Lower extremity kinetics and muscle activation during gait are significantly different during and after pregnancy compared to nulliparous females.

BACKGROUND: Low back, pelvic, and lower extremity pain are common during and after pregnancy. Understanding differences in mechanics between pregnant and non-pregnant females is a first step toward identifying potential pathological mechanisms. The primary purpose of this study was to compare joint kinetics and muscle activation during gait between females during and after pregnancy to nulliparous females.

METHODS: Twenty pregnant females completed testing on three occasions (second trimester, third trimester, and post-partum), while 20 matched, nulliparous controls were tested once. Motion capture, force data, and surface electromyography were averaged across seven trials during gait. Lower extremity kinematics, lower extremity moments and work normalized to pre-pregnancy body mass, work distribution, and peak and average muscle activation amplitude were calculated. Independent t-tests were conducted between pregnant and nulliparous females at each time point.

RESULTS: Compared to controls, peak hip abductor moments were greater throughout and after pregnancy. Females in second trimester also demonstrated greater sagittal negative ankle work and greater percent contribution of the ankle and smaller percent contribution of the hip to negative work. Compared to controls, during third trimester there were greater knee abductor, ankle plantarflexor, and ankle dorsiflexor moments and greater work at the ankle and total work. Several moment and work variables continued to be elevated post-partum compared to controls. Gluteus maximus muscle activation amplitude was smaller in second trimester and post-partum compared to controls.

SIGNIFICANCE: While overall joint demands were greater during and after pregnancy, there was a smaller relative sagittal utilization of the hip early in pregnancy and smaller gluteus maximus muscle amplitude during second trimester and post-partum. Because the gluteus maximus muscle contributes to force closure and dynamic stability of the low back and pelvis, relative gluteus maximus disuse, concurrent with increased joint loads, could potentially contribute to pain during and after pregnancy.