Kinetics of oxygen uptake during supine and upright heavy exercise

Shunsaku Koga, Tomoyuki Shiojiri, Manabu Shibasaki, Narihiko Kondo, Yoshiyuki Fukuba, Thomas J. Barstow
1999 Journal of applied physiology  
of oxygen uptake during supine and upright heavy exercise. J. Appl. Physiol. 87(1): 253-260, 1999.-It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V O 2 ) kinetics would be altered by body posture during heavy exercise [i.e., above the lactate threshold (LT)]. Nine subjects performed transitions from unloaded cycling to work rates representing moderate (below the estimated LT) and heavy exercise (V O 2 equal to 50% of the difference between LT and peak V O 2
more » ... n LT and peak V O 2 ) under conditions of upright and supine positions. During moderate exercise, the steady-state increase in V O 2 was similar in the two positions, but V O 2 kinetics were slower in the supine position. During heavy exercise, the rate of adjustment of V O 2 to the 6-min value was also slower in the supine position but was characterized by a significant reduction in the amplitude of the fast component of V O 2 , without a significant slowing of the phase 2 time constant. However, the amplitude of the slow component was significantly increased, such that the end-exercise V O 2 was the same in the two positions. The changes in V O 2 kinetics for the supine vs. upright position were paralleled by a blunted response of heart rate at 2 min into exercise during supine compared with upright heavy exercise. Thus the supine position was associated with not only a greater amplitude of the slow component for V O 2 but also, concomitantly, with a reduced amplitude of the fast component; this latter effect may be due, at least in part, to an attenuated early rise in heart rate in the supine position. posture; gas exchange kinetics; oxygen transport; slow component of oxygen uptake PULMONARY OXYGEN UPTAKE (V O 2 ) has been reported to adjust more slowly at the onset of exercise in the supine position for both moderate- (8, 15, 18, 19, 22, 25, 34) and heavy-intensity exercise (8, 9, 23) . Despite greater cardiac output (15, 18, 23) , it appears that effective blood flow to the working leg muscles is less in the supine posture (11, 13, 25, 33) , presumably as a consequence of lower arterial pressure in the legs when the effect of gravity (hydrostatic gradient effect) is removed. These results imply that the slowing of V O 2 kinetics in the supine position may be the result of a blunted cardiovascular response to exercise.
doi:10.1152/jappl.1999.87.1.253 pmid:10409583 fatcat:4lkp343onrdwji6nzofzslyxtu