Different responses of muscle sympathetic nerve activity to sustained and rhythmic handgrip exercises.

Muscle sympathetic nerve activity (MSA) was recorded by microneurographic technique from the human tibial nerve before and during voluntary sustained and rhythmic handgrip exercises. The MSA increased significantly during sustained contractions but not during rhythmic contractions, whereas no differences in resting activity before the two modes of handgrip were seen at rest. The results demonstrate that MSA responses to sustained and rhythmic exercises are distinctly different, showing less sympathetic outflow during rhythmic than during sustained contraction.