Associations of 24‐hours activity composition with adiposity and cardiorespiratory fitness: The PregnActive project

Aim This study examined the associations of activity behaviors composition (sleep, sedentary time, light and moderate‐to‐vigorous physical activity) with adiposity and cardiorespiratory fitness, and how isotemporal reallocations of time between activity behaviors are associated with differences in adiposity and cardiorespiratory fitness. Methods A cross‐sectional study was conducted in 130 women during midpregnancy. Activity behaviors, conceptualized as a 24‐hours composition, were objectively assessed by multi‐sensor monitors. Skinfold thickness, fat mass index, and body mass index were calculated as indicators of adiposity. Cardiorespiratory fitness was assessed using a 6‐minute walk test. Log‐ratio multiple linear regression models and compositional isotemporal substitutions were used to analyze the associations and estimated differences in outcomes. Results The activity composition was significantly associated with adiposity indicators (all P < .001) and cardiorespiratory fitness ( P values from .025 to <.001) during midpregnancy. The isotemporal substitutions were asymmetrical, showing the highest estimated differences in adiposity (8.7%, 0.80 kg/m 2 , for fat mass index; 6.0%, 2.65 mm, for the sum of skinfold thickness; and 3.8%, 1.02 kg/m 2 , for body mass index) and cardiorespiratory fitness (3.0%, 1.00 mL/kg min) when 30 minutes of moderate‐to‐vigorous physical activity was reallocated by sedentary time. Conclusion The activity composition was associated with adiposity and the cardiorespiratory fitness levels during midpregnancy, with moderate‐to‐vigorous physical activity being the leading activity behavior. The most unfavorable differences in adiposity and cardiorespiratory fitness were found when moderate‐to‐vigorous physical activity was replaced by another behavior, mainly sedentary time, reinforcing the importance of at least maintaining moderate‐to‐vigorous physical activity during pregnancy.