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Effects of a prior high‐intensity knee‐extension exercise on muscle recruitment and energy cost: a combined local and global investigation in humans
Author(s) -
Layec Gwenael,
Bringard Aurélien,
Le Fur Yann,
Vilmen Christophe,
Micallef JeanPaul,
Perrey Stéphane,
Cozzone Patrick J.,
Bendahan David
Publication year - 2009
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2008.044651
Subject(s) - anaerobic exercise , deoxygenation , intensity (physics) , medicine , exercise intensity , isometric exercise , chemistry , cardiology , apparent oxygen utilisation , motor unit recruitment , oxidative phosphorylation , endocrinology , exercise physiology , electromyography , heart rate , physical therapy , oxygen , biochemistry , physical medicine and rehabilitation , blood pressure , physics , quantum mechanics , catalysis , organic chemistry
The effects of a priming exercise bout on both muscle energy production and the pattern of muscle fibre recruitment during a subsequent exercise bout are poorly understood. The purpose of the present study was to determine whether a prior exercise bout which is known to increase O 2 supply and to induce a residual acidosis could alter energy cost and muscle fibre recruitment during a subsequent heavy‐intensity knee‐extension exercise. Fifteen healthy subjects performed two 6 min bouts of heavy exercise separated by a 6 min resting period. Rates of oxidative and anaerobic ATP production, determined with 31 P‐magnetic resonance spectroscopy, and breath‐by‐breath measurements of pulmonary oxygen uptake were obtained simultaneously. Changes in muscle oxygenation and muscle fibre recruitment occurring within the quadriceps were measured using near‐infrared spectroscopy and surface electromyography. The priming heavy‐intensity exercise increased motor unit recruitment ( P < 0.05) in the early part of the subsequent exercise bout but did not alter muscle energy cost. We also observed a reduced deoxygenation time delay, whereas the deoxygenation amplitude was increased ( P < 0.01). These changes were associated with an increased oxidative ATP cost after ∼50 s ( P < 0.05) and a slight reduction in the overall anaerobic rate of ATP production (0.11 ± 0.04 m m min −1 W −1 for bout 1 and 0.06 ± 0.11 m m min −1 W −1 for bout 2; P < 0.05). We showed that a priming bout of heavy exercise led to an increased recruitment of motor units in the early part of the second bout of heavy exercise. Considering the increased oxidative cost and the unaltered energy cost, one could suggest that our results illustrate a reduced metabolic strain per fibre.