has been hypothesized but not established that combining glucose with both galactose and fructose would result in more rapid replenishment of both glycogen pools [ ]. Interestingly, this strategy did not translate into improved cycling performance [ ].
The results of the latter study are thus surprising. However, a close examination of the results offers a potential explanation and opens new research questions. Namely, two studies [ , ] quantified utilization of in-recovery ingested carbohydrates in the subsequent exercise bout and found an increase in its use, indicating an increased carbohydrate availability.
However, the increase of carbohydrate oxidation rates in the study assessing subsequent cycling performance was such that by the time the cycling time trial was initiated, glycogen stores within the body were likely the same in both conditions.
Thus, more work is required to define the precise scenarios when a functional benefit can be expected; however, there appears to be a uniform observation that in terms of metabolism, ingestion of composite carbohydrates is beneficial.
A summary of current knowledge on the effectiveness of different monosaccharide types on repletion of different glycogen depots i. Based on the current evidence, it could be recommended that athletes seeking to recover glycogen stores as quickly as possible consider ingesting carbohydrates from a combination of glucose-based carbohydrates and fructose to optimally stimulate both liver and muscle glycogen resynthesis.
The same recommendation cannot currently yet be given for galactose as whilst combined galactose-glucose favorably affects liver glycogen synthesis it is currently unknown how effective it is in the replenishment of muscle glycogen stores. Short-term recovery of muscle and liver glycogen stores after exhaustive exercise using different combinations of monosaccharides.
Fructose-glucose carbohydrate mixtures have been demonstrated to be very effective in replenishment of both muscle and liver glycogen stores.
On the other hand, while glucose-based carbohydrates cause robust rates of muscle glycogen replenishment, liver glycogen synthesis rates are inferior as compared to a combination of fructose-glucose- and galactose-glucose-based carbohydrates.
No data are currently available for muscle glycogen synthesis rates after ingesting a galactose-glucose mixture. It is hypothesized but not established that combining fructose-galactose-glucose-based carbohydrates would be optimal for post-exercise repletion of both glycogen pools.
CHO carbohydrate. Training can be described as undertaking structured workouts with an aim to improve or maintain performance over time by manipulating the structure, intensity, duration and frequency of training sessions [ , , ].
As total energy requirements and, consequently, carbohydrate demands are high in endurance-based sports, it is fair to assume that optimization of carbohydrate intake in these sport disciplines plays an important role.
Early sports nutrition guidelines [ ] advised athletes to both train and compete with high carbohydrate availability, and this approach dominated until , when Hansen and colleagues observed that a reduction in carbohydrate availability before certain training sessions in untrained individuals could potentially enhance training adaptations [ ].
In this study, leg kicking exercise training was performed in a week-long training study. Each leg was subjected to a different treatment. Muscle biopsy analysis also showed more positive metabolic adaptations hydroxy acyl-CoA dehydrogenase [HAD] and citrate synthase [CS] activity in the leg training with reduced muscle glycogen stores.
While very attractive, the strategy was found to be effective in untrained individuals, and more work was required to see if similar findings could be observed in already trained individuals.
As a result, this study was a landmark study paving the way for further investigations into whether different approaches to nutrient availability in trained athletes are beneficial based on different goals: training adaptation or competition performance.
In addition to carbohydrate availability manipulations to influence training adaptations, the concept of training the gut also needs to be considered to become a part of the training process to potentially improve tolerance to high carbohydrate ingestion rates during exercise especially [ , ], as the prevalence of gastrointestinal issues during exercise is large [ , ].
While the concept of training with high carbohydrate intakes to improve tolerance to ingested carbohydrates seems warranted, it remains to be established whether such practice leads to improved absorption of ingested carbohydrates and by what mechanisms or leads to just improved tolerance.
Recent evidence from rats indicates that a combination of a high carbohydrate diet and exercise does not result in an increased number of glucose transporters in the intestines [ ], and it could be thus speculated that improved tolerance can occur independently of improved absorption capacity.
Building from the study by Hansen and colleagues, research started to focus on ways to optimize training adaptations and not necessarily optimize performance within these training sessions in trained individuals.
Indeed, studies investigating molecular signaling responses after acute bouts of training with low muscle and liver glycogen stores in trained individuals provided promising results [ 10 , ]. The concept is well described elsewhere [ , ]. Using this approach, some studies demonstrated metabolic benefits, such as reduced reliance on carbohydrates during moderate-intensity exercise [ , ].
