Oxygen uptake kinetics of constant-load work: upright vs. supine exercise

The purpose of this study was to compare oxygen uptake (VO2), O2 deficit, steady-state VO2, and recovery VO2 during the performance of a constant-load exercise in the supine and upright position. Ten male subjects (36-40 yr) performed one submaximal exercise test in the supine and one in the upright position consisting of 5 min rest, 5 min cycle ergometer exercise at 700 kg X min-1 and 10 min of recovery from exercise. The VO2 was measured continuously in all tests from 2-L aliquot air samples collected every 30 s. Steady-state VO2 was similar during supine and upright exercise. However, total VO2 during upright exercise was 0.30 L greater (p less than 0.05) than during supine exercise while O2 deficit and recovery VO2 in the upright position were 0.64 L and 0.22 L less (p less than 0.05) compared to the supine test. The larger O2 deficit during supine exercise resulted from a significantly greater VO2 halftime compared to that of the upright response. Despite the ability to eventually attain similar steady-state VO2, supine exercise results in a reduction of total VO2 capacity associated with an increase in the O2 deficit during submaximal constant-load exercise and manifested by elevated recovery VO2.