Cardiopulmonary Mechanoreflexes

Some studies have demonstrated that an initial complex response of the heart rate, i.e., a sharp increase and a subsequent level off or slight decrease, at the onset of voluntary exercise, is induced by dynamic muscle contractions as standing, handgrip exercise, and leg exercise, but not induced by passive tilt standing. The initial fluctuation in heart rate during the early phase of physical activity has been reported to be attributable to the initial withdrawal of vagal efferent nerve activity and transient retrieval of vagal efferent nerve input in sequence. These studies have also demonstrated a complex response of the heart rate or an overshoot at the onset of upright exercise at almost only light to mild workloads; however, if a person exercises a heavy workload, the complex change in heart rate at the beginning hardly appears but rather increases exponentially. So far, little is known about the mechanisms whereby the heart rate is sustained below its initial peak or suppressed from a gradual increase. Such a fluctuation in heart rate is a very interesting phenomenon, highlighting the significance of circulatory function, because light physical activity is often inherent on a daily basis.