Overall, research suggests that intramuscular glycogen is an important fuel supporting weight training exercise, but not the only substrate. Subjects 5 young men and one woman performed resistance exercise under a control CON condition no strenuous exercise for at least 48 hours prior to testing and after a carbohydrate restricted program EXP.

The EXP condition included 60 min of submaximal cycling and four 1 minute bouts of maximal exercise, followed by 48 hours of reduced carbohydrate intake. In comparing the CON to the EXP testing condition, the most observable difference was noted in squat performance, with no significant differences in the knee extension trials.

However, there was no difference between the CON and the EXP groups at any of the five contractile speeds of isokinetic knee extensions. In explaining the differing outcomes of the squat sets versus the knee extensions sets to an aerobic and carbohydrate restricted program , the authors summarized previous research that has depicted substrate utilization differences in the type of exercise.

Isometric exercise has been shown to be impaired by reducing glycogen content while no change has been seen in isokinetic exercise. The authors hypothesized the differences in the present study were also due to the type of exercise. The isokinetic exercise bouts consisted of relatively short duration 1.

It was felt the energy production of the isokinetic exercise was predominantly due to the breakdown of creatine phosphate while the utilization of glycogen was much more apparent in the longer lasting squat exercise regime.

The Effect of Carbohydrate Supplementation on Multiple Sessions and Bouts of Resistance Exercise For athletes completing multiple high-intensity strength training sessions per day, maintenance of muscle glycogen stores is critical.

In a study by Haff et al. During the second training session, the number of sets and repetitions performed were markedly higher with the carbohydrate consumption, and subjects were able to exercise for 30 minutes longer.

The authors concluded that athletes engaging in multiple exercise sessions per day ranging from mild to high intensity will receive a performance advantage with carbohydrate ingestion via maintenance of intramuscular glycogen stores, due to greater glycogen resynthesis during recovery.

In addition, the carbohydrate supplementation not only increased workout performance, it markedly increased workout duration. Practical Application For the recreational athlete participating in weight training, consideration of muscle glycogen stores is most satisfactory maintained with a well-balanced and calorically-sufficient diet.

It is necessary for personal trainers to consider the exercise habits and goals of their weight training clients before prescribing carbohydrate supplementation to benefit exercise performance.

So as not to let clients get carried away, it is meaningful to remind them that an excess of carbohydrate intake, exceeding bodily energy expenditure needs, will result in weight gain. References Essen-Gustavsson, B.

Glycogen and triglyceride utilization in relation to muscle metabolic characteristics in men performing heavy-resistance exercise. European Journal of Applied Physiology, 61, Haff, G. Robergs, R. Muscle glycogenolysis during differing intensities of weight-resistance exercise.

Journal of Applied Physiology, 70, Despite its importance, it is generally the case in humans and all animal species investigated so far that very little glycogen is stored in skeletal muscle and liver Fournier et al. In fact, we store just enough glycogen to sustain our energy demands for only a few hours of intense aerobic exercise Gollnick et al.

As a result, active individuals are at increased risks of experiencing a fall in their ability to engage not only in intense aerobic exercise Ivy, , but also in short sprint effort under situations eliciting fight or flight responses Balsom et al.

One obvious way to prevent the sustained depletion of muscle glycogen stores after exercise is to ingest carbohydrate-rich food to replenish rapidly these stores. It is not surprising, therefore, that there has been a large volume of research aimed at developing dietary strategies to optimise glycogen synthesis before and after exercise Ivy, ; Robergs, ; Burke et al.

What has not received the same level of attention, however, is how muscles replenish their glycogen stores when exposed to conditions expected to be highly unfavourable to glycogen synthesis. It is our objective here to review some of the most recent developments in this area.

One extreme dietary condition that would be expected to impair the synthesis of muscle glycogen during recovery from exercise is the absence of food. Is it possible for our muscles to re-build at least part of their glycogen stores after exercise if food is not available?

This is a situation likely to have had a major impact on the survival of our ancestors who, as a result of their hunter- gatherers life-style, were at increased risks of experiencing regular episodes of prolonged fast.

This notion that skeletal muscles might have the capacity to replenish their glycogen independently of food intake is not a novel one as it was central to the work of the Nobel Laureat, Otto Meyerhof, who, nearly a hundred years ago, provided evidence, based on the use of isolated frog muscle preparations, that skeletal muscles have such a capacity Fournier et al.

