Muscle oxygen kinetics at onset of intense dynamic exercise in humans

TY - JOUR

T1 - Muscle oxygen kinetics at onset of intense dynamic exercise in humans

AU - Bangsbo, J

AU - Krustrup, P

AU - González-Alonso, J

AU - Boushel, Robert Christopher

AU - Saltin, B

PY - 2000

Y1 - 2000

N2 - The present study examined the onset and the rate of rise of muscle oxidation during intense exercise in humans and whether oxygen availability limits muscle oxygen uptake in the initial phase of intense exercise. Six subjects performed 3 min of intense one-legged knee-extensor exercise [65.3 +/- 3.7 (means +/- SE) W]. The femoral arteriovenous blood mean transit time (MTT) and time from femoral artery to muscle microcirculation was determined to allow for an examination of the oxygen uptake at capillary level. MTT was 15.3 +/- 1.8 s immediately before exercise, 10.4 +/- 0.7 s after 6 s of exercise, and 4.7 +/- 0.5 s at the end of exercise. Arterial venous O(2) difference (a-v(diff) O(2)) of 18 +/- 5 ml/l before the exercise was unchanged after 2 s, but it increased (P <0.05) after 6 s of exercise to 43 +/- 10 ml/l and reached 146 +/- 4 ml/l at the end of exercise. Thigh oxygen uptake increased (P <0.05) from 32 +/- 8 to 102 +/- 28 ml/min after 6 s of exercise and to 789 +/- 88 ml/min at the end of exercise. The time to reach half-peak a-v(diff) O(2) and thigh oxygen uptake was 13 +/- 2 and 25 +/- 3 s, respectively. The difference between thigh oxygen delivery (blood flow x arterial oxygen content) and thigh oxygen uptake increased (P <0.05) after 6 s and returned to preexercise level after 14 s. The present data suggest that, at the onset of exercise, oxygen uptake of the exercising muscles increases after a delay of only a few seconds, and oxygen extraction peaks after approximately 50 s of exercise. The limited oxygen utilization in the initial phase of intense exercise is not caused by insufficient oxygen availability.

AB - The present study examined the onset and the rate of rise of muscle oxidation during intense exercise in humans and whether oxygen availability limits muscle oxygen uptake in the initial phase of intense exercise. Six subjects performed 3 min of intense one-legged knee-extensor exercise [65.3 +/- 3.7 (means +/- SE) W]. The femoral arteriovenous blood mean transit time (MTT) and time from femoral artery to muscle microcirculation was determined to allow for an examination of the oxygen uptake at capillary level. MTT was 15.3 +/- 1.8 s immediately before exercise, 10.4 +/- 0.7 s after 6 s of exercise, and 4.7 +/- 0.5 s at the end of exercise. Arterial venous O(2) difference (a-v(diff) O(2)) of 18 +/- 5 ml/l before the exercise was unchanged after 2 s, but it increased (P <0.05) after 6 s of exercise to 43 +/- 10 ml/l and reached 146 +/- 4 ml/l at the end of exercise. Thigh oxygen uptake increased (P <0.05) from 32 +/- 8 to 102 +/- 28 ml/min after 6 s of exercise and to 789 +/- 88 ml/min at the end of exercise. The time to reach half-peak a-v(diff) O(2) and thigh oxygen uptake was 13 +/- 2 and 25 +/- 3 s, respectively. The difference between thigh oxygen delivery (blood flow x arterial oxygen content) and thigh oxygen uptake increased (P <0.05) after 6 s and returned to preexercise level after 14 s. The present data suggest that, at the onset of exercise, oxygen uptake of the exercising muscles increases after a delay of only a few seconds, and oxygen extraction peaks after approximately 50 s of exercise. The limited oxygen utilization in the initial phase of intense exercise is not caused by insufficient oxygen availability.

KW - Adult

KW - Blood Flow Velocity

KW - Blood Gas Analysis

KW - Capillaries

KW - Femoral Artery

KW - Femoral Vein

KW - Humans

KW - Hydrogen-Ion Concentration

KW - Kinetics

KW - Male

KW - Muscle, Skeletal

KW - Oxygen

KW - Oxygen Consumption

KW - Physical Exertion

KW - Thigh

M3 - Journal article

C2 - 10956247

SN - 0363-6119

SP - R899-R906

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

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

IS - Vol. 279 (48), No. 3

ER -