title: Aerobic Function and Muscle Deoxygenation Dynamics during Ramp Exercise in Children.
abstract: OBJECTIVE
  This study aimed to characterize changes in deoxyhemoglobin ([HHb]) response dynamics in boys and girls during ramp incremental exercise to investigate whether the reduced peak oxygen uptake (peak V˙O2) in girls is associated with poorer matching of muscle O2 delivery to muscle O2 utilization, as evidenced by a more rapid increase in [HHb].
  
  
  METHODS
  Fifty-two children (31 boys, 9.9 ± 0.6 yr, 1.38 ± 0.07 m, 31.70 ± 5.78 kg) completed ramp incremental exercise on a cycle ergometer during which pulmonary gas exchange and muscle oxygenation parameters were measured.
  
  
  RESULTS
  When muscle [HHb] was expressed against absolute work rate and V˙O2, girls had an earlier change in [HHb], as evidenced by the lower c/d parameter (girls, 54 ± 20 W, vs boys, 67 ± 19 W, P = 0.023; girls, 0.82 ± 0.28 L·min(-1), vs boys, 0.95 ± 0.19 L·min(-1), P = 0.055) and plateau (girls, 85 ± 12 W, vs boys, 99 ± 18 W, P = 0.031; girls, 1.02 ± 0.25 L·min(-1), vs boys, 1.22 ± 0.28 L·min(-1), P = 0.014). However, when expressed against relative work rate or V˙O2, there were no sex differences in ([HHb]) response dynamics (all P > 0.20). Significant correlations were observed between absolute and fat-free mass normalized peak V˙O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V˙O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V˙O2 contributed 12% of the variance in peak V˙O2 after adjusting for fat-free mass, gas exchange threshold, and body fatness (model R2 = 0.81, P < 0.001).
  
  
  CONCLUSIONS
  The sex difference in peak V˙O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.
authors.affiliation: 1A-STEM, College of Engineering, Swansea University, Swansea, UNITED KINGDOM; 2Medical Research Council Epidemiology Unit, Princess of Wales Hospital, Ely, UNITED KINGDOM; 3Children's Health and Exercise Research Centre, Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, UNITED KINGDOM; 4Bishop Burton College, Beverly, UNITED KINGDOM; and 5Centre for Research in Translational Biomedicine, School of Biomedical and Healthcare Sciences, Plymouth University, Plymouth, UNITED KINGDOM.
authors.forename: Melitta A
authors.initials: MA
authors.lastname: McNarry
authors.forename: Colin
authors.initials: C
authors.lastname: Farr
authors.forename: Andrew
authors.initials: A
authors.lastname: Middlebrooke
authors.forename: Deborah
authors.initials: D
authors.lastname: Welford
authors.forename: Brynmor
authors.initials: B
authors.lastname: Breese
authors.forename: Neil
authors.initials: N
authors.lastname: Armstrong
authors.forename: Alan R
authors.initials: AR
authors.lastname: Barker
mesh_terms: D002648:Child; D015444:Exercise / Q000502:physiology*; D005260:Female; D006339:Heart Rate; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010101:Oxygen Consumption; D011659:Pulmonary Gas Exchange; D012727:Sex Characteristics; D019265:Spectroscopy, Near-Infrared
chemical_list: D006454:Hemoglobins; C100003:deoxyhemoglobin