Is the Function of the Core Muscles Affected During Pregnancy?
Researchers in Turkey utilized surface electromyography (EMG) and ultrasound to understand the changes in core muscle morphology and activation during the last two trimesters of pregnancy.
Study Design: Descriptive cross-sectional study using surface EMG and 2D/3D ultrasound imaging.
Population: Sixty-seven primigravida women from a university hospital obstetrics clinic in Turkey. Participants ranged from 18 to 42 years old (mean age: 26 years) and mean BMI of 26.17 kg/m². Forty-one women were in their second trimester and 26 in their third trimester at the time of assessment.
Inclusion Criteria: Women at 14+ weeks gestation with singleton pregnancies.
Exclusion Criteria: Women with pregnancy complications (hypertension, preeclampsia, gestational diabetes), neurological disease, severe low back pain, or psychiatric illness were excluded.
Methods: Researchers measured core muscle function during pelvic floor contraction and at rest.
EMG: Electrodes were placed on the rectus abdominis, transversus abdominis (TA), external oblique (EO), internal oblique (IO), multifidus, and diaphragm—with electrode placement verified by ultrasound since anatomical landmarks shift as pregnancy progresses.
Ultrasound: Measured muscle thickness, diastasis recti distance at three levels, levator hiatus dimensions, and puborectal area. Fetal measurements were also taken to estimate the weight of the fetus.
Pelvic floor strength/coordination via digital palpation and scored using the PERFECT system.
Results:
Researchers found no correlations between core and pelvic floor muscles on EMG or ultrasound, suggesting disruption of normal co-activation patterns during pregnancy.
As fetal weight increased, IO and upper rectus thickness decreased, while EO and rectus EMG activity increased.
In the third trimester, EMG activity increased (although not significantly) across all core muscles during both pelvic floor contraction and rest.
Ultrasound revealed significant decreases in EO and IO thickness in the third trimester compared to the second (p=0.007 and p=0.009 during contraction; p=0.017 and p=0.001 at rest).
Diastasis recti increased significantly at all levels as pregnancy progressed (p<0.05).
PERFECT scores for endurance and fast contractions differed significantly between trimesters (p<0.01 and p=0.004) with the scores increasing as fetal weight increased.
Discussion/Clinical Implications:
Pregnancy appears to disrupt the coordinated co contraction pattern we see in non-pregnant women.
The abdominal muscles are working harder (increased EMG activity) while getting thinner. This supports the rationale for prenatal core training programs, not just for women with pain, but potentially for all pregnant women to maintain muscle coordination.
The authors suggest that exercise programs targeting core muscle co-contractiona may help prevent dysfunction that extends beyond pregnancy.
Çiçek, S., Çeliker Tosun, Ö., Parlas, M., Bilgiç, D., Yavuz, O., Kurt, S., Başer Seçer, M., & Tosun, G. (2023). Is the function of the core muscles affected during pregnancy? International Urogynecology Journal, 34, 2725–2736. https://doi.org/10.1007/s00192-023-05597-z
Differences in Abdominal and Lumbar Muscle Thickness and Contractile Function Between Nulliparous, Primiparous, and Multiparous Women 6 Months Postpartum
Researchers in Spain used ultrasound imaging to compare primiparous and multiparous women (both at 6 months postpartum) to nulliparous controls to answer:
Whether abdominal and lumbar muscles recover to “normal” by 6 months postpartum
Whether having multiple pregnancies affects the muscle thickness and contractile properties of the abdominal and lumbar muscles
Study Design: Cross-sectional observational study.
Population: Eighty women: 26 nulliparous, 29 primiparous, and 25 multiparous all assessed at 6 months postpartum for the parous groups. Mean age was 33.9 years across groups with no significant differences in age, weight, BMI, or waist circumference.
Exclusion criteria: Women with cesarean delivery, spinal/abdominal surgery, or neuromuscular disease were excluded.
Intervention/Methods:
Ultrasound Measurements:
Muscle thickness of the TA, IO, EO and multifidus at rest and during the abdominal draw-in maneuver (ADIM).
Contractile function was calculated as a thickness ratio (thickness during activation divided by thickness at rest).
Interrectus distance was measured at supraumbilical and infraumbilical locations.
Abdominopelvic function was assessed via prone bridge, supine bridge, and side bridge tests.
Results:
At rest, researchers reported no statistical difference in TA thickness between the nulliparous, primiparous, and multiparous groups at 6 months postpartum. They did notice that the IO and EO were significantly thinner in the parous groups when compared to the nulliparous group. However, there was no statistical significance in IO and EO thickness between the primiparous and multiparous groups.
All groups showed expected muscle thickness patterns (IO>EO>TA), with nulliparous and primiparous women demonstrating significant differences between all muscle layers. Multiparous women, however, only showed significant differences between TA and the obliques—not between IO and EO.
Unsurprisingly, interrectus distance was significantly greater in postpartum women at both measurement sites (p<0.01) multiparous showing greater supraumbilical interrectus distance than primiparous.
For the surprising part: Contractile function (thickness ratio) showed no significant differences between groups. All groups demonstrated the same functional pattern from greatest contraction to least (TrA> IO > EO). Despite being structurally thinner, the postpartum muscles contracted proportionally the same as nulliparous muscles.
Clinical Implications:
This study offers some key take aways for patients
At 6 months postpartum, abdominal muscles remain thinner than pre-pregnancy norms, but they’re functionally competent. The muscles can do their job even if they haven’t fully recovered their thickness. This is valuable information for patient education—structure and function don’t always move in lockstep.
The lack of difference between primiparous and multiparous women for contractile function suggests parity doesn’t compound functional deficits, though multiparous women did show greater diastasis. The authors note that individualized physical therapy interventions may still be warranted to fully restore thickness, particularly beyond 6 months.
Fuentes-Aparicio, L., Pérez-Alenda, S., Carrasco, J. J., Valls-Donderis, B., Dueñas, L., & Balasch-Bernat, M. (2024). Differences in abdominal and lumbar muscle thickness and contractile function between nulliparous, primiparous, and multiparous women 6 months postpartum. Physical Therapy, 104(12), pzae141. https://doi.org/10.1093/ptj/pzae141
Back to Our Patient
The relationship between her pelvic floor and abdominal muscles is likely disrupted. Exercises targeting co-contraction of these muscle groups may help restore coordination. Exercises targeting the anterior oblique sling can be helpful here.
This could look like:
In quadruped: Performing adductor isometrics with a pilates ball/yoga block while activating TA.
In ½ kneel: chops with medicine ball
Either stationary or with lateral walk outs: Paloff presses
Looking ahead to her postpartum recovery, early oblique integration may be beneficial. While TA function typically returns to nulliparous levels by 6 months post-vaginal delivery, the obliques take longer to recover.