However, a recent meta-analysis of nine studies investigating long-term benefits of carbohydrate periodization on performance outcomes suggests that this approach does not always enhance performance in the long term over training with high carbohydrate availability [ ]. Perhaps important to understand when interpreting these data is that large training volumes are accompanied by substantial energy turnover.
Even if a training session is initiated with adequate muscle glycogen stores, they will be markedly reduced by the end of it [ 28 ], creating a suitable environment for activation of crucial molecular signaling pathways thought to be responsible for positive adaptations [ ].
One of the fundamental principles of endurance training is achieving sufficient training volume [ , ]. For instance, elite cyclists are reported to cover more than 30, km on the bike in a single year [ ]. Large training volumes are reported in other endurance sports as well [ ].
This provides support for the notion that accumulation of sufficient training volume is of paramount importance among elite endurance athletes. Training with high carbohydrate availability i. Thus, training with low carbohydrate availability should likely be at best viewed as a more time efficient way to train [ , ] rather than the optimal way.
Thus, manipulating carbohydrate availability before and during training sessions could affect molecular responses after exercise bouts. However, focusing solely on activation of pathways such as AMPK could be too reductionist, as it does not account for the recovery that is required after such a session, as, for instance, it is well known that protein breakdown is increased during such sessions [ , ].
In addition to this, recent evidence indicates that the time between two exercise sessions rather than carbohydrate availability is the important modulator of the training responses after the second exercise bout [ , ]. To circumvent this, attempts have been made to rescue the reduction in training capacity by utilization of ingestion of ergogenic aids.
In line with this, carbohydrate and caffeine mouth rinsing have been shown to improve high-intensity exercise performance when conducted under a carbohydrate-restricted state [ ].
Whether training adaptation can be enhanced with this approach has not been studied. More recently, building on previous work [ ], the effects of delayed carbohydrate feeding in a glycogen depleted state i. While performance outcomes were unclear, delayed carbohydrate feeding enabled maintenance of stable blood glucose concentrations without suppressing fat oxidation rates and thus created a favorable metabolic response.
Again, whether such an approach leads to longer-term enhancement in training adaptation remains to be seen. More broadly there is a need to further explore the potential benefits of commencing exercise with low carbohydrate availability to maximize both the metabolic and mechanical i. Another popular reason for undertaking training with low carbohydrate availability is the notion that such an approach would lead to increases in fat oxidation rates during competition and spare endogenous carbohydrate stores with a limited storage capacity and by doing so improve performance [ 18 , ].
A recent study indicated that the capacity to utilize fat during exercise in an overnight fasted state is best correlated with CS activity [ ], a marker of mitochondrial content [ ] that is itself well correlated with training volume [ ].
More research is required to better understand if training and diet can be structured so that substrate oxidation rates would be altered in favor of fat oxidation without being part of general improvements seen with training per se, and whether this could lead to improvements in endurance performance.
Unfortunately, the prevalence of relative energy deficiency in sport RED-S remains high [ ]. Building on the previous evidence that sufficient carbohydrate intake can ameliorate symptoms of overtraining [ , ], it has recently been proposed that there might be a link between relative RED-S and overtraining and that a common confounding factor is carbohydrate [ 11 ].
Recent data support an important role for dietary carbohydrate, as low carbohydrate, but not low energy availability, affects bone health markers [ ], and deliberately inducing low carbohydrate availability to promote training adaptations and remaining in energy balance by increasing fat intake does not offer any benefits over a combination of energy and carbohydrate deficit—even more, it can impair glycemic regulation [ ].
Whether carbohydrate availability is the crucial part in the development of RED-S remains to be properly elucidated. Collectively, periodizing carbohydrate intake based on the demands of training and especially an upcoming training session currently appears to be the most sensible approach as it 1 allows the execution of the prescribed training program, 2 minimizes the risk of high carbohydrate availability impeding training adaptations and 3 helps minimize the risk for occurrence of RED-S.
A framework for carbohydrate periodization using this concept is depicted in Fig. Framework for carbohydrate periodization based on the demands of the upcoming exercise session. Exercise intensity domain selection refers to the highest intensity attained during the exercise session.
The exact carbohydrate requirements are to be personalized based on the expected energy demands of each exercise session. CHO carbohydrates, CP critical power, LT1 lactate threshold 1, LT2 lactate threshold 2, MLSS maximal lactate steady state.
