Exercise‐induced sensitisation of stretch‐activated muscle mechanoreceptors? Effects on baroreflex sensitivity in man

Abstract

Baroreflex (BR) control of blood pressure (BP) and heart rate (HR) is regulated by central command and muscle afferent feedback. The influence of muscle mechanoreflex stimulation on the BR and its possible sensitisation during various levels of concurrent metaboreflex activation was assessed. 10 subjects performed 1.5mins of one-legged isometric plantarflexor exercise at 0, 30, 50 and 70% maximal voluntary contraction to produce incremental increases in BP during post-exercise circulatory occlusion (PECO). 3.5mins of PECO was followed by 3mins of passive calf stretch. Mean (±SEM) arterial pressures at rest were 86 ± 2, 89 ± 3, 93 ± 3 and 94 ± 3 mmHg prior to the 0, 30, 50 and 70% trials, respectively, and during PECO were 88 ± 3, 97 ± 3, 105 ± 3 and 111 ± 3 mmHg, respectively. Regression equations produced by sequence analysis of R-R intervals and systolic BP gave the mean slope values, representing spontaneous BR sensitivity (BRS), shown in the table below. Stretch significantly decreased BRS from both Rest and PECO, irrespective of exercise trial. The decrease in BRS during stretch, in the face of progressive elevations in BP during PECO and hence increased BR activation, might be explained by metabolite sensitisation of stretch-activated muscle mechanoreceptive afferents.