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 , for fat mass index; 6.0%, 2.65 mm, for the sum of skinfold thickness; and 3.8%, 1.02 kg/m , 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.