EFFECT OF GLYCOGEN DEPLETION ON HIGH INTENSITY EXERCISE PERFORMANCE

Abstract

PURPOSE Muscle glycogen depletion (GD) contributes to impaired exercise performance. However, since muscle glycogen hydrolysis can contribute to both aerobic and anaerobic ATP production, it is not clear how GD acts to reduce performance. The purpose of this study was to evaluate the pattern of aerobic and anaerobic energy use during high intensity cycling in relation to GD. METHODS Well trained cyclists (n=9), habituated to the task, performed randomly ordered 1500m cycle time trials in both normal (N) and GD states. Aerobic and anaerobic energy production were calculated from crank power output (SRM) and VO2. RESULTS Performance was significantly (p < 0.05) worse with GD (137.73 vs 133.96 s). In N vs GD, mean power output (323 vs 296 Watts), velocity (11.32 vs 11.09 m*s-1), aerobic energy production (22.7 vs 21.9 kJ) and anaerobic energy production (20.2 vs 18.7 kJ) were all significantly (p < 0.05) reduced by GD. The temporal evolution of power production revealed significant GD related losses in both aerobic (118 vs 105 Watts) and anaerobic (294 vs 273 Watts) power output during the first 300m of the trial. After this, there was a trend (p < 0.10) toward reductions in both aerobic (185 vs 177 Watts) and anaerobic (114 vs 102 Watts) power output with GD. CONCLUSIONS GD contributes to reductions in performance by compromising both aerobic and anaerobic power output.