Effect modification of cardiorespiratory fitness, obesity, and physical activity in adults.

We investigated if cardiorespiratory fitness modifies the association between obesity and the level of physical activity. In this cross-sectional study, we analyzed data from 746 adults, free of diagnosed cardiorespiratory or locomotor diseases. We analyzed sociodemographic and clinical information, cardiovascular risk factors, cardiorespiratory fitness, anthropometry, and level of physical activity (time spent in moderate-to-vigorous physical activity). Those that spent more time in moderate-to-vigorous physical activity were younger, male, with lower body mass index, without self-reported arterial blood hypertension, diabetes and dyslipidemia, non-smokers, and presented with better cardiorespiratory fitness. The linear regression coefficients showed that cardiorespiratory fitness changes according to the level of physical activity and body mass index (obesity in low cardiorespiratory fitness: β 6.0, p = 0.213, 95%CI -3.5 to 15.6; in intermediate cardiorespiratory fitness: β 6.3, p = 0.114, 95%CI -1.5 to 14.2; in high cardiorespiratory fitness: β -6.3, p = 0.304, 95%CI -18.4 to 5.8). This effect modification trend was present after adjusting the model by covariates. Cardiorespiratory fitness potentially modifies the association between body mass index and the level of physical activity. It should be routinely assessed to identify persons with overweight/ obesity with low/ intermediate cardiorespiratory fitness to prescribe individualized training.