The thoracolumbar fascia (TLF) is a thick, strong sheet of a ligamentous type of connective tissue, which connects with, and covers, the muscles of the trunk, hips, and shoulders.
The normal function of the Gmax will be to exert a pulling action on the fascia, thereby tensing its lower end. You can see from the diagram below that there is a connection between the Gmax and the contralateral latissimus dorsi muscle by means of the posterior layer of the TLF.
Both of these muscles conduct the forces contralaterally (i.e. to the opposite side) during the gait cycle (via the posterior oblique sling), which then causes increased tension through the TLF. This function is very important for rotation of the trunk and for force closure stabilization of the lower lumbar spine and the SIJ.
The thoracolumbar fascia (TLF) and its connection to the Gmax
There is also a co-contraction of the deeper muscles of lumbar stability—i.e. the TVA and the multifidus. These muscles co-contract when you move a limb. As far as I am aware, there has been nothing published recently about the TVA and multifidus being specifically triggered by engagement of the Gmax.
However, I personally think that the TVA muscle definitely responds to Gmax contraction, and I suspect that the multifidus does too, as they all have an association with the sacrotuberous ligament of the pelvis (either directly or indirectly), which assists in force closure of the SIJ.
So it’s worth considering that if the Gmax is weak or misfires, its function of tensing the TLF is reduced, which will cause a natural overactivation of the contralateral latissimus and the ipsilateral multifidus, as well as stimulating other compensatory mechanisms.
John Gibbons is a qualified and registered osteopath with the General Osteopathic Council, specializing in the assessment, treatment, and rehabilitation of sport-related injuries. Having lectured in the field of sports medicine and physical therapy for over 12 years, John delivers advanced therapy training to qualified professionals within a variety of sports at elite level.