While provision of exact recommendations for carbohydrate intake before and during exercise forms part of sports nutrition recommendations provided elsewhere [ 1 , 2 ], we believe that interindividual differences in energy and thus carbohydrate requirements are such that optimization of carbohydrate intake should be personalized based on the demands and the goals of the exercise session one is preparing feeding for.
For instance, aggressive provision of carbohydrate intake during exercise deemed beneficial among one population [ 73 ] in another population could lead to unwanted increase in muscle glycogen utilization [ 81 ].
In addition to this, even within sports commonly characterized as featuring extreme energy turnover rates, day-to-day differences are such that provision of exact carbohydrate guidelines would be too inaccurate [ 22 , ].
Thus, personalization of carbohydrate intake during exercise is warranted, as described in the next section. A certain level of personalization of energy and carbohydrate intake has been a standard part of nutritional guidelines for athletes for years [ 1 , 2 , ].
Practitioners and athletes have a wide array of tools available that can help them personalize energy and carbohydrate intake.
For instance, energy turnover for past training sessions and even energy requirements of the upcoming training sessions can relatively easily be predicted in sports where wearables exist to accurately quantify external work performed i. Assuming fixed exercise efficiency one can then relatively accurately determine energy turnover during exercise.
Knowing the relative exercise intensity of a given training session can further advance the understanding of the carbohydrate demands during exercise, as depicted in Fig. As described in Sect. Thus, it is possible for athletes to predict energy turnover rates during exercise and adjust the carbohydrate intake accordingly.
In addition to this, the literature describing the physiological demands of a given sporting discipline can also be very insightful. For instance, energy turnover using gold-standard techniques has been assessed in many sporting contexts, including football [ ], cycling [ 22 ] and tennis [ ].
By knowing the energy demands, structure and goals of an upcoming training session, one can devise a suitable carbohydrate feeding strategy. Besides making predictions on total energy turnover during exercise, it is useful to establish the rate of glycogen breakdown, as very high-intensity efforts can substantially reduce muscle glycogen content without very high energy turnover rates [ 34 , ], especially as low glycogen availability can negatively affect performance [ 30 ].
Attempts have been made to find ways to non-invasively and cost-effectively measure muscle glycogen concentrations e. These data can be useful for practitioners to determine the relative i.
However, whilst knowledge of exercise demands can help with tailoring, an implicit assumption is that all athletes will respond in a similar manner to an intervention, which may not be the case. In this respect, despite the present limitations in the practical assessment of muscle glycogen in field settings, gaining more readily accessible information on individual athlete physiological responses could still be of value to achieve higher degrees of personalization than those that current guidelines allow.
Recently, use of continuous glucose monitoring CGM devices has been popularized among endurance athletes, with an aim of personalizing carbohydrate intake around exercise for optimal performance.
Certainly, knowledge of blood glucose profiles has the advantage that specific physiological data are generated from the individual athlete. These devices have a rich history in the field of diabetes treatment, and their utility has clearly been demonstrated [ ].
For a device to be deemed of use and its use recommended to a wider audience, both of the following criteria must be met: 1 the parameter that the device is measuring should have contextual relevance i. While there is no doubt that CGM devices are useful in non-exercise contexts, their utility during exercise per se remains to be clearly established.
Indeed, CGM devices appear to have limited validity during exercise [ , ], and this may be due to the complex nature of blood glucose regulation during varying types and intensities of exercise.
Blood glucose concentrations are a result of glucose uptake by the tissue and glucose appearance i. While it has been known for a long time that hypoglycemia can associate with task failure [ ], its occurrence does not always precede it [ ].
Therefore, further investigative work is required to establish whether differential blood glucose profiles using validated technology during exercise can be identified and be used to individualize carbohydrate intake during exercise.
In addition to tracking glycaemia during exercise, tracking it throughout the day could also be proven useful. A recent study utilizing CGM devices compared daily blood glucose profiles in elite trained athletes with those in a sedentary population and discovered large discrepancies in blood glucose concentrations throughout the day between both groups [ ].
Elite athletes spent more time in hyper- and hypoglycemia as compared to sedentary controls, giving an appearance that glycemic control might be impaired. While periods of hyperglycemia are expected due to post-exercise high carbohydrate intakes, observations of hypoglycemia occurring especially at night during sleep were somewhat surprising.
This knowledge can then be used to potentially individualize strategies to counter these episodes of impaired glycemic control in real time. While utilization of CGM devices during exercise to guide carbohydrate intake during exercise cannot be presently advised, athletes could individualize carbohydrate ingestion rates during exercise by establishing their highest exogenous carbohydrate oxidation rates [ 25 ].
