Effects of Posture on Cardiorespiratory Responses during Mild Exercise

In order to determine the effect of exercise posture on the cardiovascular and respiratory systems during mild exercise, nine healthy young males participated in this study. Cycle exercise was performed at 50 W and 150 W in both sitting and supine postures. The relative work intensity was on average 25%VO2max for 50 W and 50%VO2max for 150 W. Cardiac output and stroke volume were larger in the supine than in the sitting posture. The lower arteriovenous oxygen difference in the supine posture indicated a relative ineffectiveness of oxygen supply by the blood flow in the exercising muscles. Blood pressure and total peripheral resistance posture were lower in the supine than in the sitting posture, despite lower perfusion pressure in the exercising muscles, suggesting the relief of sympathetic nervous activity by the loading of arterial and cardiopulmonary baroreceptors. Heart rate was higher in the supine posture, suggesting a contribution from the cardiac depressor reflex in mild exercise. We concluded that despite the absence of metaboreflex during mild exercise, the cardiorespiratory responses in the different postures were at least apparently similar to those during moderate and heavy exercises.