V′O2 kinetics was investigated before and after 14 days of head-down tilt (-6°) bed rest (HDT) and of control ambulatory period (AMB) in 11 healthy males at two sub-maximal workloads testing the hypothesis that the altered cardiovascular response to exercise ensuing after bed rest could make it slower. Breath-by-breath oxygen uptake (V′O2) was measured during square-wave cycling exercise calculating it from respiratory gas fractions and ventilatory flow recorded at the mouth. Exercise was performed at two exercise intensities (W1, W2) ranging from: i) W1: 53.6 % of V′O2max ±8.3 % to 58.9±16.9 % and W2: 83.6±15.6 % to 84.7±13.3 % before and after HDT respectively, and; ii) W1: 55.2±9.7 % to 58.9±6.2 % and W2: 83.3±4.2 % to 84.2±7.7 %, before and after AMB. V′O2 data were fitted by means of a bi-exponential model. In HDT and AMB, V′O2max values decreased: from 3.0 1 min-1 ±0.41 to 2.6 ± 0.32 (HDT), and from: 3.0±0.55 to 2.8±0.21 (AMB). Phase II time constants of V′O2 kinetics (τ2) in HDT equalled to: i) 24.8 s ± 4.65 (W1 and 22.2 s±3.65 (W2) before bed rest and; ii) 26.5 s±5.00 and 24.3 s±4.26 after bed rest. In AMB, τ2 turned out to be: i) 25.2 s±4.35 (W1) and 23.9±4.34 (W2) before and; ii) 26.0 s±4.21 and 24.3 s±4.22 after AMB. These data indicate a significantly slower V′O2 kinetics after HDT (by 6.9 % and 9.5 % at W1 and W2, respectively). Oxygen pulse at the two relative workloads turned out to be by 13.9 % and 17.6 % lower after HDT, but it decreased only by 1.9 % and 6.1 % after AMB, thus suggesting a remarkable decrease of the stroke volume during sub-maximal exercise in HDT as compared with AMB.
Oxygen uptake at the onset of step-exercise before and after short duration bed rest in humans
Ferretti G.
2002-01-01
Abstract
V′O2 kinetics was investigated before and after 14 days of head-down tilt (-6°) bed rest (HDT) and of control ambulatory period (AMB) in 11 healthy males at two sub-maximal workloads testing the hypothesis that the altered cardiovascular response to exercise ensuing after bed rest could make it slower. Breath-by-breath oxygen uptake (V′O2) was measured during square-wave cycling exercise calculating it from respiratory gas fractions and ventilatory flow recorded at the mouth. Exercise was performed at two exercise intensities (W1, W2) ranging from: i) W1: 53.6 % of V′O2max ±8.3 % to 58.9±16.9 % and W2: 83.6±15.6 % to 84.7±13.3 % before and after HDT respectively, and; ii) W1: 55.2±9.7 % to 58.9±6.2 % and W2: 83.3±4.2 % to 84.2±7.7 %, before and after AMB. V′O2 data were fitted by means of a bi-exponential model. In HDT and AMB, V′O2max values decreased: from 3.0 1 min-1 ±0.41 to 2.6 ± 0.32 (HDT), and from: 3.0±0.55 to 2.8±0.21 (AMB). Phase II time constants of V′O2 kinetics (τ2) in HDT equalled to: i) 24.8 s ± 4.65 (W1 and 22.2 s±3.65 (W2) before bed rest and; ii) 26.5 s±5.00 and 24.3 s±4.26 after bed rest. In AMB, τ2 turned out to be: i) 25.2 s±4.35 (W1) and 23.9±4.34 (W2) before and; ii) 26.0 s±4.21 and 24.3 s±4.22 after AMB. These data indicate a significantly slower V′O2 kinetics after HDT (by 6.9 % and 9.5 % at W1 and W2, respectively). Oxygen pulse at the two relative workloads turned out to be by 13.9 % and 17.6 % lower after HDT, but it decreased only by 1.9 % and 6.1 % after AMB, thus suggesting a remarkable decrease of the stroke volume during sub-maximal exercise in HDT as compared with AMB.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
