Muscle glycogen depletion and subsequent replenishment affect anaerobic capacity of horses

The purpose of this study was to determine the effect of muscle glycogen de pletion and subsequent replenishment on anaerobic capacity of horses. In a blinded crossover study, seven fit horses performed glycogen-depleting exer cise on two occasions. Horses were infused after glycogen-depleting exercis e with either 6 g/kg body wt of glucose as a 13.5% solution in 0.9% NaCl (G lu) or with 0.9% NaCl (Sal) of equivalent volume. Subsequently, horses perf ormed a high-speed exercise test (120% of maximal rate of oxygen consumptio n) to estimate maximum accumulated oxygen deficit. Replenishment of muscle glycogen was greater (P < 0.05) in Glu [from 24.7 +/- 7.2 (SE) to 116.5 +/- 7 mmol/kg wet wt before and after infusion, respectively] than in Sal (fro m 23.4 +/- 7.2 to 47.8 +/- 5.7 mmol/kg wet wt before and after infusion, re spectively). Run time to fatigue during the high-speed exercise test (97.3 +/- 8.2 and 70.8 +/- 8.3 s, P < 0.05), maximal accumulated oxygen deficit ( 105.7 +/- 9.3 and 82.4 +/- 10.3 ml O-2 equivalent/kg, P < 0.05), and blood lactate concentration at the end of the high-speed exercise test (11.1 +/- 1.4 and 9.2 +/- 3.7 mmol/l, P < 0.05) were greater for Glu than for Sal, re spectively. We concluded that decreased availability of skeletal muscle gly cogen stores diminishes anaerobic power generation and capacity for high-in tensity exercise in horses.