Muscles in the body rarely (if ever) work individually. When one muscle shortens, the opposing muscle has to lengthen. When a muscle contracts, it typically tugs on a bone, which has an effect on all the other muscles attached to that bone. Additionally, the muscles are interlaced and connected with fascia. Fascia is a densely woven structure that covers and interpenetrates all structures of the body (nerves, blood vessels, bone, muscles, and internal organs).
There are four diagonal slings that influence movement of the spine, shoulders, and pelvis. The anterior (front) oblique slings run from right shoulder to left hip and left shoulder to right hip, forming an X across the front of the torso. For the nerds out there who want more detail, specifically left serratus anterior, left external oblique, crossing midline to right internal oblique into right adductor (picture on left). The posterior oblique slings run from right shoulder to left hip, left shoulder to right hip in the back, forming an X in the back. The left latissimus dorsi, thoracolumbar fascia, right gluteus medius and right ITBand make up the back X. There are many functional applications of the diagonal slings, beauty sashes, if you will. Listed below are a few examples of home exercises that utilize the oblique slings to stabilize and/or mobilize the spine.
From a bridge with feet on floor/couch/step/chair/wall:
Float right leg to table top, acknowledge the sling/connection from right shoulder to left hip in the back holding your pelvis off the ground. 10-30 reps on the right, 10-30 on left. Alternate right/left for second set of 10-30 each side.
--if your feet are on a higher, you can bridge higher and mobilize the upper back. With feet lower, the legs work harder to heave that pelvis off the floor.
In sitting on ball/on floor/on hippity hop:
Hug a tree, tip pubic bone towards nose to round the spine backwards. Rotate right arm to the right. Bring right hand back to midline while returning to seated position. Sling/connection from right hand to left hip (possibly even foot) works to pull back to sitting and left shoulder to right hip keeps your head from hitting the floor (please avoid hitting the floor at all costs). 10-30 reps on the right, then 10-30 with the left arm. Second set, alternate right/left for 10 reps each side.
From plank with hands on step/bathtub/couch/counter/floor:
Press pelvis up and backwards into pike position while floating right leg towards ceiling. Sling from left shoulder to right heel in the back raises the leg, right shoulder to left hip in front presses hips high.
--if your hands are on a lower surface/floor, it's much more stretchy and a little harder to find the slings. Recommend hands higher to start, then lower then hands once you find the slings in your bod.