Understanding Abdominal and Core Muscles: Clearing the Confusion

When it comes to fitness and rehabilitation, the terms abdominal muscles and core are often used interchangeably, yet they represent different anatomical and functional concepts. This article clarifies the distinction, explains their respective roles, and provides evidence-based strategies for effective training.

1. Abdominal Muscles: Location, Attachments, and Function

The abdominal muscles rectus abdominis, external and internal obliques, Erector Spinae, Quadratus Lumborum,  Multifidus, and transverse abdominis are located on the front, sides and back of the abdomen. They attach to the thoracic cage, lumbar spine, and pelvis, and their primary role is to mobilize and stabilize the lumbar spine (Kendall et al., 2005).

A common misconception is that many “abdominal” exercises actually target the hip flexors—especially the iliopsoas—more than the abdominals. For example, traditional sit-ups or straight-leg raises recruit the iliopsoas heavily, particularly when the feet are anchored (Axler & McGill, 1997). The iliopsoas is a hip flexor, not a spinal flexor, although it indirectly affects lumbar spine posture (Neumann, 2010).

Research using electromyography (EMG) confirms that curl-ups with knees bent and feet unanchored better isolate the abdominals than sit-ups (Escamilla et al., 2006).

2. Core Muscles: A Bigger Picture

The core is more than just the abdominals—it includes all muscles that stabilize the spine, pelvis, and torso. This encompasses:

• Abdominal muscles

• Deep spinal stabilizers (multifidus, erector spinae)

• Diaphragm

• Pelvic floor muscles

• Hip stabilizers (gluteals, adductors, rotators)

The core’s primary function is to stabilize the thorax and pelvis during movement, support posture, and transfer force between the upper and lower body (Hodges & Richardson, 1996).

3. Functional Core Training and the Four Subsystems

Training the core effectively requires functional, integrated exercises that challenge stability in multiple planes of motion—not just isolated flexion.

These exercises activate four interconnected subsystems (Page et al., 2010):

Deep Stabilization Subsystem

Muscles: transverse abdominis, multifidus, diaphragm, pelvic floor

Function: Provides segmental spinal stability and intra-abdominal pressure

Posterior Oblique Subsystem

Muscles: gluteus maximus, latissimus dorsi, thoracolumbar fascia

Function: Generates rotational power, stabilizes in cross-body movements

Anterior Oblique Subsystem

Muscles: internal/external obliques, adductors, hip external rotators

Function: Stabilizes during twisting and side-bending

Deep Longitudinal Subsystem

Muscles: the erector spinae, biceps femoris, tibialis anterior, and fibularis longus, Thoracolumbar Fascia (Deep Posterior layer). It may also incorporate the piriformis, adductor magnus, and rhomboids,

Function: Contributes to stabilization of the tibiofibular joints, hip joints, sacroiliac joints, and all segments of the spine.

Lateral Subsystem

Muscles: gluteus medius, tensor fasciae latae, adductors

Function: Controls lateral stability during gait and single-leg tasks

Studies show that core stabilization programs using planks, bird-dogs, anti-rotation presses, and single-leg deadlifts improve trunk muscle thickness, proprioception, and reduce low back pain risk (Kavcic et al., 2004; Wang et al., 2021).

References (APA Style)

Axler, C. T., & McGill, S. M. (1997). Low back loads over a variety of abdominal exercises: Searching for the safest abdominal challenge. Medicine & Science in Sports & Exercise, 29(6), 804–811. https://doi.org/10.1097/00005768-199706000-00012

Escamilla, R. F., Babb, E., DeWitt, R., Jew, P., Kelleher, P., Burnham, T., … & Andrews, J. R. (2006). Electromyographic analysis of traditional and nontraditional abdominal exercises: Implications for rehabilitation and training. Journal of Orthopaedic & Sports Physical Therapy, 36(1), 45–57. https://doi.org/10.2519/jospt.2006.2016

Hodges, P. W., & Richardson, C. A. (1996). Inefficient muscular stabilization of the lumbar spine associated with low back pain. Spine, 21(22), 2640–2650. https://doi.org/10.1097/00007632-199611150-00014

Kavcic, N., Grenier, S., & McGill, S. M. (2004). Quantifying tissue loads and spine stability while performing commonly prescribed low back stabilization exercises. Spine, 29(20), 2319–2329. https://doi.org/10.1097/01.brs.0000142222.14387.97

Kendall, F. P., McCreary, E. K., Provance, P. G., Rodgers, M. M., & Romani, W. A. (2005). Muscles: Testing and Function with Posture and Pain (5th ed.). Lippincott Williams & Wilkins.

Neumann, D. A. (2010). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation (2nd ed.). Mosby Elsevier.

Page, P., Frank, C. C., & Lardner, R. (2010). Assessment and Treatment of Muscle Imbalance: The Janda Approach. Human Kinetics.

Wang, X. Q., Zheng, J. J., Yu, Z. W., Bi, X., Lou, S. J., Liu, J., … & Chen, B. L. (2021). A meta-analysis on the efficacy of core stability exercise in chronic low back pain. PloS One, 7(12), e52082. https://doi.org/10.1371/journal.pone.0052082