Postural effect on cardiac output, oxygen uptake and lactate during cycle exercise of varying intensity

Abstract

Owing to changes in cardiac output, blood volume distribution and the efficacy of the muscle pump, oxygen supply may differ during upright and supine cycle exercise. In the present study we measured, in parallel, circulatory (heart rate, stroke volume, blood pressure) and metabolic parameters (oxygen uptake, lactic acid concentration [la]) during incremental-exercise tests and at constant power levels ranging from mild to severe exercise. In supine position, cardiac output exceeded the upright values by 1.0-1.5 l.min-1 during rest, light ([la] < 2 mmol.l-1) and moderate ([la] = 2-4 mmol.l-1) exercise. At higher exercise intensities the cardiac output in an upright subject approached and eventually slightly exceeded the supine values. For both rest-exercise transitions and large-amplitude steps (delta W > or = 140 W) the cardiac output kinetics was significantly faster in upright cycling. The metabolic parameters (VO2 and [la]) showed no simple relationship to the circulatory data. In light to moderate exercise they were unaffected by body position. Only in severe exercise, when cardiac output differences became minimal, could significant influences be observed: with supine body posture, [la] started to rise earlier and maximal power (delta W = 23 W) and exercise duration (64 s) were significantly reduced. However, the maximal [la] value after exercise was identical in both positions. The present findings generally show advantages of upright cycling only for severe exercise. With lower workloads the less effective muscle pump in the supine position appears to be compensated for by the improved central circulatory conditions and local vasodilatation.

Phase I dynamics of cardiac output, systemic O2 delivery, and lung O2 uptake at exercise onset in men in acute normobaric hypoxia

“…This being the case, then 1) if indeed the reduction of the A 1 of f H in hypoxia is due to lesser vagal withdrawal, then the same should be the case for the reduction of the A 1 of Q ; and 2) the Q st changes during an exercise transient are independent of mechanisms related to vagal withdrawal. Concerning the latter, in supine posture, a condition in which central blood volume is increased (24,29,47), phase I of Q is not evident (25,29), although resting vagal activation is greater supine than upright (25,38). A higher central blood volume would reduce the amount of blood suddenly displaced from the periphery to the heart by muscle pump action, and thus the size of the immediate increase in venous return, thus preventing an efficient Frank-Starling mechanism.…”

Relationship between oxygen uptake and oxygen supply system during constant-load supine exercise

“…In fact, SV slightly increases from rest to light exercise intensity and then does not change even if exercise intensity is increased [15]. Since exercise was started from pre-exercise to moderate or heavy exercise in this study, SV should have been constant.…”

Cardiopulmonary Responses at Various Angles of Cycle Backrest Inclination.

“…position [2][3][4][5][6][7][8] . In general, the AT and peak VO2, which are determined from cardiopulmonary exercise testing, were lower in the supine position than in the upright position 5)8) .…”

“…Many researchers have reported comparisons of cardiopulmonary responses during upright and recumbent (supine) exercises [2][3][4][5][6][7][8] . Generally, it has been reported that work performance in incremental exercise is enhanced in the upright position as .…”