To do this, one requires the ability to know carbon isotope enrichments of the ingested carbohydrates and in expired carbon dioxide.
For example, advances have been made in methodology to easier quantify stable carbon isotope abundance in expired air [ ], a methodology currently used for quantification of exogenous carbohydrate oxidation rates [ 25 ].
Thus, this approach could be spun off from research and be used in practice as well to identify carbohydrate intake rate and carbohydrate compositions that optimize exogenous carbohydrate oxidation in individual athletes. Finally, most research to date has investigated carbohydrate intake in a healthy male population, and thus current carbohydrate guidelines are founded on this evidence.
Despite decades of intense carbohydrate research within the field of sports nutrition, new knowledge continues to be generated with the potential to inform practice. In this article, we have highlighted recent observations that provide a more contemporary understanding of the role of carbohydrate nutrition for athletes.
For example, our article suggests a stronger emphasis be placed on scaling carbohydrate intake before competition to the demands of that subsequent activity, with particular attention paid to the effects of concomitant exercise during the preparatory period.
At high ingestion rates during exercise i. Furthermore, short-term recovery may be optimized by combining glucose-fructose to target both liver and muscle glycogen synthesis simultaneously. Finally, there has been substantial investigation into the role of commencing selected exercise sessions with reduced carbohydrate availability to provide a beneficial stimulus for training adaptation.
The abovementioned suggestions are designed to build on the wealth of knowledge and recommendations already established for athletes. Nonetheless, what this review has also revealed is that gaps in our current understanding of carbohydrate nutrition and metabolism in relation to exercise performance remain.
Some remaining research questions arising from the present article are presented in Table 1. Answering these research questions could allow continued advancement and refinement of carbohydrate intake guidelines and, by doing that, further increase the possibility of positively impacting athletic performance.
Burke LM, Hawley JA, Wong SHS, Jeukendrup AE. Carbohydrates for training and competition. J Sports Sci. Article Google Scholar.
Thomas DT, Erdman KA, Burke LM. Nutrition and athletic performance. Med Sci Sports Exerc. Evolution of food provision to athletes at the summer Olympic Games.
Nutr Rev. Accessed 4 Dec Krogh A, Lindhard J. The relative value of fat and carbohydrate as sources of muscular energy. Biochem J. Bergstrom J, Hultman E. A study of glycogen metabolism in man.
J Clin Lab Invest. Katz A. A century of exercise physiology: key concepts in regulation of glycogen metabolism in skeletal muscle. Eur J Appl Physiol. Noakes TD. What is the evidence that dietary macronutrient composition influences exercise performance? A narrative review.
Article CAS Google Scholar. Burke LM, Hawley JA, Jeukendrup AE, Morton JP, Stellingwerff T, Maughan RJ. Toward a common understanding of diet-exercise strategies to manipulate fuel availability for training and competition preparation in endurance sport.
Int J Sport Nutr Exerc Metab. Burke LM, Hawley JA. Bartlett JD, Hawley JA, Morton JP. Carbohydrate availability and exercise training adaptation: too much of a good thing? Eur J Sport Sci. Stellingwerff T, Heikura IA, Meeusen R, Bermon S, Seiler S, Mountjoy ML, et al.
Overtraining syndrome OTS and relative energy deficiency in sport RED-S : shared pathways, symptoms and complexities. Sports Med. Parolin ML, Chesley A, Matsos MP, Spriet LL, Jones NL, Heigenhauser GJF.
Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise. Am J Physiol Endocrinol Metab. Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, et al. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration.
Am J Physiol-Endocrinol Metab. Romijn JA, Coyle EF, Sidossis LS, Gastaldelli A, Horowitz JF, Endert E, et al. Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration.
van Loon LJC, Greenhaff PL, Constantin-Teodosiu D, Saris WH, Wagenmakers AJM. The effects of increasing exercise intensity on muscle fuel utilisation in humans.
J Physiol. Leckey JJ, Burke LM, Morton JP, Hawley JA. Altering fatty acid availability does not impair prolonged, continuous running to fatigue: evidence for carbohydrate dependence. J Appl Physiol. Hawley JA, Leckey JJ. Carbohydrate dependence during prolonged, intense endurance exercise.
Hetlelid KJ, Plews DJ, Herold E, Laursen PB, Seiler S. Rethinking the role of fat oxidation: substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners.
