Associations Between 24-Hour Movement Behaviors and Body Weight in Postpartum Women: An Isotemporal Substitution Model Approach

Background/Objectives: There are limited data on the dynamic changes in daily composition of movement behaviors (sleep, moderate to vigorous physical activity; MVPA, light physical activity; LPA, and sedentary time; SED) and their associations with body weight in postpartum women. The purpose of this study was to examine associations of reallocating time in one behavior to an-other with body weight at different times in the first year postpartum. Methods: The study included 86 women who delivered a singleton infant at ≥ 37 weeks gestation. Physical activity and sleep were measured via actigraphy in early, mid, and late postpartum. Body weight was measured at each timepoint. Isotemporal substitution models were used to examine the association of reallocating ten minutes of one behavior (MVPA, LPA, SED, or sleep) to another on body weight. Results: Participants spent most of their day in SED (~52-53%), followed by sleep (~30%), LPA (~12-13%), and then MVPA (~2%) throughout the first year postpartum. In early and mid-postpartum, but not late postpartum, reallocating 10 minutes of MVPA to LPA, SED, or sleep was associated with lower body weight (Range: 3.07-4.03 kg lower). In early and late postpartum, reallocating 10 minutes of SED to LPA was associated with a lower body weight (4.03kg and 1.04kg, respectively). In participants who slept ≥ 7 hours per day, reallocating sleep to LPA in early postpartum, and MVPA time to LPA in mid postpartum was associated with lower body weight. In those who slept < 7 hours, no significant associations with body weight were found when reallocating time from one behavior to another. Conclusions: Encouraging LPA throughout the post-partum period may be beneficial for weight loss and having enough sleep may be especially important for early to mid-postpartum. Future research examining the impact of changes in LPA on body weight in the postpartum period are needed along with postpartum specific 24h-hour movement guidelines.