Circulatory response to static muscle contractions in three different muscle groups

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Abstract
Summary. The circulatory responses to static contractions of three different muscle groups were compared. Contractions at 15 and 25–30 % MVC of forearm muscles (hand‐grips) were compared to quadriceps muscle contractions in eleven male subjects, and in 10 subjects the response to hand‐grip contractions and foot plantar flexion was studied.All contractions at 15% MVC induced slight but significant changes in heart rate (HR); intra‐arterial blood pressure (BP) changes were more marked. 25–30 % MVC intensities always elicited a greater HR ‐and BP response than 15 % intensity in the same muscle group.Stroke volume (measured during hand‐grips and quadriceps contractions) was unchanged at all exercise intensities; hence, HR was a reliable measure of changes in cardiac output (Q). The circulation became hyperkinetic during exercise, since the rise in oxygen uptake was very slight despite a moderate increase in Q.Quadriceps contractions always elicited a larger HR, BP and Q response at a given time than hand‐grip contractions and the HR and BP at foot plantar flexion was always least marked. HR at exhaustion followed the same pattern. It is suggested that differences in functional properties of muscles are partly responsible for the magnitude of the reflex cardiovascular response during static contractions, but muscle strength and size may also influence the results.

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