It is only over the past 30 years, however, that experiments have been performed in humans and a wide range of animal species to establish if this is also the case in intact animals.

The general consensus is that, after exercise, skeletal muscles in humans have the capacity to replenish at least part of their glycogen stores without food intake, irrespective of whether they are recovering from prolonged aerobic exercise Hultman and Bergström, ; Maehlum et al.

Moreover, we have also shown that this resynthesis occurs across all muscle fiber types Fairchild et al. This capacity to replenish muscle glycogen stores without food intake is not unique to our species, since it is now well established from our work and that of others that fish, amphibians, reptiles and other mammals have also the capacity to replenish their glycogen under these conditions reviewed in Gleeson, ; Milligan, , Palmer and Fournier, ; Fournier et al.

It is important to note, however, that until recently, there was some evidence that the rat was the only exception to this generalisation.

Although, during recovery from prolonged exercise of moderate intensity, rats have been shown to possess the capacity to replenish a large proportion of their stores of muscle glycogen without food intake Fell et al. These findings are somewhat problematic because they suggest that the rat cannot be adopted as an animal model for the study of this process.

For this reason, we have re- examined the suitability of the rat as an experimental model Nikolovski et al. Similarly, there is also resynthesis of muscle glycogen stores during recovery from a short sprint in the Western Chestnut mouse Bräu et al.

The observation that humans and other animal species can replenish at least part of their glycogen stores after exercise while fasting raises the question of the nature of the endogenous carbon sources recruited for this process. This depends to a large extent on the type of exercise from which one is recovering Fournier et al.

For instance, in response to prolonged exercise of moderate intensity resulting in only a marginal accumulation of lactate or glycolytic intermediates, these carbon sources play a role of marginal importance in the resynthesis of muscle glycogen in humans and rats, with most of the accumulated lactate being oxidised Brooks and Gaesser, ; Gaesser and Brooks, ; Favier et al.

There is strong evidence that, under these conditions, glycogen resynthesis occurs primarily at the expense of amino acids Favier et al. In response to a sprint, on the other hand, a large proportion of muscle glycogen stores is converted into lactate and, to a lesser extent, to glycolytic intermediates.

In humans and across all animal species studied to date, there is strong evidence that lactate, either directly or indirectly via its conversion to glucose, is a major carbon source for glycogen repletion under these conditions reviewed in Fournier et al.

We and others have also shown that the glycolytic intermediates can also contribute to glycogen repletion in humans and rats, but to a much lower extent Astrand et al.

What about other carbon sources such as the amino acids derived from the pool of free amino acids or protein breakdown and the glycerol released from the hydrolysis of triglycerides?

Although there is evidence that late into recovery these carbon sources might play some role in the replenishment of muscle glycogen Fournier et al.

The finding that lactate can be a major carbon source for the replenishment of muscle glycogen stores raises an intriguing question.

What if recovery from high intensity exercise were to occur under even less favourable conditions, where an increased proportion of the accumulated lactate is oxidised?

This is normally what is observed if mild exercise is performed during recovery from a sprint, a protocol of recovery known as active recovery. More lactate is oxidised during active recovery, in part, because lactate is used as a fuel by skeletal muscles under these conditions Bangsbo et al.

Since, as a result, less lactate is expected to be available for glycogen synthesis, this extreme type of recovery protocol would be predicted to impair glycogen repletion in the muscles of fasted individuals.

This is an issue that has been examined in several studies Peters-Futre et al. Interestingly, contrary to predictions, two of these studies reported that active recovery has no effect on muscle glycogen levels Peters-Futre et al.

In one of these studies Bangsbo et al. Moreover, as pointed out by Bangsbo and colleagues , suboptimal lactate accumulation might have contributed to the observed lack of glycogen deposition during recovery. This was not a limitation shared by the only other study which reported that active recovery is without any effect on glycogen synthesis Peters-Futre et al.

However, the statistical power of this latter study might have been too low for the detection of significant differences in glycogen levels between recovery protocols, given that glycogen accumulation in response to passive recovery was reported to be In support of the view that active recovery inhibits glycogen resynthesis is the observation that glycogen repletion in individuals fed carbohydrate post-exercise is impaired during active recovery Bonen et al.

