Carbohydrate is the critical substrate for bouts of endurance exercise, especially at higher intensities 1-5. It has been well established that higher carbohydrate intakes are advantageous for these sports, although some data has been collected, most of the recommendations for carbohydrate consumption in athletes undergoing resistance based exercise have been extrapolated from the endurance exercise based literature. The International Society of Sports Nutrition recommends 5-10 g/kg per day in athletes participating in moderate to high volumes of training 6, whereas Slater & Phillips 7 recommend a bit lower amount of 3-5 g/kg per day for strength and power athletes and 4-7 g/kg per day for body builders, other publications and position stands are in line with these recommendations 8,9 or are even higher 10.

Yet, multiple studies have not shown a decrement in resistance based performance metrics when the carbohydrate content of the diet was lowered 11-15. It is worth noting that these studies were acute in nature, and thus the time frame for depleting glycogen was not long enough to see chronic adaptations, and given the biopsy nature of the measurement, these studies did not collect muscle glycogen concentrations. Thus, we know very little about the effect of repeated exercise bouts on muscle glycogen concentrations in the low carbohydrate environment and how this may or may not effect performance and health in the short and long-term.

Recent research has also found that adding carbohydrate to an adequate bolus of protein post workout does not to increase muscle protein synthesis or attenuate muscle protein breakdown beyond adequate protein supplementation alone 16-18. Thus, given that up to 80% of ATP production during resistance training is derived from glycolysis 19, the benefit of adding carbohydrates post workout would theoretically almost exclusively come from enhanced restoration of glycogen concentrations 20 which can be reduced by up to 40% after an acute bout of resistance training 21. Yet, in humans, glycogen has been shown to be resynthesized to some degree with no food intake in the two hours post-workout 21. To quote the extremely thorough 2013 meta-analysis by Aragon & Schoenfeld 22,

“Considering the totality of evidence, maintaining a high intramuscular glycogen content at the onset of training appears beneficial to desired resistance training outcomes…Despite a sound theoretical basis, the practical significance of expeditiously repleting glycogen stores remains dubious… for goals that are not specifically focused on the performance of multiple exercise bouts in the same day, the urgency of glycogen resynthesis is greatly diminished… In scenarios of higher volume and frequency of resistance training, incomplete resynthesis of pre-training glycogen levels would not be a concern aside from the far-fetched scenario where exhaustive training bouts of the same muscles occur after recovery intervals shorter than 24 hours. However, even in the event of complete glycogen depletion, replenishment to pre-training levels occurs well-within this timeframe, regardless of a significantly delayed post-exercise carbohydrate intake.”

Given the discrepancy in the research with the current carbohydrate recommendations for athletes participating in resistance based training protocols more research is needed. Furthermore, to our knowledge there is a complete paucity of data on lower carbohydrate intakes in athletes that are combining both mechanical and metabolic stress in different types of circuit based training protocols that seem to be growing exponentially in popularity. The overall carbohydrate content of the diet has been found to be directly proportional to the amount of muscle glycogen 2. Thus, in the low carbohydrate setting, chronic glycogen depletion would be the most likely mechanism to result in long-term performance reductions and given that chronic glycogen depletion has been posited as a contributing factor to overtraining syndrome23, the primary aim of the current acute exercise and feeding trial was to assess whether glycogen could be resynthesized in highly trained male athletes in the 48 hour period after an acute bout of high-volume, resistance-based circuit training when carbohydrates were held at an average of 2g/kg per day, well below the current recommended intake for resistance trained athletes undergoing high volume training.


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