Exercise-induced hypoxemia and anaerobic capacity in Thoroughbred horses

Abstract

Thoroughbred racehorses have been selectively bred for racing for centuries. The excellent exercise capacity of Thoroughbreds is thought to depend largely on their extraordinarily high cardiopulmonary function. Their high aerobic capacity (VO_2max) might be amplified by the exercise-induced hypoxemia that they experience even during submaximal exercise. In humans and horses, accumulated O₂ deficit (AOD) has been the primary approach used to assess net anaerobic capacity during exercise. The exercise-induced hypoxemia Thoroughbreds experience allows an alternative approach to measuring net anaerobic energy utilization using plasma lactate accumulation rate (PLAR). Horses increase their aerobic capacity when breathing hyperoxic gas that eliminates exercise-induced hypoxemia, and PLAR decreases stoichiometrically. Relating the decrease in PLAR to the increase in VO_2max yields a quantitative index of how much net aerobic power a horse is utilizing. Comparison in horses of the net anaerobic power estimated by the two methods, AOD and PLAR, shows systematic bias and suggests PLAR may be more accurate.