Research

Internal - External Obliques Muscle Sling

Internal - External Obliques                                         Muscle Sling

The fascia of the right internal and left external obliques interdigitate at the linea alba to function as a unit in inducing counternutation on the side of the internal oblique and nutation on the side of the external oblique.

Front and back muscle slings function together: During normal movement, the Internal and External Obliques coordinate with the Gluteus Maximus and Latissimus Dorsi to provide trunk rotation.

In a counternutation response to a right sacroiliac lesion, the right internal oblique and left external oblique pull the left rib cage inferiorly and anteriorly, while the right latissimus dorsi and left gluteus maximus pull the right shoulder inferiorly and posteriorly, simultaneously causing right rotation coupled with right lateral flexion.

This coordinated movement results in counternutation on the right and nutation on the left and is consistent with Gracovetsky’s [1] analysis of muscular patterns in shoulder counter rotation occurring during gait, which includes, on the right, a tight trapezius and posterior deltoid but inhibited pectoralis major, anterior deltoid and anterior serratus, while on the left, it would include a tight pectoralis major, anterior deltoid and anterior serratus, but inhibited posterior deltoid and left trapezius.

With chronicity, as evident in a nutation lesion, these muscles remain in a state of tension throughout both nutation and counternutation, and reinforce this compensation pattern. Over time, this pattern may lead to structural distortions and coordination difficulties that may be expressed by delayed timing and reduced balance and performance throughout the body.

References:
1.    Gracovetsky, S. and H. Farfan, The optimum spine. Spine, 1984. 11(6): p. 543-73.