Journal of Applied Physiology

Aging does not affect the sympathoinhibitory effect of the cardiopulmonary baroreflex during low-intensity dynamic exercise in males; however, its impact on females remains unknown. The reduction in muscle sympathetic nerve activity burst frequency during low-intensity leg cycling was smaller in older females than in younger females, even with similar changes in estimated central venous pressure. In females, muscle pump-induced inhibition of sympathetic vasomotor outflow during leg cycling may be attenuated with advancing age.

A hypobaric normoxia (HN) condition was used to disentangle the effects of hypoxia and hypobaria. There was an additive effect of hypobaria and hypoxia. Cerebral and muscular tissue oxygenation were lower in hypobaric normoxia than in normobaric hypoxia during rest and exercise. The effects of hypobaria were negligible in normoxia.

Here, we developed a statistical shape model, a geometric model that can quantify muscle morphology, particularly the quadriceps femoris muscle, to determine the influence of three-dimensional muscle shape on its force-generating capacity in young adults. The results revealed that curvature of the rectus femoris and bulging of vastus medialis were determinants of isometric knee extension strength, coupled with their muscle volumes. This morphological functionality relies on the critical relationship between muscle shape and mechanical advantage.