Exercise that induces substantial muscle glycogen depletion impairs subsequent anaerobic capacity.

This study examines the effect of strenuous exercise on the aerobic and anaerobic capacity of horses, with a focus on the impact of muscle glycogen depletion. The results suggest that while aerobic metabolism remains unaffected, anaerobic metabolism is impaired when muscle glycogen stores are significantly reduced due to intense physical activity.

Research Design and Methods

• The study involved six fit Standardbred horses and encompassed three trials carried out seven days apart.
• Key measurements taken during each trial were the maximal rate of oxygen consumption (VO2max), maximal accumulated oxygen deficit (MAOD), muscle glycogen concentration, and blood lactate concentration.
• Between the second and third trials, the horses performed strenuous exercise over three consecutive days. This exercise was designed to significantly deplete the muscles’ glycogen stores.

Results and Findings

• Following the intense exercise period, the horses experienced at least a 55% reduction in muscle glycogen concentration.
• Maximal oxygen consumption rates (VO2max) in Trials 2 and 3 remained consistent, indicating that aerobic capacity was not affected by the glycogen depletion.
• In contrast, the decrease in run time to fatigue, accumulated oxygen deficit, and blood lactate levels in Trial 3 compared to Trial 2 suggested an impairment of anaerobic capacity.

Conclusion and Implications

• The research results indicate that strenuous, repeated exercise that significantly reduces muscle glycogen levels can hamper anaerobic metabolism in horses.
• However, the same amount of exercise does not affect aerobic metabolism. This differentiation in response to glycogen depletion between aerobic and anaerobic metabolism is an important insight and has implications for training and performance contexts.