Moreover, a more recent study also supports indirectly the view that glycogen synthesis is inhibited during active recovery Choi et al. Unfortunately, the impact of active recovery per se on glycogen synthesis was not examined in this study because no muscle sampling was performed at the end of the active recovery period Choi et al.

Also, since all the muscle biopsies were obtained through the same incision site in this study, and that this has been shown to impair glycogen synthesis Costill et al. One major limitation shared by all of the above mentioned studies on the effect of active recovery on glycogen repletion is that their focus is on changes in total muscle glycogen levels as a whole rather than across the individual muscle fiber types.

This can be a problem because the pattern of change in average muscle glycogen level can differ markedly from those of individual muscle fibers. For this reason, we have examined recently the response of muscle glycogen to active and passive recovery in humans, and shown, in agreement with others, that glycogen synthesis is impaired in the quadriceps muscle during active recovery, with glycogen remaining at stable levels Fairchild et al.

However, a distinct pattern of change in glycogen levels occurs at the level of the individual muscle fibers Fairchild et al. In comparison to passive recovery, where glycogen levels increase across all muscle fiber types, active recovery has no inhibitory effect on glycogen synthesis in type II muscle fibers, but causes a net glycogen breakdown in Type I muscle fibers Fairchild et al.

The observation that the average glycogen levels in the quadriceps muscle remain stable during active recovery is explained on the basis that Type I and II muscle fibers are present in comparable proportions in this muscle and the extent of net glycogen synthesis in Type II fibers matches that of glycogen breakdown in type I fibers Fairchild et al.

These findings thus show quite clearly that the pattern of change in total muscle glycogen during active recovery informs us little about the patterns of glycogen response across the individual muscle fibers.

Moreover, the fall in muscle glycogen in Type I fibers is consistent with these fibers being preferentially recruited in response to exercise performed at intensities comparable to those adopted for active recovery Vøllestad and Blom, It is important to note that, in an earlier study, Nordheim and Vøllestad reported that Type I and II muscle fibers also respond differently to active recovery, but no control group subjected only to passive recovery was included in this study, which makes it difficult to estimate the degree to which active recovery affects glycogen metabolism in these fibers.

The absence of any effect of active recovery on the replenishment of glycogen stores in Type II muscle fibers is surprising given the unfavourable hormonal environment associated with this recovery mode.

Indeed, we have shown that active recovery is associated with lower plasma glucose and insulin levels together with higher catecholamines concentrations than during passive recovery Fairchild et al. These conditions associated with active recovery should be unfavourable to glycogen synthesis because the stimulation of glucose transport and glycogen synthesis in skeletal muscle is not as marked if the levels of plasma glucose and insulin are reduced, whereas high catecholamines inhibit insulin-stimulated glucose uptake Chiasson et al.

Finally, the glycogenic drive associated with low intramuscular glycogen stores Richter, might be of such a magnitude that it overrides the impact of the unfavourable environment associated with active recovery on glycogen synthesis.

More research work will be required to test these hypotheses. The ability of Type II muscle fibers to replenish their glycogen stores under conditions expected to be highly unfavourable, such as food absence or active recovery, suggests that the maintenance of adequate glycogen stores in these fibers is of paramount importance.

Given that Type II muscle fibers are recruited mainly during intense exercise Vøllestad and Blom, , and that the depletion of muscle glycogen stores can affect one’s capacity to engage in a maximal sprint effort Balsom et al. This capacity to replenish muscle glycogen stores might not be a major issue in our modern societies, but for hunter-gatherers this is likely to have been of key importance to their survival.

Given the evidence that lactate is likely to be the major carbon source mobilised for the synthesis of muscle glycogen during passive, and maybe, active recovery, this raises the question of the metabolic pathway responsible for its conversion into muscle glycogen.

In theory, the synthesis of muscle glycogen from lactate could occur via two metabolic pathways, muscle lactate glyconeogenesis and the Cori cycle. These pathways have already been the object of numerous reviews McDermott and Bonen, ; Pascoe and Gladden, ; Palmer and Fournier, ; Donovan and Pagliassotti, ; Fournier et al.

The former pathway involves only the participation of skeletal muscles, and it differs from hepatic gluconeogenesis in that there is no intra-mitochondrial step involved, and the most recent evidence point to the reversal of the reaction normally catalysed by pyruvate kinase as being responsible for the conversion of pyruvate into PEP Palmer and Fournier, ; Dobson et al.

