The POS works synergistically with the DLS. As illustrated in Figure 2.15, both the gluteus maximus and latissimus dorsi have attachments to the thoracolumbar fascia, which connects to the sacrum whose fibers run perpendicular to the sacroiliac joint. Thus, when the contralateral gluteus maximus and latissimus dorsi contract, a stabilizing force is transmitted across the sacroiliac joint.50 Just prior to heel strike, the latissimus dorsi and the contralateral gluteus maximus are eccentrically loaded. At heel strike, each muscle accelerates their respective limb (through its concentric action) and creates tension across the thoracolumbar fascia. This tension also assists in stabilizing the sacroiliac joint. Thus, when an athlete sprints, the POS transfers forces from the transverse plane orientation to the sagittal plane providing propulsion. The POS is also of prime importance for rotational activities such as swinging a golf club, a baseball bat, or throwing a ball.48,49,53 Dysfunction of any structure in the POS can lead to sacroiliac joint instability and low back pain. The weakening of the gluteus maximus or the latissimus dorsi can lead to increased tension in the hamstring—a factor in recurrent hamstring strains.47,50,53 If performed in isolation, squats for the gluteus maximus and pull downs or pull ups for the lats will not adequately prepare the posterior oblique system to perform optimally during athletic activities.
