Increases in cardiac vagal modulation following a single session of passive calf stretching

Abstract

Autonomic cardiovascular responses to mechanoreflex activation by passive muscle stretching have been shown in numerous investigations. These cardiovascular adjustments include cardiac vagal inhibition, sympathetic activation, pressor response, and baroreflex resetting. However, it is currently unclear how the autonomic system responds after a single session of passive muscle stretching. Therefore, we aimed to test the hypothesis that there would be parasympathetic dominance after stretching cessation. Twenty-four volunteers (14 men; 22±3 yr) performed two protocols: 1) five sets of 1 minute of unilateral passive calf stretching with 15 s of rest; and 2) control condition (six minutes of resting at the same position). The autonomic cardiac responses of both control and experimental conditions were assessed before, and immediately, 15 minutes and 30 minutes after stretching cessation. Passive stretching was performed on an isokinetic dynamometer (Biodex System 4, USA). Heart rate, systolic and diastolic blood pressure were continuously measured on a beat-to-beat basis using lead II electrocardiography (BioAmp, MLA2540) and finger photoplethysmography (Human NIBP, Australia). Brachial arterial blood pressure was also measured with an automated digital sphygmomanometer (Dixtal, DX2022, Brazil). Heart rate variability (HRV) was determined following the guidelines of the Task Force of the European Society of Cardiology and the North American Society of Pacing. With regards to the hemodynamics variables, there was no significant difference in the heart rate before and after passive stretching, while mean blood pressure (MBP) was slightly higher (±2mmHg) 30 min following both protocols (control, p=0.027 and stretch, p=0.035). Regarding HRV analysis, in the time domain, RMSSD was significantly increased 30 min following passive stretching (+15%; p=0.029), and this effect was also detected when using the frequency domain (high frequency: +37%, p=0.039). Of note, our major findings were not affected by sex. In conclusion, autonomic cardiovascular control shifts to a parasympathetic dominant state following passive calf stretch, and the effect peaks around 30 minutes after stretching. Passive stretching seems to be a safe, easy, and effective form of exercise that evokes autonomic cardiovascular responses during and following its cessation, even if it is performed in a single session of stretch. CNPq 307764/2022-2; CAPES (001) QUT South America Scholarship. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.