Free-living sit-to-stand angular velocity derived from thigh-worn accelerometry slows during pregnancy, but is not associated with binary self-reported discomfort prevalence.

BACKGROUND: The sit-to-stand transition is a key movement influenced by coordination, balance, and lower-limb strength. While laboratory-based studies show slower sit-to-stand angular velocity during pregnancy, free-living sit-to-stand angular velocity and its relationship to pregnancy-related discomforts remain unclear. PURPOSE: This study examined differences between the second and third trimesters of pregnancy in free-living sit-to-stand angular velocity, movement behaviours, and discomfort frequency, and assessed whether changes in sit-to-stand angular velocity predicted discomfort changes. METHODS: Pregnant participants (n = 176) from the PRECISE Occupational Cohort in Denmark wore thigh-worn accelerometers for ∼one week during the second and third trimesters to measure sit-to-stand transitions, step counts, and movement behaviours. Weekly questionnaires reported the presence of lower back pain, pelvic pain, Braxton-Hicks contractions, fatigue, and lower-limb edema. RESULTS: Linear mixed models compared second and third trimesters, and regression models tested whether sit-to-stand angular velocity change predicted discomfort change, adjusting for age and pre-pregnancy body mass index. Median (d=-0.53) and 90th percentile sit-to-stand angular velocity (d=-0.47) were significantly lower in the third trimester, accompanied by fewer daily sit-to-stand angular transitions (d=-0.14) and reductions in step count (d=-0.29), standing time (d=-0.21), and moderate-to-vigorous physical activity (d=-0.43; all, p < 0.001). Pregnancy-related discomforts increased in frequency (p < 0.001), with pelvic pain (odds ratio (OR)= 5.02), Braxton-Hicks contractions (OR=17.9), and lower-limb edema (OR=9.23) showing the largest rises. Changes in median and 90th percentile sit-to-stand angular velocity were not associated with changes in the composite weekly discomforts (both, p > 0.235). CONCLUSION: Free-living sit-to-stand angular velocity declines and discomfort prevalence rises between the second and third trimesters.