The Cori cycle, on the other hand, differs in many respects from lactate glyconeogenesis in that more than one organ are involved. Indeed, following its release from skeletal muscle, lactate is removed by the liver or kidneys where it is converted via gluconeogenesis into glucose.

Once produced, glucose is released into the blood before being taken up and stored as glycogen in skeletal muscles. Although, there is a general agreement that the former pathway plays the major role in glycogen synthesis from lactate in fish, amphibians and reptiles reviewed in Gleeson, ; Fournier et al.

Earlier studies in humans and rats have identified muscle lactate glyconeogenesis as the primary route responsible for lactate conversion into muscle glycogen Hermansen and Vaage, ; Astrand et al. What is still unclear, is the relative contributions of both pathways to the recycling of lactate into muscle glycogen reviewed in Fournier et al.

It is noteworthy that under conditions expected to be highly unfavourable to glycogen synthesis following high intensity exercise, such as food absence or active recovery, the rates of muscle glycogen synthesis in humans and rats are among the highest reported in the literature Pascoe and Gladden, ; Nikolovski et al, ; Fairchild et al.

This raises the issue of the mechanisms responsible for such a marked activation of muscle glycogen synthesis in fasted individuals. Arguably, the activation of glycogen synthase is expected to play a major role, irrespective of the pathways responsible for the conversion of lactate or other carbon sources into muscle glycogen.

In support of this view, we have shown that, in response to an intense sprint effort, the pattern of changes in the fractional velocity of glycogen synthase in the rat suggests that this enzyme undergoes a dephosphorylation-mediated activation at the onset of recovery Bräu et al.

As recovery progresses, the phosphorylation state of this enzyme returns to basal levels, at which point no further glycogen is being deposited Bräu et al.

As discussed previously Bräu et al. For the marked increase in the net rate of glycogen synthesis to occur during recovery from intense exercise, one might argue that it is important not only to activate glycogen synthase, but also to inhibit glycogen phosphorylase.

In agreement with this view, the pattern of change in the activity ratios of glycogen phosphorylase at the onset of recovery from high intensity exercise suggests that this enzyme experiences a transient dephosphorylation–mediated inhibition of its activity Bräu et al.

This raises the question of the role of this transient dephosphorylation of glycogen phosphorylase. This is an important question, since under other physiological conditions, such as during the starved-to–fed transition, it is possible to observe a rapid synthesis of glycogen despite the absence of any change in the phosphorylation state of glycogen phosphorylase James et al.

Under these conditions, a large fraction of glycogen phosphorylase is in its active phosphorylated form, but this is probably not enough for net glycogenolysis to occur because the levels of its activators or substrate AMP, IMP, Pi must also be elevated to activate glycogen phosphorylase Chasiotis, Since the onset of recovery from a short sprint is characterised by the accumulation of high levels of Pi, AMP and IMP in the cytosol, the transient dephosphorylation of glycogen phosphorylase might be one mechanism that prevents these metabolites from increasing glycogenolysis and substrate cycling between glycogen and glucose 1-phosphate, which otherwise would probably occur in the presence of elevated levels of these metabolites Bräu et al.

Since as discussed above, the Cori cycle plays an important role in the replenishment of muscle glycogen stores during recovery from high intensity exercise, it is not surprising that glucose transport in skeletal muscles is also activated under these conditions Kawanaka et al.

Although, as discussed above, the elevated catecholamine levels at the start of recovery would be expected to inhibit glucose transport, several factors are likely to counter their effects and contribute to the activation of glucose transport, namely the contraction-stimulated translocation of GLUT4 to the plasma membrane, the hyperinsulinaemia associated with a maximal sprint effort Pascoe and Gladden, ; Fairchild et al.

The acute activation of glucose transport in skeletal muscles is also one of several mechanisms that might contribute indirectly to the activation of glycogen synthesis at the onset of recovery from high intensity exercise. Indeed, there is compelling evidence that glucose transport has the capacity to control, at least in part, the rates of glycogen synthesis in skeletal muscles by altering glucose 6- phosphate levels Bloch et al.

Elevated levels of glucose 6-phosphate have the capacity to cause a fall in the phosphorylation state of glycogen synthase and phosphorylase because the binding of glucose 6-phosphate to these enzymes enhances their susceptibility to net dephosphorylation Bräu et al.

