Abstract

More recently t 1/2 VO2 on has been shown to be significantly slower (t 1/2 = 70 to 120 s) for untrained individuals especially in the supine posture. The purpose of the present study was to examine the role played by central, Q, and peripheral, MBF2 circulatory adjustment in setting t 1/2 VO2 on. Q, HR, Pa, VO2, and La for eight subjects were measured during rest and exercise at 1.0 for arms and legs and 1.8 and 2.3 l.min for arm and leg pedaling in the supine posture. Three subjects exercised in the erect and supine posture at the same two work loads. In another study three fit and three unfit subjects exercised at the same work loads with arms and legs in the supine posture while MBF, VO2, and HR were determined continuously at rest and exercise. The t 1/2 VO2 on ranged from 24 s to 84 s depending on exercise and fitness. The t 1/2 Q for the same conditions ranged from 6 to 15 s and in virtually every case was less than t 1/2 VO2 on. The ranges in HR and Pa followed Q. The adjustment of MBF was complete in 6 to 18 s for fit and 30 to 40 s for unfit subjects, e.g., before VO2 reached t 1/2. Based on these observations, Q and MBF do not play arole in setting VO2 kinetics. The limitation therefore must be distal to the capillary circulation. Verf.-Referat