Factors Contributing to the Energy Expenditure of Youth during Cycling and Running

This study evaluated factors that contribute to the increased energy cost of locomotion in youth. The subjects were 321 8-18-year-old youth, similar dispersed by age and sex. Oxygen uptake (VO 2 ) was measured during rest (REE), running at 8 km · h −1 and cycling at 16 km · h −1 , using a COSMED K4b 2 metabolic system. Developmental stage was obtained via questionnaire. Stature, body mass, and skinfolds (triceps & subscapular) were measured. Both sexes had similar absolute VO 2 (mL · min −1 ) at rest ( p = 0.065) and running ( p = 0.084), but the males had a higher VO 2 during cycling ( p = 0.046). There were no sex differences in relative VO 2 (mL · kg −1 · min −1 ) at rest ( p = 0.083); however, the males had a higher VO 2 than the females during cycling and running ( p £ 0.002). Multiple regression, tested for collinearity, found that absolute VO 2 during cycling and running was mostly related to fat-free mass ( p = 0.0001). Similar analyses for relative VO 2 (mL · kg −1 · min −1 ) during cycling found that fat-free mass, sex, and skinfolds were significant contributors (p ‡ 0.003). During running the relative VO 2 was related to skinfolds, fat-free mass, and resting energy expenditure ( p < 0.05). Neither age nor developmental stage was a significant contributor. The results indicate that the VO 2 of locomotion is most closely associated with fat-free mass. Thus, to compare youth of varying age or pubertal developmental status, fat-free mass should be taken into consideration.