Transient O2 uptake response at the onset of exercise.

One purpose of this study was to determine whether the half time of the oxygen consumption (VO2) response at the onset of exercise varies with work intensity. Fifteen subjects performed 5 min of bicycle ergometer exercise across a range of relative work loads with VO2 determined continuously via computer analysis. The results revealed that the half time of the VO2 response increased as work intensity increased. Our second purpose was to determine whether VO2 response kinetics are dependent on the maximum oxygen uptake (VO2max) of the subject. When VO2 response kinetics were compared at equal absolute work loads for a highly trained (n = 8, mean VO2max = 70.2 ml/kg.min) and an untrained (n = 7, mean VO2max = 49.7 ml/kg.min) group, the highly trained group had a more rapid VO2 response (P less than 0.05). The same tendency was evident at equal relative work loads but the differences were not significant. The more rapid adaptation of the highly trained subjects at absolute work loads may be caused by the enzymatic and circulatory adaptations which result from endurance training. The more rapid adjustment of VO2 at the onset of exercise may explain the slower phosphagen and glycogen depletion found in highly trained subjects following short-term work at equal absolute loads.