A signalling role for muscle glycogen in the regulation of pace during prolonged exercise

Abstract

Introduction: In this study we examined the pacing strategy and the end muscle glycogen contents in eight cyclists, once when they were carbohydrate loaded and once when they were non-loaded. Methods: Cyclists completed 2 hours of cycling at ,73% of maximum oxygen consumption, which included five sprints at 100% of peak sustained power output every 20 minutes, followed immediately by a 1 hour time trial. Muscle biopsies were performed before and immediately after exercise, while blood samples were taken during the 2 hour steady state rides and immediately after exercise. Results: Carbohydrate loading improved mean power output during the 1 hour time trial (mean (SEM) 219 (17) v 233 (15) W; p,0.05) and enabled subjects to use significantly more muscle glycogen than during the trial following their normal diet. Significantly, the subjects, kept blind to all feedback except for time, started both time trials at similar workloads (,30 W), but after 1 minute of cycling, the workload average 14 W higher throughout the loaded compared with the non-loaded time trial. There were no differences in subjects' plasma glucose and lactate concentrations and heart rates in the carbohydrate loaded versus the non-loaded trial. Of the eight subjects, seven improved their time trial performance after carbohydrate loading. Finishing muscle glycogen concentrations in these seven subjects were remarkably similar in both trials (18 (3) v 20 (3) mmol/kg w/w), despite significantly different starting values and time trial performances (36.55 (1.47) v 38.14 (1.27) km/h; p,0.05). The intra-subject coefficient of variation (CV) for end glycogen content in these seven subjects was 10%, compared with an inter-subject CV of 43%. Conclusions: As seven subjects completed the time trials with the same end exercise muscle glycogen concentrations, diet induced changes in pacing strategies during the time trials in these subjects may have resulted from integrated feedback from the periphery, perhaps from glycogen content in exercising muscles.

Estratégia adotada em provas de natação estilo crawl: uma análise das distâncias de 800 e 1500m.

“…Alguns estudos têm sugerido que a diminuição gradual na produção de potência antes do sprint final impede a depleção prematura dos substratos energéticos e garante que estes recursos não estejam totalmente esgotados antes do término da prova 28,29 . Por exemplo, quando Rauch et al 29 submeteram ciclistas a duas condições, sendo uma dieta normal e outra carregada em carboidrato, foi notado que apesar dos sujeitos começarem ambas as provas em uma taxa de trabalho aproximada e terminarem com a mesma quantidade de glicogênio independente da dieta, um minuto após o início do teste, a potência externa na prova com a dieta carregada em carboidrato foi em média 14 W maior quando comparada a dieta normal. Isto sugere que a modificação na EP realizada na condição de dieta normal foi feita com o objetivo de conseguir manter a magnitude do sprint final, já que a EP parece ser determinada pela concentração inicial de glicogênio muscular 29 .…”

“…Por exemplo, quando Rauch et al 29 submeteram ciclistas a duas condições, sendo uma dieta normal e outra carregada em carboidrato, foi notado que apesar dos sujeitos começarem ambas as provas em uma taxa de trabalho aproximada e terminarem com a mesma quantidade de glicogênio independente da dieta, um minuto após o início do teste, a potência externa na prova com a dieta carregada em carboidrato foi em média 14 W maior quando comparada a dieta normal. Isto sugere que a modificação na EP realizada na condição de dieta normal foi feita com o objetivo de conseguir manter a magnitude do sprint final, já que a EP parece ser determinada pela concentração inicial de glicogênio muscular 29 . Além deste mecanismo fisiológico, sugere-se que este aumento na intensidade do exercício na parte final da prova pode ser explicado através do modelo de teleantecipação 30 .…”

Physiological and Psychological Effects of Deception on Pacing Strategy and Performance: A Review

“…Pacing strategy is said to be influenced by feedback information from both internal and external cues [6] . Oxygen saturation, glycogen levels [7] and metabolic fuel reserves, for example, act not just as metabolic by-products, but as internal signallers [1] . On the other hand, environmental conditions such as gradient, terrain, weather, oxygen content of inspired air, knowledge of the event (for example distance or duration] [8] , previous experience [9,10] and competition [11,12] all equate to external cues [13][14][15] .…”

Relationship between motor corticospinal excitability and ventilatory response during intense exercise

“…Therefore, it is likely that the decrease in MEP 16 16 would have been due to a reduction of the net excitability that occurred in the pathway from the motor cortex to the muscle. Since metabolic acidosis was attenuated in IE 2nd compared with that in IE 1st , low muscle glycogen concentrations rather than muscle acidosis might have exerted inhibitory effects on supraspinal areas of the central nervous system (Rauch et al 2005), causing the difference in MEP between the two IE trials.…”