This movement works the muscles of the back used to bring the arm down (against resistance) from an abducted position, to adduct the arm (move in towards the side of the body). This is a good exercise for training good posture and core stability, during the movement of the shoulder blade and arm. Along with the lower and mid traps, pectoralis major, rhomboids, and serratus anterior, the latissimus dorsi moves the shoulder blade down and inward as it pulls the arm down and in. This action will reinforce good movement patterns to keep the shoulder joint and soft tissues healthy.

The latissimus dorsi connects to the spine and pelvis through a strong layer of connective tissue, called the thoracolumbar fascia. Interestingly, the thoracolumbar fascia also attaches to the gluteus maximus, traps, and hamstrings. This connection ties in with the stability of the shoulder to the spine, the pelvis and the hips. The latissimus dorsi can pull the arm down and back, pull the arm in towards the body, internally rotate the arm, move and hold the scapula down, and when the arms are straight down and stable - it can lift the pelvis - as in crutch walking. The latissimus dorsi also plays a role in helping to expand the rib cage during inhalation (breathing in). It is an interesting muscle because, despite all that it can do, it depends on other muscles to help it out. So even though it is a very important muscle that can do a lot, it is not the sole muscle for any one of its functions. Because of this, the muscle can be in reconstruction or wound repair surgeries.

The lat attaches to the thoracolumbar fascia, so when the lat is tight it can pull the pelvis into an anterior tilt. An anterior pelvic tilt shortens the iliopsoas muscle - which is a hip flexor - when the iliopsoas muscle is tight it can limit hip extension, and lead to gluteus max weakness.

There is a bit of a chicken and egg thing here because weak glutes can cause an anteriorly tilted pelvis which can cause tightness of the iliopsoas and lats. it is the tight or hypertonic iliopsoas that limits the hip extension.

The posterior oblique sling is made up of the lat, thoracolumbar fascia, and the contralateral gluteus maximus. The thought (the research varies on the exact mechanism) is that when the arm moves forward and the contralateral leg moves forward (the reciprocal movement) the lat and glute are stretched - and the fascia is stretched. This increased tension on the muscles and fascia builds up kinetic energy in the tissues. The energy is released as the muscles shorten.

You can kind of feel this if you pull your finger back as far as possible and release it - it bounced back to the neutral position.

The lats run under the arm and internally rotate the upper arm. In a slouched posture the shoulders are forward and the upper arm is internally rotated. Tons of people have tight lats - they get stretched when you extend the arm up overhead, lengthen the spine, and with a posterior pelvic tilt. Many undertrained muscles are tight. There used to be a common belief that tight muscles were strong muscles and weak muscles were losers. This is not true. You can have weak and tight muscles.