Muscle Function After Childbirth

Stability of the lumbar spine and pelvis is essential to nearly all activities of daily living, and is achieved primarily by muscular stabilization. Recent studies have shown that postpartum women are more fatigable than nulligravid women during fatiguing tasks with the lumbopelvic stabilizing muscles (23%) and the trunk flexor muscles (52%) at six months postpartum. Postpartum women also demonstrate impaired control of force with the trunk flexor muscles; however, it is unknown if force control during a fatiguing task of the lumbopelvic stabilizing muscles is impaired in postpartum women. This study has 3 purposes: (1) To quantify limb steadiness during fatiguing exercise of the lumbopelvic stabilizing muscles among nulligravid women and postpartum women; (2) to quantify muscle activity in the trunk, test limb and contralateral limb to provide insight into motor control; and (3) to identify possible factors (inter-recti distance (IRD), physical activity, pain, biopsychosocial factors) that contribute to neuromuscular function (fatigability and force control). This is a novel, translational study that, for the first time, will quantify lower extremity force control in postpartum women. As this has not been studied before, to the best of the investigators' knowledge, this proposal will be a pilot study to establish means to utilize in power analyses for future studies of larger magnitude. Furthermore, neuromuscular function is not typically assessed clinically in postpartum women, and no tests exist to easily assess fatigability of the lumbopelvic stabilizing muscles in clinic settings. This study will also provide further data to highlight the ASLR Fatigue Task as a possible clinical examination tool and outcome measure to assess fatigability of the lumbopelvic stabilizing muscles.