Cardiovascular dynamics at the onset of exercise

At the onset of exercise, the cardiovascular system adapts with a series of integrated responses to meet the metabolic demands of the exercising muscl es. The importance of rapid increases in cardiac output and local muscle bl ood flow has been established by showing that small decreases in O-2 supply at the onset of exercise cause delays in the increase in O-2 utilization. With the development of techniques that can be applied to instantaneous mea surement of the cardiovascular response, the mechanisms that regulate incre ased muscle perfusion have recently been investigated. In this introduction to the symposium, a model of the within muscle distribution of blood flow is considered as a function of the measured responses across an exercising skeletal muscle. This model demonstrates the necessity of considering the d istribution of blood flow to the working fibers very early in exercise. The symposium provides insight into our current understanding of the factors i nvolved in the regulation of skeletal muscle blood flow at the onset of exe rcise. Our ability to study the impact of cardiovascular disease on exercis e performance has improved with the development of selective pharmacologica l agents to block or stimulate specific components of the cardiovascular re sponse. These advances should provide the basis for future research.