Carbohydrate loading in practice: high muscle glycogen concentration is not certain.

It is believed that muscle glycogen resynthesis can be stimulated by depleting the glycogen stores by heavy physical exercise and then eating a diet rich in carbohydrates. In this study, we compared muscle glycogen concentrations after two different depletion and loading procedures in six male runners. The depletion runs for the procedures were a half-marathon race and an easier fartlek. The mean muscle glycogen concentrations (+/- s.e.m.), analysed after the procedures, did not differ significantly between the race and the fartlek being 285 (+/- 25) mmol/kg d.w. (dry weight) versus 315 (+/- 32) mmol/kg d.w. (P greater than 0.05). Moreover, the subjects' glycogen concentrations were not clearly increased above the predepletion values following either procedure. The results show that higher glycogen levels do not necessarily occur after classical carbohydrate-loading procedures.