Ventilatory response at the onset of exercise in human

Abstract

When exercise starts, various cardiorespiratory adjustments take place for accommodating the greatly increased metabolic requirements. It is well known that the transition from rest to light or moderate intensity exercise is typically accompanied by an abrupt step-1ike increment in ventilation at the first exercise breath. This rapid increment of ventilation at the onset of exercise (phase I) is observed during not only voluntary and passive exercise, but also during electrically induced muscle contraction. A rapid response in ventilation (phase I) may be at least useful for preventing oxygen deficiency and for increasing alveolar ventilation, oxygen tension, and oxygen uptake even if it is a small quantity. Although mechanisms of phase I have extensively been explored by many investigators, they have still remained obscure until now. At present, the causal factors of phase I are classified as central (descending) and peripheral (ascending) neurogenic stimulus, or as both. In the awake condition, abrupt ventilatory increment immediately after voluntary and passive exercise in man could be attributed to the drives from the central command including cortical and hypothalamic activities as well as some peripheral afferent information mainly through group III and IV fibers. However, further investigation to clarify many unsolved problems regarding neurogenic mechanisms of phase I should be advanced in future.