DIFFERENTIAL-EFFECTS OF TRAINING ON THE CONTROL OF SKELETAL-MUSCLE PERFUSION

Endurance and high-intensity sprint training have been shown to alter skeletal muscle blood flow and factors that govern muscle perfusion un der various conditions. Neither endurance nor sprint training alter sk eletal muscle perfusion at rest but can result in an increase in muscl e blood flow during the anticipation of exercise. The magnitude of the anticipatory increases in muscle blood flow is dependent on the inten sity and duration of the prior training bouts and results from elevati ons in mean arterial pressure and decreases in vascular resistance in skeletal muscle. The decrements in skeletal muscle vascular resistance appear to be mediated through increases in muscle sympathetic choline rgic nerve activity or decreases in muscle sympathetic adrenergic nerv e activity. During submaximal exercise, total muscle blood flow is eit her unchanged or slightly lower. However, a redistribution of muscle b lood flow may occur following aerobic training: resulting in an enhanc ed perfusion of high-oxidative skeletal muscles and less flow going to low-oxidative muscles. The increased perfusion of the high-oxidative muscles may result from various factors including: a) increased recrui tment of high-oxidative motor units, b) increased local release of met abolic vasodilator substances, c) qualitative changes in the metabolic substances released, d) decreased muscle sympathetic nerve activity, e) diminished sensitivity of the arterial vasculature to norepinephrin e or other vasoconstrictor agents, f) enhanced endothelium-mediated di lation in the resistance vasculature, and g) an increased effectivenes s of the skeletal muscle pump. Conversely, the decreases in blood flow to low-oxidative muscles may result from an enhanced autoregulatory r esponsiveness of the resistance vasculature. Endurance and sprint trai ning increase muscle perfusion during exercise at (V)over dot O-2max; this primarily appears to be the result of an enhanced pumping capacit y of the heart to increase in maximal cardiac output. Many of the trai ning-induced alterations in muscle blood flow and vascular structure a re localized in the muscles that are most active during the training b outs. Therefore, differences in muscle recruitment patterns that occur with low-intensity endurance exercise and high-intensity sprint exerc ise may account for differences observed between these two training re gimens.