title: ATP cost of muscle contraction is associated with motor unit discharge rate in humans.
abstract: Although a neural component has been suggested to contribute to the energetic cost of muscle contraction in vivo, the association between neural and energetic factors has not been determined during voluntary contractions in humans. Twenty young (24±1years, 10 women) healthy individuals performed isometric ankle dorsiflexion contractions at 20%, 50% and 100% of maximal voluntary contraction torque on two occasions during which measures of either motor unit discharge rates (MUDR, by indwelling electromyography) or ATP cost of contraction (by (31)P magnetic resonance spectroscopy) were obtained. Both MUDR and ATP cost increased with increasing contraction intensity (p≤0.02). A strong, positive relationship (r(2)=0.70; p<0.001) was observed between MUDR and ATP cost. These results suggest that a substantial portion of the variability in ATP cost can be explained by MUDR, and thus demonstrate that motor unit rate coding is likely an important neural factor contributing to energetic cost in vivo.
authors.affiliation: Department of Kinesiology, University of Massachusetts, Amherst, United States; Department of Human Physiology, University of Oregon, United States.
authors.forename: Anita D
authors.initials: AD
authors.lastname: Christie
authors.affiliation: Department of Kinesiology, University of Massachusetts, Amherst, United States.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Foulis
authors.affiliation: Department of Kinesiology, University of Massachusetts, Amherst, United States. Electronic address: jkent@kin.umass.edu.
authors.forename: Jane A
authors.initials: JA
authors.lastname: Kent
mesh_terms: D000200:Action Potentials; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D055815:Young Adult
chemical_list: D000255:Adenosine Triphosphate
keywords: Bioenergetics; Electromyography; Magnetic resonance spectroscopy; Metabolism; Motor unit; Rate coding