Thigh oxygen uptake at the onset of intense exercise is not affected by a reduction in oxygen delivery caused by hypoxia

TY - JOUR

T1 - Thigh oxygen uptake at the onset of intense exercise is not affected by a reduction in oxygen delivery caused by hypoxia

AU - Christensen, Peter Møller

AU - Nordsborg, Nikolai Baastrup

AU - Nybo, Lars

AU - Mortensen, Stefan Peter

AU - Sander, Mikael

AU - Secher, Niels H.

AU - Bangsbo, Jens

N1 - CURIS 2012 5200 120

PY - 2012/10/15

Y1 - 2012/10/15

N2 - In response to hypoxic breathing most studies report slower pulmonary oxygen uptake (VO2) kinetics at the onset of exercise, but it is not known if this relates to an actual slowing of the Vo2 in the active muscles. The aim of the present study was to evaluate whether thigh VO2 is slowed at the onset of intense exercise during acute exposure to hypoxia. Six healthy male subjects (25.8 ± 1.4 yr, 79.8 ± 4.0 kg, means ± SE) performed intense (100 ± 6 watts) two-legged knee-extensor exercise for 2 min in normoxia (NOR) and hypoxia [fractional inspired oxygen concentration (FiO2) = 0.13; HYP]. Thigh Vo2 was measured by frequent arterial and venous blood sampling and blood flow measurements. In arterial blood, oxygen content was reduced (P < 0.05) from 191 ± 5 ml O2/l in NOR to 180 ± 5 ml O2/l in HYP, and oxygen pressure was reduced (P < 0.001) from 111 ±4 mmHg in NOR to 63 ± 4 mmHg in HYP. Thigh blood flow was the same in NOR and HYP, and thigh oxygen delivery was consequently reduced (P < 0.05) in HYP, but femoral arterial-venous oxygen difference and thigh Vo2 were similar in NOR and HYP. In addition, muscle lactate release was the same in NOR and HYP, and muscle lactate accumulation during the first 25 s of exercise determined from muscle biopsy sampling was also similar (0.35 ± 0.07 and 0.36 ± 0.07 mmol·kg dry wt-1·s-1 in NOR and HYP). Thus the increase in thigh VO2 was not attenuated at the onset of intense knee-extensor exercise despite a reduction in oxygen delivery and pressure.

AB - In response to hypoxic breathing most studies report slower pulmonary oxygen uptake (VO2) kinetics at the onset of exercise, but it is not known if this relates to an actual slowing of the Vo2 in the active muscles. The aim of the present study was to evaluate whether thigh VO2 is slowed at the onset of intense exercise during acute exposure to hypoxia. Six healthy male subjects (25.8 ± 1.4 yr, 79.8 ± 4.0 kg, means ± SE) performed intense (100 ± 6 watts) two-legged knee-extensor exercise for 2 min in normoxia (NOR) and hypoxia [fractional inspired oxygen concentration (FiO2) = 0.13; HYP]. Thigh Vo2 was measured by frequent arterial and venous blood sampling and blood flow measurements. In arterial blood, oxygen content was reduced (P < 0.05) from 191 ± 5 ml O2/l in NOR to 180 ± 5 ml O2/l in HYP, and oxygen pressure was reduced (P < 0.001) from 111 ±4 mmHg in NOR to 63 ± 4 mmHg in HYP. Thigh blood flow was the same in NOR and HYP, and thigh oxygen delivery was consequently reduced (P < 0.05) in HYP, but femoral arterial-venous oxygen difference and thigh Vo2 were similar in NOR and HYP. In addition, muscle lactate release was the same in NOR and HYP, and muscle lactate accumulation during the first 25 s of exercise determined from muscle biopsy sampling was also similar (0.35 ± 0.07 and 0.36 ± 0.07 mmol·kg dry wt-1·s-1 in NOR and HYP). Thus the increase in thigh VO2 was not attenuated at the onset of intense knee-extensor exercise despite a reduction in oxygen delivery and pressure.

U2 - 10.1152/ajpregu.00201.2012

DO - 10.1152/ajpregu.00201.2012

M3 - Journal article

C2 - 22933023

SN - 0363-6119

VL - 303

SP - R843-R849

JO - American Journal of Physiology - Regulatory Integrative and Comparative Physiology

JF - American Journal of Physiology - Regulatory Integrative and Comparative Physiology

IS - 8

ER -