The latissimus dorsi, the lats, are the only muscle that connects the arm to the spine and pelvis and they play an important role in backbending in yoga. Backbends should feel good and too many people are suffering when backbending which should lengthen and extend, rather than compress, the spine.
The ability to extend the spine involves the successful activation of many muscles. Three in particular include my favorite muscle the psoas, the rectus abdominus (the sit ups muscle) and the latissimus dorsi. If these three muscles turn on in wheel pose the back of the body will lengthen as the front of the body shortens.
We tend to be splayed open in the front of the body and short and tight in the back. I think everybody leans backwards in tadasana and compresses their lower spine and this leaning backwards manifests in our backbends.
I wrote about the knees in backbending and how the knees need to align over the ankles in order to gain access to the psoas and the core. If we want the upper body and lower body to work in concert we have align the elbows and wrists in a similar way to the knees and ankles.
The elbows have a tendency to move wide of the wrists as the body rises into wheel pose. This takes the latissimus dorsi out of the game and makes getting extension at the back of the body much harder.  You can’t put too much effort into moving the elbows in toward the midline.
- When the psoas can do its thing, drawing the lumbar vertebrae forward and down, with the help of the inner thighs,
- and the rectus abominus closes the gap between the pelvis and the rib cage,
- the environment is created for the latissimus dorsi to engage as the elbows move toward the midline and the forearms try to move parallel to eachother.
When all of that happens the deep muscles of the spine can all tone and extend as designed. The body is a machine meant to work very specifically. When we use it as such everything get easier.
Here is a little anatomy addendum…
The body has many different ways of increasing force within the machine. The patella or kneecap is embedded into the quadriceps muscle in order to increase the power of that muscle. The rectus abdominus has tendons inserted between the muscles that make up the six pack in order to increase the strength of such a long muscle. The latissimus dorsi is twisted in its insertion onto the arm and it straightens when it extends. This is how you increasing the force generated by the latissimus dorsi if you do your wheel pose correctly.