Effect of muscle glycogen availability on maximal exercise performance

Abstract

This investigation determined the influence of pre-exercise muscle glycogen availability on performance during high intensity exercise. Nine trained male cyclists were studied during 75 s of all-out exercise on an air-braked cycle ergometer following muscle glycogen-lowering exercise and consumption of diets (energy content approximately 14 MJ) that were either high (HCHO(80% CHO) or low (LCHO-25% CHO) in carbohydrate content. The exercise-diet regimen was successful in producing differences in pre-exercise muscle glycogen contents [HCHO: 578(SEM 55) mmol x kg(-1) dry mass; LCHO: 364 (SEM 58) P < 0.05 mmol x kg(-1) dry mass]. Despite this difference in muscle glycogen availability, there were no between trial differences for peak power [HCHO 1185 (SEM 50)W, LCHO 1179 (SEM 48)W], mean power [HCHO 547 (SEM 5)W, LCHO 554 (SEM 8)W] and maximal accumulated oxygen deficit [HCHO 54.4 (SEM 2.3) ml x kg(-1), LCHO 54.6 (SEM 2.0) ml x kg(-1)]. Postexercise muscle lactate contents (HCHO 95.9 (SEM 4.6) mmol x kg(-1) dry mass, LCHO 82.7 (SEM 12.3) mmol x kg(-1) dry mass, n = 8] were no different between the two trials, nor were venous blood lactate concentrations immediately after and during recovery from exercise. These results would indicate that increased muscle glycogen availability has no direct effect on performance during all-out high intensity exercise.

Effects of carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise

“…This may explain why carbohydrate intake and a high-carbohydrate diet do not affect time to exhaustion and anaerobic contribution during supramaximal exercise 6,27,28 . In this context, the study data reinforce the abovementioned results, showing that, like higher muscle glycogen content, an exogenous carbohydrate source has no positive effect on performance and anaerobic contribution during supramaximal exercise 5 . Although performance and anaerobic contribution did not change significantly, peak blood lactate had a moderate effect size (0.57), possibly because of higher pyruvate dehydrogenase complex activity, as reported by Galloway et al 3 .…”

“…Bergström & Hultman 4 found that muscle glycogen is not completely depleted during high-intensity exercises, so it is not a limiting factor for exercise performance. Moreover, higher availability of muscle glycogen after a high-carbohydrate meal has no effect on performance during highintensity exercise 5,6 . A plausible explanation for better performance in high-intensity exercises after carbohydrate intake is higher neuromuscular activation, which may lead to higher recruitment of type IIx fibers 7 and concomitantly increase anaerobic glycolysis 8 .…”

Metabolismo do glicogênio muscular durante o exercício físico: mecanismos de regulação

“…39 , a 125% VO 2max , a supercompensação de glicogênio levou a um aumento de 56% na concentração muscular inicial desse composto, sem, no entanto, aumentar a tolerência ao esforço (~175 s), ou modificar o acúmulo de lactato e de pH sangüíneos. Resultados similares foram encontrados por Hargreaves et al 40 , que não identificaram nenhum efeito da supercompensação de glicogênio muscular sobre a potência de pico, potência média e máximo déficit acumulado de oxigênio em exercício de 75 segundos (75 all-out). Entretanto, em atividades com exigên-cia mista ou participação efetiva da capacidade lática (aeróbio-anaeróbio com duração entre 3 a 10 minutos, isto é, próximo ao VO 2max ), a depleção de glicogênio muscular pode interferir significativamente no desempenho.…”

Less Is More: The Physiological Basis for Tapering in Endurance, Strength, and Power Athletes

“…Logically, a reduction in training volume during taper with proper diet reverses this condition (Figure 2) [10,24]. Initial muscle glycogen levels do not seem to affect short-term high-intensity performance (i.e., a sprint) [31,32]. Indeed, the performance decrements from overtraining [33] and the performance benefits from taper [26] can occur independent of muscle glycogen levels during shorter duration activities.…”