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O2 during repeated bouts of heavy knee extension exercise in humans
1 Department of Exercise Science and Physiology, School of Health Sciences, Hiroshima Prefectural Women's University, Hiroshima 734–8558, Japan2 Laboratory of Health and Exercise Science, Hiroshima Institute of Technology, Hiroshima 731–5193, Japan3 Laboratory of Physical Activity and Health Evaluation, National Institute of Health and Nutrition, Tokyo 162–8636, Japan4 Laboratory for Applied Physiology, Kobe Design University, Kobe 651–2196, Japan5 Laboratory for Human Science and Biomedical Engineering, National Institute of Advanced Industrial Science and Technology, Tsukuba 305–8563, Japan.
It has frequently been demonstrated that prior heavy cycling exercise facilitates pulmonary 
O2 kinetics at the onset of subsequent heavy exercise. This might be due to improved muscle perfusion via acidosis-induced vasodilating effects. However, it is difficult to measure the blood flow (BF) to the working muscles (via the femoral artery) during cycling exercise. We therefore selected supine knee extension (KE) exercise as an alternative, and investigated whether the faster O2 kinetics in the 2nd bout was matched by proportionally faster BF kinetics to the exercising muscle. Nine healthy subjects (aged 21–44 years) volunteered to participate in this study. The protocol consisted of two consecutive 6-min KE exercise bouts in a supine position (work rate: 70–75% of peak power) separated by a 6-min baseline rest (EX1 to EX2). During the protocol, a pulsed Doppler ultrasound technique was utilized to continuously measure the BF in the right femoral artery. The protocol was repeated at least 6 times to characterize the precise kinetics. In agreement with previous studies using cycling exercise, the O2 kinetics in the 2nd bout were facilitated compared with that in the 1st bout [mean ±S.D. of the ‘effective’ time constant (
): EX1, 68.6 ± 15.9, versus EX2, 58.0 ± 14.4 s. Phase II-: EX1, 48.7 ± 9.0, versus EX2, 41.2 ± 13.3 s. Empirical index of the slow component (
O2(6–3)): EX1, 78 ± 44, versus EX2, 57 ± 36 ml min–1 (P < 0.05)]. However, no substantial difference was observed for the facilitation of the femoral artery BF response to the 1st and 2nd exercise bouts [i.e. the ‘effective’ of the femoral artery BF: EX1, 40.8 ± 16.9, versus EX2, 39.0 ± 17.1 s (P > 0.05)]. It was concluded that the faster pulmonary O2 kinetics during heavy KE exercise following prior heavy exercise was not associated with a similar modulation in the BF to the working muscles.
(Received 24 September 2003;
accepted after revision 23 January 2004; first published online 17 February 2004)
Corresponding author Y. Fukuba: Department of Exercise Science and Physiology, School of Health Sciences, Hiroshima Prefectural Women's University, 1-1-71, Ujina-higashi, Minami-ku, Hiroshima 734–8558, Japan. Email: fukuba{at}hirojo-u.ac.jp
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