Role of muscular factors in cardiorespiratory responses to static exercise: contribution of reflex mechanisms.

We investigated the effects of muscle mass and contraction intensity on the cardiorespiratory responses to static exercise and on the contribution afforded by muscle metaboreflex and arterial baroreflex mechanisms. Ten subjects performed static handgrip at 30% maximal voluntary contraction (MVC) (SHG-30) and one-leg extension at 15% (SLE-15) and 30% (SLE-30) MVC, followed by postexercise circulatory occlusion (PECO). Mean arterial pressure (MAP) and heart rate (HR) responses were greater during SLE-30 than during SHG-30. The difference in MAP was maintained by PECO, and the part of the pressor response maintained by PECO was greater after SLE-30 than after SHG-30 (88.3 +/- 10.6 and 67.8 +/- 12.7%, respectively, P = 0. 02). There were no differences in MAP and HR responses between SHG-30 and SLE-15 trials. Baroreflex sensitivity was maintained during SHG-30 and SLE-15, whereas it was significantly reduced during SLE-30 and recovered back to the resting level during PECO. Minute ventilation and oxygen uptake increased more during SLE-30 than during both SHG-30 and SLE-15 trials. Minute ventilation remained significantly elevated above rest only during PECO following SLE-30. These data suggest that during static exercise the muscle mass and contraction intensity affect 1) the magnitude of the cardiorespiratory responses, 2) the contribution of muscle metaboreflex to the cardiorespiratory responses, and 3) the arterial baroreflex contribution to HR control.