Author(s): PELLERINE, L., NØRTOFT FRANKEL, H., MØLENBERG BEGTRUP, L., O’BRIEN, M., SVARTEGREN, M., HETTIARACHCHI, P., Institution: DALHOUSIE UNIVERSITY, Country: CANADA, Abstract-ID: 776

INTRODUCTION:
The sit-to-stand transition is a key daily movement influenced by coordination, balance, and lower-limb strength. There are biomechanical changes to the sit-to-stand transition during pregnancy due to increased abdominal mass. The rapid biomechanical changes during pregnancy can often lead to more frequent pain and fatigue during daily physical activities. While laboratory-based studies show slower sit-to-stand angular velocity during pregnancy, the changes in free-living sit-to-stand angular velocity and their relationship to pregnancy-related discomforts remains unclear. This study examined differences between the second and third trimesters of pregnancy in free-living sit-to-stand angular velocity and discomfort frequency, and assessed whether changes in sit-to-stand angular velocity predicted discomfort changes.
METHODS:
Pregnant participants (n=176; mean age: 31.2 ± 4.1 years) 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 (e.g., sedentary time, standing time, physical activity levels). Weekly text message questionnaires assessed for the presence of lower back pain, pelvic pain, Braxton-Hicks contractions, fatigue, and lower-limb edema throughout the second and third trimesters. Linear mixed models compared the second and third trimesters, and regression models tested whether sit-to-stand angular velocity change predicted the changes in weekly discomforts. All regression models were adjusted for age and pre-pregnancy body mass index.
RESULTS:
Median (d=-0.53) and 90th percentile sit-to-stand 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). All pregnancy-related discomforts increased in weekly recurrences (p<0.001), with pelvic pain (OR=5.02), Braxton-Hicks contractions (OR=17.9), and lower-limb edema (OR=9.23) showing the largest rises in weekly occurrences. Changes in median and 90th percentile sit-to-stand angular velocity were not associated with changes in the total number of weekly discomforts (both, p>0.235).
CONCLUSION:
Free-living sit-to-stand angular velocity declines and discomfort prevalence both rise between the second and third trimesters, yet these changes appear independent of each other. Based on our results, the magnitude of the reduction in sit-to-stand velocity did not predict a change in the number of pregnancy-related discomforts. These findings highlight both the value and the challenge of free-living performance measures in characterizing mobility during pregnancy.