Resumen de Aerobic Function and Muscle Deoxygenation Dynamics during Ramp Exercise in Children.
Melitta A. Mcnarry, Alan R. Barker, Colin Farr, Neil Armstrong, Andrew Middlebrooke, Deborah Welford, Brynmor C. Breese
AB Purpose: 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[spacing dot above]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[spacing dot above]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[middle dot]min-1, vs boys, 0.95 +/- 0.19 L[middle dot]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[middle dot]min-1, vs boys, 1.22 +/- 0.28 L[middle dot]min-1, P = 0.014). However, when expressed against relative work rate or V[spacing dot above]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[spacing dot above]O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V[spacing dot above]O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V[spacing dot above]O2 contributed 12% of the variance in peak V[spacing dot above]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[spacing dot above]O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.
