title: Quadriceps muscle energetics during incremental exercise in children and adults.
abstract: OBJECTIVE
  This study tested the hypothesis that the muscle metabolic responses of 9- to 12-yr-old children and young adults during incremental quadriceps exercise are dependent on age and sex.
  
  
  METHODS
  Fifteen boys, 18 girls, 8 men, and 8 women completed a quadriceps step-incremental test to exhaustion inside a magnetic resonance scanner for determination of the muscle metabolic responses using P-magnetic resonance spectroscopy. Quadriceps muscle mass was determined using magnetic resonance imaging scans enabling comparison of metabolic data at a normalized power output.
  
  
  RESULTS
  The power output and the energetic state at the Pi/PCr and pH intracellular thresholds (IT) were independent of age and sex. The rate of change in Pi/PCr against power output after the ITPi/PCr (S2) was lower in boys (0.158 +/- 0.089) and girls (0.257 +/- 0.110) compared with men (0.401 +/- 0.114, P < 0.001) and women (0.391 +/- 0.133, P = 0.014), respectively, with sex differences present for children only (P = 0.003). Above the ITpH, S2 was more rapid in the men (-0.041 +/- 0.022, P = 0.003) and girls (-0.030 +/- 0.013, P = 0.011) compared with boys (-0.019 +/- 0.007), with no differences between the girls and the women (-0.035 +/- 0.015, P = 0.479). The increase in Pi/PCr at exhaustion was lower in boys (0.85 +/- 0.38) than that in men (1.86 +/- 0.65, P < 0.001) and in girls (1.78 +/- 1.25) than that in women (4.97 +/- 3.52, P = 0.003), with sex differences in both the child (P = 0.005) and the adult groups (P = 0.019).
  
  
  CONCLUSIONS
  During moderate-intensity exercise, muscle metabolism appears adult-like in 9- to 12-yr-old children, although both age- and sex-related differences in the "anaerobic" energy turnover are present during high-intensity exercise.
authors.affiliation: Children's Health and Exercise Research Centre, School of Sport and Health Sciences, University of Exeter, Exeter, United Kingdom.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Barker
authors.forename: Joanne R
authors.initials: JR
authors.lastname: Welsman
authors.forename: Jonathan
authors.initials: J
authors.lastname: Fulford
authors.forename: Deborah
authors.initials: D
authors.lastname: Welford
authors.forename: Neil
authors.initials: N
authors.lastname: Armstrong
mesh_terms: D000328:Adult; D000367:Age Factors; D015308:Anaerobic Threshold / Q000502:physiology; D002648:Child; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D010710:Phosphates / Q000378:metabolism; D010807:Physical Endurance / Q000502:physiology*; D052097:Quadriceps Muscle / Q000378:metabolism*; D012737:Sex Factors; D055815:Young Adult
chemical_list: D010710:Phosphates