It is important to stress, however, that this does not explain the patterns of change in the phosphorylation state of these enzymes throughout most of the recovery period, since the rates of glycogen synthesis and phosphorylation state of glycogen synthase and phosphorylase change markedly and well after glucose 6-phosphate levels return to pre-exercise levels Bräu et al.

Overall, although the patterns of response of glucose transport, glycogen synthase and phosphorylase following high intensity exercise might explain, at least in part, the high rates of muscle glycogen synthesis post-exercise in fasting individuals, it is not clear which component plays the most important role in controlling these high rates of glycogen synthesis.

In conclusion, during recovery from exercise, it is possible for skeletal muscles to replenish their glycogen stores under conditions expected to be highly unfavourable to glycogen synthesis such as fasting or active recovery.

The rates of muscle glycogen synthesis can be very high under these conditions, most probably because of the acute activation of glucose transport and glycogen synthase and inhibition of glycogen phosphorylase. This capacity of skeletal muscles to replenish their glycogen stores under extreme conditions is clearly advantageous as it allows muscles to maintain adequate levels of glycogen stores for fight or flight responses.

Citations in ScholarGoogle. Author Information School of Human Movement and Exercise Science, University of Western Australia, Crawley, WA, , Australia.

Paul A. Publish Date Received: Accepted: Published online : Fournier, Timothy J. Fairchild, Luis D. Ferreira, Lambert Bräu. Journal of Sports Science and Medicine 03 , - Abstract Text Author biography References. Post-exercise glycogen repletion in the absence of food intake One extreme dietary condition that would be expected to impair the synthesis of muscle glycogen during recovery from exercise is the absence of food.

Carbon sources for post-exercise glycogen repletion in the absence of food The observation that humans and other animal species can replenish at least part of their glycogen stores after exercise while fasting raises the question of the nature of the endogenous carbon sources recruited for this process.

Muscle glycogen repletion during active recovery from intense exercise The finding that lactate can be a major carbon source for the replenishment of muscle glycogen stores raises an intriguing question.

Metabolic pathways responsible for the conversion of lactate into muscle glycogen Given the evidence that lactate is likely to be the major carbon source mobilised for the synthesis of muscle glycogen during passive, and maybe, active recovery, this raises the question of the metabolic pathway responsible for its conversion into muscle glycogen.

Regulation of post-exercise glycogen repletion in the absence of food intake It is noteworthy that under conditions expected to be highly unfavourable to glycogen synthesis following high intensity exercise, such as food absence or active recovery, the rates of muscle glycogen synthesis in humans and rats are among the highest reported in the literature Pascoe and Gladden, ; Nikolovski et al, ; Fairchild et al.

Conclusions In conclusion, during recovery from exercise, it is possible for skeletal muscles to replenish their glycogen stores under conditions expected to be highly unfavourable to glycogen synthesis such as fasting or active recovery. Astrand P. Journal of Applied Physiology 61, Balsom P.

Acta Physiologica Scandinavica , Bandyopadhyay G. Journal of Biological Chemistry , Bangsbo J. Journal of Physiology London ,

These results have been backed up and confirmed by many related studies 4,11, It is clear that glycogen is important, and the amount of glycogen that you have is also important. A normal, healthy 70 kg male eating a high carbohydrate diet might have around g 2, calories of carbohydrate stored as glycogen in their muscles, plus another 90g in the liver 5,6,7.

Compare this to about 10g of carbohydrates in the bloodstream 5,6,7 , and you can quickly see why glycogen is vital as a source of carbohydrates during exercise. A high carbohydrate diet is key to maintaining and maximizing glycogen stores 5,6,7. This is pretty straightforward, in order to store carbohydrates, you need to first eat carbohydrates.

There are some slightly more complex strategies for maximizing your glycogen stores, such as carbo-loading or carbohydrate periodization, that involve altering your carbohydrate intake in specific ways, but a more simple strategy will be easier to follow.

The simplest strategy is to maintain a high carbohydrate diet that reflects the energy requirements of your training or racing. The blog posts, Are you Fueling Enough on the Bike? and 3 Strategies to Get Lean and Stay Lean have more specific dietary recommendations.

