EFFECTS OF GLYCOGEN DEPLETION ON HIGH-INTENSITY EXERCISE PERFORMANCE AND GLYCOGEN UTILIZATION RATES

The aim of this study was to examine the effects of a decreased muscle glycogen concentration on metabolic and physiological responses to hi gh intensity exercise. Six Thoroughbred geldings of age 5.8+/-0.5 year s (mean+/-SEM) and body weight of 487+/-12 kg (mean+/-SEM) were random ly allocated to two treatments or control in a 3x3 Latin square repeat ed design. The experiment involved horses completing one of two differ ent glycogen depletion runs, aimed at depleting mainly type I (Protoco l A) and type II (Protocol B), with a run to exhaustion (RE) at 115% V O(2)max 5 hours after the glycogen depletion run. For muscle glycogen concentration, there was a significant difference between the three tr eatments at the p<0.05 level, with the post hoc test revealing that th e difference was between the control and both protocols A and B. There was no significant difference in muscle glycogen concentrations betwe en protocols A and B. Total glycogen utilized during RE runs were 188/-23.2, 204+/-12.3 and 146+/-43.6 mmol.kg(-1) for protocols A, B and C ontrol respectively. Mean rates of glycogen usage were 1.9+/-0.34, 2.2 +/-0.25 and 1.7+/-0.28 mmol.kg(-1)s(-1) for protocols A, B and Control respectively. There were no significant differences between protocols A, B and control. Mean run times were 103+/-9.2, 101+/-14.6 and 97+/- 12.0 s for protocols A, B and Control respectively and there was no si gnificant difference between these values. We concluded that muscle gl ycogen concentration in the horse can be reduced by 22% without having a significant effect on physical work capacity during high intensity exercise.