Static (isometric) exercise. Retrospection and introspection

This symposium summarizes current knowledge and serves to illustrate the many questions which must be considered and answered before the mechanisms which govern the cardiovascular adjustments to static exercise are understood. These include: What is the degree of mechanical hindrance to blood flow in statically contracting muscles? What are the characteristics of the receptors in muscle which are activated as a consequence of muscle contraction, the mechanism(s) of their activation, and the afferent fibers and central connections? What is the distribution of these receptors in different muscles and fiber types? What are the metabolic changes in muscles that accompany their contraction, and the relation of these to fiber type? To what degree do the higher centers in the brain dictate or mediate the cardiovascular responses? What is the role of muscle mass and tension in determining the responses to static exercise? What hemodynamic changes cause the increase in arterial pressure? What mechanisms cause the increase in heart rate? How do the arterial baroreceptors and cardiopulmonary vagal afferents modulate the primary hemodynamic changes caused by the muscle reflex and the higher centers? Do the same mechanisms control the cardiovascular responses during static and dynamic exercise with only quantitative differences, or do qualitative differences exist? What are the consequences of disease or physical training on the mechanisms responsible for the cardiovascular adjustments? In this paper the authors have tried to emphasize points of agreement, differences of viewpoints, and areas of ignorance.