There also appears to be a two-hour optimal window immediately after the cessation of exercise for the administration of carbohydrates. Simple carbohydrates appear to be the preferred replacement during this replenishment period.

Administration of. There is also some evidence that even smaller loads 28 grams every 15 minutes may induce even greater repletion rates. Therefore, at least 20 hours are required to recover muscle glycogen stores, even when the diet is optimal.

So, athletes working out two times per day should complete one workout at a diminished workload to relieve the reliance on glycogen reserves. The principle of glycogen resynthesis and supercompensation has great practical implications, not only in athletics, but also within industry for workers who consistently undergo depletion of glycogen stores due to prolonged bouts of exertion, or extended lifting tasks which would be glycolytic in nature; due to the duration, and also the myofibrillar ischemia induced by static contractions.

Previous Next. Submitted by: Gregory Tardie, Ph. Share this:. Sports Academy T February 11th, Sports Coaching , Sports Exercise Science , Sports Studies and Sports Psychology Comments Off on Glycogen Replenishment After Exhaustive Exercise. Performance-wise, things might even out regardless of carbohydrate choice.

Using more or less fat as fuel during a workout is not associated with losing body fat or body weight. As for losing body fat over time, look no further than good old and boring calories in vs. calories out. Burning more or fewer carbs or fat during a particular workout is not a thing for weight control or losing fat.

Studies that suggest a performance benefit from eating carbohydrates before training look at endurance training. Also, the more carbs you eat, the better, at least up to a specific limit. Research shows that 2. Before a training session, current carb intake recommendations suggest that a meal providing 1—4 grams per kilogram of bodyweight 3—4 hours ahead of the workout could be a good idea for peak performance.

You rely less on muscle glycogen if you provide carbs during exercise. You have less liver glycogen than muscle glycogen, and if you have liver glycogen left, you maintain your blood sugar better, helping your muscles oxidize more carbohydrates for energy.

Together, these effects allow you to train longer and harder by having some carbs ready to use during your training sessions. If you want to use many carbohydrates from outside sources during a workout, you need to trick your intestines.

Early studies showed that you absorb about 1 gram of glucose or maltodextrin per minute from your small intestine, then you saturate the transporters that move sugars through plasma membranes.

If you exercise even longer, you might benefit from up to 90 grams per hour. Commercial energy gels and home-made sugary lemonade works, too, as do any combination of these. The important thing is how your stomach reacts to carbs during a training session. A hundred grams of raisins improve your performance just as much as an expensive commercial energy gel but might also force you to jump into a shrub to relieve yourself halfway through your workout.

Competition day is not the time to try something new. Handle that during not-so-important training sessions. When it counts, you want to use something you know your stomach tolerates without issues. As usual, the research on the subject is endurance training-oriented. A couple of studies show improved performance when it comes to strength training, too.

Feel free to give it the old college try. Carb intake during exercise improves your performance even when the training session is shorter than an hour, even though your muscle glycogen should not be a limiting factor. You might not need to store carbs as glycogen or even digest them to benefit exercise performance.

Rinsing your mouth with a carbohydrate-rich liquid for 10 seconds every five to ten minutes during a workout seems to affect the central nervous system and your performance positively, even if you spit instead of swallowing.

Most mouth rinse-studies use cycling as the exercise of choice. One meta-analysis found that carbohydrate mouth rinses improve cycling power, but that this does not translate into decreased time to complete a cycling time trial. How is this relevant to glycogen?

You see, carbohydrate mouth rinsing is more effective if you exercise during a fast or when you eat a carbohydrate-restricted diet. When your muscle glycogen levels are low. That might sound counter-intuitive, but it seems to force your muscles to adapt to the situation, leading to better results in the long run.

You improve your exercise capacity when your muscles adapt to the demands you put on them. Adaptations include things like enhanced fat oxidation, angiogenesis the process of creating new blood vessels from existing ones , and a larger mitochondrial mass. Almost all the ATP, the primary energy source for your cells, is manufactured inside your mitochondria: the larger your mitochondrial mass, the more effective your ATP production.

Signals from your working muscles control these effects. When your muscles contract, like during a training session, a cascade of signals activates or shuts down metabolic pathways, controlling gene expressions and protein turnover. Many decades of exercise physiology research, beginning in the early s, show us methods to provide exercising muscle with as much carbohydrate as possible, before, during, and after workouts.

