LAUSR

Introduction 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. Methods 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 60s 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. Results Mean arterial pressure (MAP) during PPS and MPS significantly increased from baseline during the last 40s (P < 0.05). MAP was significantly greater at 50s and 60s, 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. Conclusion Static passive stimulation of the forearm is an effective method of isolating the muscle mechanoareflex-induced pressor response in humans.