Research

Front & Back Muscle Slings Function Together

Front & Back Muscle Slings Function Together

Coordinated Rotation of the trunk
With a right sacroiliac lesion, the right internal oblique and left external oblique pull the rib cage anteriorly and inferiorly, while the right latissimus dorsi and left gluteus maximus pull the right shoulder posteriorly and inferiorly, simultaneously causing right lumbar 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. These movements would reciprocate with gait.

An important point to consider is Gracovetsky’s [1] analysis of shoulder counter rotation occurring during gait. When the left leg is in extension (pelvis rotating to the left with right gluteus maximus contracted), they found that the left shoulder would rotate to the right. The contracted muscles included the left pectoralis major, anterior deltoid and anterior serratus and the right trapezius, posterior deltoid and latissimus dorsi.

The sacroiliac lesion
However, with a right sacroiliac nutation lesion, in order to protect the right sacroiliac joint, the muscle groups that contribute to provide ipsilateral nutation, including the, right gluteus maximus-left latissimus dorsi and the left internal oblique-right external oblique combinations, would be chronically inhibited. Likewise, the muscles that provide right counternutation, including the right latissimus dorsi-left gluteus maximus and the right internal oblique-left external oblique combinations would be chronically contracted.

All of the shoulder muscles mentioned above would also be involved in a similar manner, depending on their action of promoting nutation or counternutation relative to the lesioned or normal (or less lesioned) side.  The muscles that rotate the shoulder to the right would be chronically contracted, while the same muscles on the opposite side would be chronically inhibited.

Over time, the muscles that promote counternutation will become tighter and overpower the inhibited ipsilateral muscles that promote nutation. This chronic contraction/inhibition pattern would 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.