The purpose of this study was to examine the associations between physical activity (PA) and abdominal adiposity, as measured by waist circumference, in children and adolescents, and to test whether cardiovascular fitness (CVF) modifies these associations. PA components were measured by accelerometry in 1075 individuals aged 9 or 15 years old. CVF was measured by a maximal cycling test. Self-reported maternal educational level, body mass index, children’s birth weight and television viewing were used as confounders. Linear regression did not show any association between the PA variables and waist circumference, after controlling for sex, age and height. When stratifying by CVF level (low/high), time spent at vigorous PA was inversely associated with waist circumference in the low CVF group. Unexpectedly, in the high CVF group, the PA variables were positively associated with waist circumference. In both groups, the results were unchanged after controlling for the confounders. CVF was inversely associated with waist circumference, after controlling for all PA variables and confounders.
CVF is inversely associated with abdominal adiposity and seems to modify the associations between PA and abdominal adiposity. In low-fit children and adolescents, time spent in vigorous PA seems to be the key component linked to abdominal adiposity. This finding should be considered in further development of lifestyle intervention strategies.