Cardiovascular and autonomic responses in young adults during and after mechanoreflex activation via passive forearm stretching: are there sex differences?

Despite evidence suggesting that passive muscle stretching may enhance vagal modulation following the maneuver, its cardiovascular effects, particularly on cardiac baroreflex sensitivity (cBRS), during and after stretching, and potential sex-related differences remain unclear. This study investigated whether activation of the muscle mechanoreflex through passive forearm stretching elicits sex-specific cardiovascular responses and modulates cardiac autonomic regulation during recovery. Twenty-four healthy young adults (13 males; age: 23 ± 4 yr) were enrolled. After 10 min of supine rest with the wrist in a neutral position, participants completed two experimental conditions in randomized order on separate days: control and five sets of 1-min passive forearm stretching (15-s rest). Cardiovascular variables were continuously recorded, including beat-to-beat heart rate (ECG), finger arterial pressure (photoplethysmography), and brachial blood pressure (automated-sphygmomanometer). cBRS was assessed using the sequence method, which identified spontaneous sequences of rising (up) and falling (down) systolic pressure, followed by corresponding changes in RR interval. Measurements were obtained at baseline, during, immediately after, and 15 and 30 min after intervention for both conditions. Passive stretching elicited a significant increase in mean blood pressure, with a sex-specific difference (males: D9 ± 7 mmHg; females: D4 ± 4 mmHg; P ¼ 0.015). Vagal modulation increased during recovery (D11 ± 16 ms; P ¼ 0.019). cBRS-up enhanced poststretch (D3 ± 1 ms·mmHg^-1; P < 0.05), whereas cBRS-down showed no significant changes. Passive forearm stretching elicits a significant pressor response, which is greater in males, and promotes increases in cardiac vagal activity and cBRS-up, with no sex differences observed during the recovery period.