A plentiful supply of carbs is key to optimal performance. At the same time, more recent research suggests that your training results might improve if you regularly train without that plentiful supply of carbs.

You rob your muscles of their preferred fuel and force them to adapt to lesser sources. You also get a more effective fatty acid turnover in your muscles and your entire body.

The glycogen content in your muscles and how much carbs you eat add to these effects. That kind of carbohydrate restriction can improve your performance and training capacity over time.

In other words, you train without a lot of carbs leading up to a competition or an important event, and then you make sure you load your muscles with glycogen and eat plenty of carbs when it counts.

That way, you combine the greater training adaptations from carbohydrate restriction with the benefits of carbohydrate loading, giving you the best possible performance when you want it and need it the most. If restricting carbohydrates means better results, no carbohydrates do not mean even better results.

That could have the opposite effects, leading to low energy availability, fatigue, and even loss of muscle mass and depressed immune functions. Training without enough carbohydrates might be something for elite athletes who need optimal results at all costs to consider.

However, the casual athlete likely finds that method of training less than fun. And fun is integral to regular exercise habits. It has been busy keeping your blood sugar stable while you were snoring.

You force your body to use more fat as fuel during your workouts, increase the activity of enzymes controlling muscle glucose uptake, improve fat oxidation, and optimize mitochondrial function, compared to always loading up on carbs before your training sessions.

Exercising before breakfast like this leads to similar training adaptations in the long run as more dedicated carbohydrate restriction. As usual, strength training research is less abundant, and that research tends to be ambiguous. There is no consensus yet.

You get the same anabolic effects and stimulate muscle protein synthesis just as well regardless. The anabolic response to a strength training session is mainly dependent on signaling mechanisms and metabolic pathways, just like endurance training. However, the two different types of exercise activate different pathways.

One of the most powerful ones for building muscle is the so-called mTOR-complex. Signaling pathways activated by low energy availability and depleted glycogen reserves inhibit mTOR.

Muscle protein synthesis is the essential part of the muscle protein balance for building muscle mass. Muscle protein breakdown also factors in. Research from Swedish scientists suggests more significant muscle breakdown if you train with depleted muscle glycogen. Insulin, in turn, reduces muscle breakdown and improves nutrient uptake in your muscles.

Cut down on carbs, and your insulin levels drop. In theory, that might mean that you break down more muscle mass and provide your tired muscles with fewer nutrients with your post-workout meal.

Keep in mind that these are theoretical effects. Protein also releases plenty of insulin. Also, a very moderate insulin release reduces muscle breakdown maximally, and a normal-sized protein intake is enough for that insulin release.

When you lift weights, you primarily use muscle glycogen to fuel your efforts. If the same goes for strength training is unclear, even though your muscles rely on their glycogen stores to lift weights. Several studies suggest that you can handle a higher training volume if you eat carbohydrates before hitting the weights.

However, that allows you to conduct some unscientific experiments on your own. The same applies if you notice the opposite, that you perform better in a carb-loaded state. Training with more or less depleted glycogen levels and generally low carbohydrate availability lead to more stress hormones.

Markers indicating immune function are also negatively affected. Even though always exercising with a low carbohydrate availability might depress your immune system, the milder version of carb restriction, training before breakfast, does not seem to have any negative effects in this regard. If you are a big person, carry around a lot of muscle mass, or are more fit than the ordinary person, your capacity to store glycogen increases.

Fat is good enough. At higher intensities, your muscles switch to using an increasing amount of glycogen. As your glycogen levels deplete, you fatigue and start performing worse. If you only have 24 hours to restore your muscle glycogen following a workout, you better hurry!

You have to cram down around 10 grams of carbohydrates per kilogram of bodyweight in that time to make it. Also, you have to eat at least as many calories as your burn during that day. Glycogen synthesis is more effective if you eat several smaller carbohydrate-rich meals after a workout rather than loading up on one or two hefty ones.

One gram of carbohydrate per kilogram of body weight and hour during the hours following a training session optimizes glycogen restoration. You speed up your glycogen synthesis if you eat protein along with your carbs. Caffeine and creatine also cooperate with the carbohydrates you eat or drink, speeding up the rate at which you store glycogen in your muscles.

Eating 1—4 grams of carbs per kilogram of bodyweight 3—4 hours before a training session likely improves your endurance performance. As for strength training, the jury is out.