Whats different about the cardiovascular requirements of endurance exercise?
Exercising muscles produce excessive heat during work that must be balanced with efficient body cooling. Increases in cardiac output are required not only for working muscle, but also to supply blood flow to the skin to allow for optimal sweating and heat dissipation. In the endurance horse, the thermoregulatory system is of utmost importance. Comparatively, much more cardiac output is required for thermoregulation with endurance work than with short distance racing. During endurance exercise, fluid loss from sweating can reduce circulating blood volume. The resulting competition for cardiac output between working muscles and skin can become critical. Because the central cardiovascular needs take precedence, skin blood flow is reduced to maintain circulating blood volume and heat stress often results. The maximal heart rate in the horse varies from just over 200 to around 240 beats per minute. During racing, Thoroughbreds typically achieve heart rates that are close to maximum, while e
