Background: Among children, both cardiorespiratory fitness and relative weight have been shown to be associated with cognitive function, mental health, and self-concept. However, it is not well understood how different combinations of fitness and fatness are related to these outcomes. Purpose: This study investigates the impact of the Fit-Fat relationship on global self-worth and perceived athletic competence in children. Methods: Participants were 2134 children (50% M), with a mean age of 11.3 (SD=0.4). Participants completed body composition measures, the Leger Shuttle Run Test (VO2max) and the Harter GSW and AC subscales. Fit-fat was defined as VO2max/(waist/height). Four models were defined for each outcome; one for each predictor separately (VO2max, waist:height, fit-fat) and one with all three predictors. In the final model, variables were orthogonalized to measure the contribution of Fit-Fat beyond its constituent measures. Results: Fit-Fat (ß= .20, p < .001) and VO2max (ß= .19, p < .001) were equivalently associated with self-worth, while VO2max (ß = .34, p < .001) was superior to Fit-Fat (ß = .26, p < .001) as an indicator of athletic competence. Effects for waist:height were slightly weaker in both cases. For both outcomes, Fit-Fat made a small but significant contribution after effects of VO2max and waist:height were removed (self-worth: ß=0.04, p=0.05; competence, ß=0.05, p=0.01). Conclusion: While Fit-Fat is a useful indicator of self-worth and athletic competence, it is not superior to its constituent variables. However, it captures variance not accounted for by CRF or body composition measures, and is therefore of independent importance.
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