title: ATP economy of force maintenance in human tibialis anterior muscle.
abstract: OBJECTIVE
  The aim of this study was investigate ATP economy of force maintenance in the human tibialis anterior muscle during 60 s of anaerobic voluntary contraction at 50% of maximum voluntary contraction (MVC).
  
  
  METHODS
  ATP turnover rate was evaluated using P magnetic resonance spectroscopy (P-MRS). The total volume of ankle dorsiflexor muscles was assessed by H magnetic resonance imaging (MRI) (H-MRI), and the fiber type composition of the tibialis anterior muscle was evaluated using histochemical analysis of muscle biopsies.
  
  
  RESULTS
  The tibialis anterior muscle occupied 59.7 +/- 0.6% (mean +/- SEM) of the total ankle dorsiflexor muscle volume, which was 267 +/- 10 cm. Relative cross-sectional areas occupied by Type I, IIA, and IIB fibers in the tibialis anterior were 69.3 +/- 2.2, 27.4 +/- 2.76, and 3.2 +/- 1.0%, respectively. ATP economy of force maintenance did not change significantly during the 60-s contraction. It averaged at 4.81 +/- 0.42 N.s.micromol-1, and correlated with the relative cross-sectional area of the muscle occupied by Type I fiber (r = 0.73, P < 0.01). For the second half of the contraction, subjects dropping in force showed lower ATP economy compared with those maintaining the force (3.7 +/- 0.6 vs 5.3 +/- 0.6 N.s.micromol-1; P < 0.05).
  
  
  CONCLUSIONS
  It is argued that the unchanged ATP economy of force maintenance during the voluntary contraction could be due to an increase in the ATP economy of contracting muscle fibers offsetting the effects of increased temperature and low ATP economy of Type II fibers. Mechanical interaction between motor units could also act to improve ATP economy of force maintenance.
authors.affiliation: NMR Centre, Department of Medical Biochemistry and Genetics A, Panum Institute, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Yoshinao
authors.initials: Y
authors.lastname: Nakagawa
authors.forename: Aivaras
authors.initials: A
authors.lastname: Ratkevicius
authors.forename: Masao
authors.initials: M
authors.lastname: Mizuno
authors.forename: Bjorn
authors.initials: B
authors.lastname: Quistorff
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000502:physiology; D000293:Adolescent; D000328:Adult; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D007866:Leg; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D010725:Phosphocreatine; D015203:Reproducibility of Results; D019415:Torque
chemical_list: D010725:Phosphocreatine; D000255:Adenosine Triphosphate