Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2006) 05, 254 - 265

Research article
Influence of Posture on Pulmonary O Uptake Kinetics, Muscle Deoxygenation and Myolectrical Activity During Heavy-Intensity Exercise
Romain Denis, Stéphane Perrey 
Author Information
Motor Efficiency and Deficiency EA 2991, Faculty of Sport Sciences, University of Montpellier I, 34090 Montpellier, France

Stéphane Perrey
✉ Faculté des sciences du sport, EA 2991 Efficience et Déficience Motrices, 700 avenue du pic saint loup, 34090 Montpellier, France.
Email: stephane.perrey@univ-montp1.fr
Publish Date
Received: 08-02-2006
Accepted: 19-04-2006
Published (online): 01-06-2006
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ABSTRACT

The aim of the present study was to test the hypothesis that compared to upright posture, slower oxygen uptake (VO2) kinetics resulting from exercise at the same relative metabolic load in the supine posture will be associated with increased muscle de-oxygenation and greater myoelectrical activity. Nine subjects completed one 12-min heavy-intensity constant-load exercises in each of the supine and upright postures on an electronically braked cycle ergometer at a same gain in metabolism per unit increase in work intensity (10.8 ± 1.3 vs. 11.8 ± 1.1 mlO2·min-1·W-1 in upright and supine, respectively) on separate days. Breath-by-breath VO2 kinetics were analyzed with a double exponential model to characterize the primary and slow component phases. Myoelectrical activity (RMS) of the vastus lateralis (VL), rectus femoris, and biceps femoris muscles was recorded at different epochs of the exercise. Oxygenation of the VL muscle was recorded continuously by near-infrared spectroscopy. In supine compared with upright cycling, the primary time constant of VO2 kinetics was significantly increased (32.7 ± 10.7 s vs. 23.5 ± 6.7 s, respectively) while the absolute magnitude of VO2 slow component was decreased (p < 0.05) but not the relative amplitude. VL de-oxygenation was higher (p < 0.05) in supine cycling throughout the exercising period whereas RMS values for all muscles did not change appreciably over time. Our findings suggest that lowered oxygen supply induced by supine heavy exercise, alters oxidative metabolism dynamics and increases muscle de-oxygenation. However, cycling supine did not increase markedly the rate of muscle fatigue.

Key words: muscle perfusion, heavy cycling exercises, NIRS, VO slow component


           Key Points
  • Hydrostatic pressure gradients in blood vessels oriented longitudinally in the body are lesser in supine than in upright posture.
  • Lowered oxygen supply induced with supine exercise slows oxidative metabolism dynamics and increases muscle de-oxygenation during heavy exercise.
  • Compared to upright, supine exercise did not increase markedly the rate of muscle fatigue at a same relative metabolic load.
 
 
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