BMJ Open Sport Exerc Med. Jeukendrup AE, Wallis GA. Measurement of substrate oxidation during exercise by means of gas exchange measurements. Int J Sports Med Suppl. Gonzalez JT, Fuchs CJ, Betts JA, van Loon LJC. Liver glycogen metabolism during and after prolonged endurance-type exercise.
Burke LM, van Loon LJC, Hawley JA. Postexercise muscle glycogen resynthesis in humans. Plasqui G, Rietjens G, Lambriks L, Wouters L, Saris WHM. Sjödin AM, Andersson AB, Högberg JM, Westerterp KR. Energy balance in cross-country skiers: a study using doubly labeled water. Accessed 30 Nov Hawley JA, Schabort EJ, Noakes TD, Dennis SC.
Carbohydrate-loading and exercise performance. An update. Accessed 2 Aug Jeukendrup AE, Jentjens R. Oxidation of carbohydrate feedings during prolonged exercise.
Accessed 13 Oct Burke LM. Bergström J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and physical performance. Acta Physiol Scand. Areta JL, Hopkins WG. Skeletal muscle glycogen content at rest and during endurance exercise in humans: a meta-analysis. Jensen R, Ørtenblad N, Stausholm MH, Skjærbæk MC, Larsen DN, Hansen M, et al.
Heterogeneity in subcellular muscle glycogen utilisation during exercise impacts endurance capacity in men. Vigh-Larsen JF, Ørtenblad N, Spriet LL, Overgaard K, Mohr M.
Muscle glycogen metabolism and high-intensity exercise performance: a narrative review. Nielsen J, Cheng AJ, Ørtenblad N, Westerblad H. Hawley JA, Schabort E, Noakes TD, Dennis SC.
Carbohydrate-loading and exercise performance an update. McInerney P, Lessard SJ, Burke LM, Coffey VG, lo Giudice SL, Southgate RJ, et al.
Failure to repeatedly supercompensate muscle glycogen stores in highly trained men. Accessed 2 May Barnett C, Carey M, Proietto J, Cerin E, Febbraio MA, Jenkins D.
Koepsell H. Glucose transporters in the small intestine in health and disease. Pflugers Arch. Miall A, Khoo A, Rauch C, Snipe RJ, Canoes-Costa VL, Gibson PR, Costa RJS.
Two weeks of repetitive gut-challenge reduce exercise-associated gastrointestinal symptoms and malabsorption. Pfeiffer B, Stellingwerf T, Hodgson AB, Randell R, Pottgen K, Res P, Jeukendrup AE.
Nutritional intake and gastrointestinal problems during competitive endurance events. Med Sci Sports Exerc. Rumessen JJ, Gudmand-Hoyer E. Absorption capacity of fructose in healthy adults. Comparison with sucrose and its constituent monosaccharides.
Scow JS, Tavakkolizadeh A, Zheng y, Sarr MG. International Society of Sports Nutrition Position Stand: nutritional considerations for single-stage ultra-marathon training and racing. J Int Soc Sports Nutr. Urdampilleta A, Arriblazaga S, Viribay A, Castaneda-Babarro A, Seco-Calvo J, Mielgo-Ayuso J.
Effects of vs. Viribay A, Arribalzaga S, Mielgo-Ayuso J, Castaneda-Babarro A, Seco-Calvo J, Urdampilleta A. Did you find this post interesting and valuable or was it a waste of your time? If so, leave a comment below and we'll get back to you right away.
You are eligible for free shipping! Check out. Start shopping. Left Right. Search Shop Community Who We Are My Rewards. Account Search Cart. Shop Toggle menu Daily Toggle menu HALO MultiV MultiV-PRO Optygen OptygenHP. PreRace Liquid Shot EFS Drink Mix EFS-PRO High Carb.
Athletes Articles Films. How Many Carbs Should Endurance Athletes Really Consume Per Hour? New Epiphanies Max Out Carb Intakes for Endurance Athletes By Dr. Luke R. Bucci and Jeff Feliciano Introduction One of the most frequent questions we get is: How many carbs do I need to take during my long-duration events, races or training lasting more than three hours?
The Recent Epiphanies Reshaping Carb Intake Carbs used to be so simple — just take in plenty of sugar or glucose or maltodextrin or a combination thereof. Epiphany 1: MTCs Were a Carb Revolution — All About GLUT5 recently renamed SLC2A5 MTCs means Multiple Transportable Carbohydrates, which really gathered steam in the mids and are now the norm.
