1. 1. The aim of the present study is to assess the relationship between rapidity of oxygen uptake (VO2 and cardiac output (Q) kinetics at the transient phase of the onset and offset of exercise.
2. 2. Five healthy male subjects performed multiple rest-exercise-recovery transitions on an electrically braked ergometer, work rate was 50, 75, or 100 W for 6 min, respectively.
3. 3. VO2 was obtained by a breath-by-breath method, and Q was measured by an impedance method during normal breath, using an ensemble averaged method.
4. 4. On transition from rest to exercise, VO2 rapidly increased as phase I with a time constant of 7.0–7.8 s. Q also showed a similar rapid increment with a time constant of 6.3–6.8 s in phase I.
5. 5. In this phase I, VO2 increased approx. 42–68% of steady state value and Q increased 71–84%. Thereafter, VO2 and Q increased monoexponentially up to steady state with a time constant of 26.7–32.3 and 23.7–34.4 s, respectively.
6. 6. During recovery, VO2 (with a time constant of 35.7–38.1 s and time delay (TD) of −1 to −2 s), while Q remained to sustain the value of steady state exercise with a couple of time delay (TD = 2–7 s), and thereafter decreased monoexponentially (with a time constant of 18.9–31.6 s).
7. 7. The stroke volume showed the similar behavior to the Q kinetics after exercise, while heart rate rapidly decreased (time constant = 10.6–21.2 s).
8. 8. It is suggested that the delayed Q kinetics after exercise might be attributable to the sustained level of venous return and that Q kinetics is not linked with VO2 kinetics after exercise.
Author Keywords: VO2 kinetics; Q kinetics; exercise
