Modulation of spontaneous baroreflex control of heart rate and indexes of vagal tone by passive calf muscle stretch during graded metaboreflex activation in humans

Abstract

We examined whether spontaneous baroreflex modulation of heart rate and other indexes of cardiac vagal tone could be altered by passive stretch of the human calf muscle during graded concurrent activation of the muscle metaboreflex. Ten healthy subjects performed four trials: a control trial, resting for 1.5 min (0% trial); or 1.5 min of one-legged isometric plantar flexor exercise at 30, 50, and 70% maximal voluntary contraction. The incremental increases in blood pressure (BP) caused were then partially sustained by subsequent local circulatory occlusion (CO). After 3.5 min of CO alone, sustained calf stretch and CO were applied for 3 min. Spontaneous baroreflex sensitivity (SBRS) was progressively decreased with increasing exercise intensity (P < 0.05). During CO, stretch decreased SBRS and increased BP similarly in all trials (P < 0.05). Within 15 s of stretch onset, heart rate (HR) increased by 6 +/- 1, 6 +/- 1, 8 +/- 1, and 6 +/- 2 beats/min in the 0, 30, 50, and 70% trials, respectively (P < 0.05), and root mean square of successive differences was decreased from CO-alone levels (P < 0.05). During the second and third minutes of stretch, HR fell back but remained significantly above CO levels, and common coefficient of variance of R-R interval decreased progressively with increasing prior exercise intensity (P < 0.05; 70% trial). This suggests that passive stretch of the human calf muscles decreases cardiac vagal outflow irrespective of the levels of BP increase caused by muscle metaboreflex activation and implies that central modulation of baroreceptor input, mediated by the actions of stretch-activated mechanoreceptive muscle afferent fibers, continues.

Acute Changes in Autonomic Nerve Activity during Passive Static Stretching

“…Since analysis was conducted for one minute in this study, not only cardiac sympathetic nerve activity that increases only at the start of SS, but also stimulation of the suppression system that subsequently occurs might be analyzed, and as a result, the balance of autonomic nerve activity is considered to shift to a parasympathetic nerve-dominant state. In addition,transient increases in SBP,DBP and HR have been reported in response to local SS of the triceps surae muscle [20,21,22], and our results support these previously described findings. Although the SS method was different in the previous studies, the transient changes in hemodynamic properties can be associated with mechanical stress and modulations of the baroreflex sensitivity and vagal tone during SS [20,21,22].…”

“…In addition,transient increases in SBP,DBP and HR have been reported in response to local SS of the triceps surae muscle [20,21,22], and our results support these previously described findings. Although the SS method was different in the previous studies, the transient changes in hemodynamic properties can be associated with mechanical stress and modulations of the baroreflex sensitivity and vagal tone during SS [20,21,22]. It is difficult to identify the mechanism from the results of this study; however, it is considered that the reduction in HR due to SS is mainly due to suppression of sympathetic nerve activity [2], and the reduction in HR plays a role in continuation of a parasympathetic nerve-dominant state by SS.…”

Blood pressure responses after a session of functional training in young adults and the elderly: a pilot study

“…Muscle fibres recruited activate mechanoreceptors, which elicit cardiovascular adjustments through parasympathetic withdrawal and sympathetic activation [10][11][12]. Furthermore, small muscle HUMAN MOVEMENT R.R.C.…”

Tai-chi-chuan and yoga onpostexercise hypotension: comparison to aerobic and resistance exercise

“…A session with static contraction associated to lexibility training during a session can affect hemodynamic responses (11). It is known that muscle ibers recruited activate mechanoreceptors, which elicit cardiovascular adjustments through parasympathetic withdrawal and sympathetic activation (12). Furthermore, small receptors of muscle iber also react to stretching in humans (13) with a signi icant impact on the initial heart rate(HR) acceleration.…”