Epiphany 2: Instant Adaptation Opens Glucose Floodgates Very recently, another research epiphany overturned intestinal dogma by showing that GLUT2 recently renamed SLC2A2 , another transporter for glucose, can rapidly show up on the apical, or inward absorptive side of gut enterocytes — within minutes after ingestion of high glucose loads.
Epiphany 3: Gut Training for Increased Carb Intake Studies have shown that training your gut to accept higher carb intakes during exercise can be accomplished in two weeks. References Alam YH, Kim R, Jang C. Share Facebook Share on Facebook Twitter Share on Twitter Pinterest Pin it.
Left Older Post Back to Articles Newer Post Right. Leave a comment Please note: comments must be approved before they are published. Post comment. Join The Conversation Did you find this post interesting and valuable or was it a waste of your time? Don't have an account? Endurance Nutrition.
Connect With Us. Get the best offers, priority access to new releases, and more! Finding the best solution may involve starting with basic nutrition recommendations. Finding the best diet for endurance is often a trial-and-error process.
As always, keep your scope of practice in mind as a personal trainer—make sure you're cleared to talk about nutrition with clients.
Now, let's dig into the details of dietary needs for endurance. Macronutrients are the basic components of the food we eat. These are carbohydrates, protein, and fat. Eating macros in proper ratios fuel your endurance. Healthy adult eating includes ratios of:.
Adjust these ratios based on the goal of the physical activity. For example, an endurance athlete would increase their carb percentage to improve muscle glycogen stores. A strength athlete would consume a higher protein intake.
This would better support building more muscle mass. Carbs come in different forms. Two to know are simple and complex carbs. Simple carbs , also known as simple sugars, have one to two sugar molecules. These include glucose, dextrose, or fructose.
Simple carbs break down quickly in the body. Foods with simple sugars include fruits, milk, vegetables, table sugar, candy, and soft drinks. They supply energy but lack fiber, vitamins, and other key nutrients. Complex carbs have three or more sugar molecules. You'll find these in foods like beans, whole grains, whole-wheat pasta, potatoes, corn, and legumes.
So, which kind of carbohydrate should you consume? Most carbs should come from complex sources and naturally occurring sugars. Processed carbs and refined sugars should be limited or avoided. How many carbs should endurance athletes eat? There will be some differences based on the type and duration of training.
This helps support the high volume of glucose needed for that level of physical activity. Each carb has 4 calories per gram. Endurance athletes should eat 8 to 10 grams of carbohydrate per kilogram kg of body weight per day.
This will depend on the duration of their endurance event. For endurance training lasting 4 to 5 hours, endurance athletes should consume 10 grams per kilogram of body weight. For example, an endurance runner who weighs 70 kg and competes in an endurance event lasting 4 hours or more should consume a minimum of grams of carbohydrate daily.
In comparison, a power athlete would consume fewer carbs around 4 to 5 grams per kilogram of body weight. A power athlete's focus would be more so to increase protein intake. Many people focus only on carbs for endurance exercise.
However, protein intake for endurance athletes is equally important. The purpose of protein is to build and replenish lean muscle tissue. Protein also acts as a source of energy in times of caloric deficits.
Animal-based protein, as the name implies, is protein that comes from animals. This type of protein is considered a complete protein. It is complete because it contains all nine essential amino acids.
Animal-based protein sources include:. Plant-based protein is protein that comes from plants. Plant-based protein is considered an incomplete protein. This isn't to say it is bad, it just doesn't have all essential amino acids.
Plant-based protein sources include:. Protein has 4 calories per gram. How much protein do you need to eat? Protein intake for a normal healthy adult is around 0. Endurance athletes should eat protein at 1. Athletes taking part in longer endurance events need more protein than those running shorter distances.
For example, endurance athletes weighing 70 kg would need to consume 98 grams of protein daily to support their endurance exercise. Athletes who take part in strength or power sports will consume up to 2. Endurance athletes on a plant-based diet will have an increased protein requirement.
Having a basic cadbohydrate of stress reduction exercises carbs are used during carbohydratw can take your training and performance to the next level, eventz carbohydrate endurancw is a piece Hormonal regulation Timing of carbohydrate intake for endurance events puzzle. By Long-term athletic success Johnson Last updated: December 20th, 6 min read. Having a basic understanding of how carbohydrates are used during exercise can take your training and performance to the next level, and carb loading is a piece of the puzzle. Back in high school, my water polo team hosted spaghetti nights, where the team would load up on carbohydrates the night before a big game. Carbohydrates are found in grains e. 
0 thoughts on “Timing of carbohydrate intake for endurance events”