Effects of muscle perfusion pressure on fatigue and systemic arterial pressure in human subjects

The effects of changes in arterial perfusion across the physiological range on the fatigue of a working human hand muscle were studied in seven normal subjects. With the hand above heart level, subjects made repeated isometri c contractions of the adductor pollicis muscle at 50% of maximal voluntary contraction in a 6-s on, 4-s off cycle. To assess fatigue, a maximal isomet ric twitch was elicited in each "off" period by electrical stimulation of t he ulnar nerve. The experiment was repeated at least 2 days later with the hand at heart level. Five subjects showed faster fatigue with the arm eleva ted, and two subjects showed little difference in fatigue for the two condi tions. Central blood pressure rose in proportion to fatigue for the subject s overall and returned quickly to its initial level afterwards. We conclude that human muscle fatigue can be increased by physiological reductions in perfusion pressure. Central blood pressure increases as the muscle fatigues , a response that may partially offset declining muscle performance.