The muscle mechanoreflex has been considered to make a small contribution to the cardiovascular response to exercise in healthy humans because no pressor response has been observed during stimulation of mechanosensitive receptors, such as static passive stretching, during many human studies. There is room for rethinking this consideration since the pressor response to upper limb exercise is greater than that to lower limb exercise. We examined whether static passive stretching of the forearm muscles causes a muscle mechanoreflex-induced pressor response in humans. Eighteen healthy men were recruited for this study. After a 15-min rest period in the supine position with a neutral (0°) wrist joint angle, all participants completed static passive stretching of the forearm for 60 s at four different intensities: minimal painful passive stretching (PPS), moderate-intensity passive stretching (MPS), low-intensity passive stretching (LPS), and no load (NL). During the procedure, beat-to-beat arterial blood pressure was measured using finger photoplethysmography. The force generated between the passively stretched hand and the experimenter's hands was recorded using a force transducer. Mean arterial pressure (MAP) during PPS and MPS significantly increased from baseline during the last 40 s (P < 0.05). MAP was significantly greater at 50 s and 60 s, depending on the intensity. MPS induced a greater peak response in MAP than lower intensities (P < 0.05). None of the subjects reported pain during the MPS and LPS trials. Static passive stimulation of the forearm is an effective method of isolating the muscle mechanoareflex-induced pressor response in humans.NEW & NOTEWORTHY The muscle mechanoreflex was considered to have a small contribution to cardiovascular regulation during exercise in healthy humans. In contrast, the results of this study indicate that static stretching of the forearm induces a pressor response in healthy humans and suggest that the mechanoreflex explicitly induces the pressor response during exercise in humans. The methods applied are useful for evaluating the pressor response to the mechanoreflex regardless of health, aging, and disease.
Keywords: arterial blood pressure; forearm; human subjects; muscle mechanoreflex.