Fatigability of the Lumbopelvic Stabilizing Muscles in Women 8 and 26 Weeks Postpartum

Abstract

Background: Pregnancy and childbirth are associated with lumbopelvic pain and instability. Fatigability of the lumbopelvic stabilizing muscles after childbirth is unknown, and no clinical tests exist to assess this important metric of muscle function.

Objectives: To compare fatigability of the lumbopelvic stabilizing muscles in postpartum and nulligravid (control) women using the Active Straight Leg Raise (ASLR) Fatigue Task, and to determine if fatigability is associated with inter-recti distance (IRD), physical function, and pain/disability.

Study design: Longitudinal case-control study.

Methods: Twenty-nine nulligravid (25.4 ± 9.1 years) and 31 postpartum women (31.4 ± 5.2 years; vaginal delivery n=18) were tested at two time points, 16 weeks apart (postpartum women tested at 8-10 and 24-26 weeks postpartum). Muscular function was assessed with manual muscle testing (MMT), the ASLR Test, and a new ASLR Fatigue Task. Other measures included IRD, rectus abdominis thickness, physical activity, and six-minute walk distance.

Results: Postpartum women were 23% more fatigable (p=0.028) and were weaker (MMT) (p<0.001) than controls up to 26 weeks postpartum. The ASLR fatigue task (time-to-failure) was associated with smaller IRD, greater rectus abdominis thickness, higher physical activity levels, greater MMT strength, and further distance walked in six minutes (p<0.05).

Conclusion: Postpartum women (up to 6 months) had greater fatigability of the lumbopelvic stabilizing muscles and lower physical function than nulligravid women, suggesting core muscle function and fatigability should be assessed after pregnancy and childbirth. The ASLR Fatigue Task could be a clinically useful tool to determine fatigability of the lumbopelvic stabilizing muscles in women postpartum.

Keywords: Abdominal muscles; pregnancy; women’s health.

FIGURE 1.

Overview of study design and subject participation. DXA= dual x-ray absorptiometry; MMT= Manual Muscle Testing; ASLR= Active Straight Leg Raise; PFDI= Pelvic Floor Distress Inventory; PGQ= Pelvic Girdle Questionnaire

FIGURE 2.

Fatigability of the lumbopelvic stabilizing muscles at both time points (8–10 weeks [Initial] and 24–26 weeks [Follow Up] postpartum) using the ASLR fatigue task. Postpartum women had shorter time-to-task failure than control women at both time points (A), with no difference between a vaginal and Cesarean delivery (B). Women with a positive ASLR test (reduced difficulty of lifting lower extremity when external compression provided to pelvis), did not differ in time-to-task failure compared with women with a negative ASLR test (no change in difficulty or lifting lower extremity with or without external compression to pelvis) (C).

FIGURE 3.

Longer time-to-task failure on the ASLR fatigue task was associated at both time points with lower body fat (A & B), smaller inter-recti distance (C & D), greater self-reported physical activity over the previous year (E & F), and thicker rectus abdominis muscle (G & H).