Muscle Tensing During Standing

Abstract

Background and Purpose —When standing up causes dizziness, tensing of the leg muscles may alleviate the symptoms. We tested the hypothesis that leg tensing improves orthostatic tolerance via enhanced cerebral perfusion and oxygenation. Methods —In 10 healthy young adults, the effects of leg tensing on transcranial Doppler–determined middle cerebral artery (MCA) mean blood velocity ( V _mean ) and the near-infrared spectroscopy–determined frontal oxygenation (O ₂ Hb) were assessed together with central circulatory variables and an arterial pressure low-frequency (LF) (0.07 to 0.15 Hz) domain evaluation of sympathetic activity. Results —Standing up reduced central venous pressure by (mean±SEM) 4.3±2.6 mm Hg, stroke volume by 49±7 mL, cardiac output by 1.9±0.4 L/min, and mean arterial pressure at MCA level by 9±4 mm Hg, whereas it increased heart rate by 30±4 beats per minute ( P V _mean declined from 67±4 to 56±3 cm/s, O ₂ Hb decreased by 7±2.8%, and LF spectral power increased ( P P V _mean increased to 63±3 cm/s and O ₂ Hb increased by 2.1±2.6%, whereas LF power declined ( P Conclusions —During standing, tensing of the leg muscles attenuates a reduction in cerebral perfusion and oxygenation as it stabilizes central circulatory variables and reduces sympathetic activity.