For some students cactus at the wall is a very intense experience. I stopped teaching it in classes because of how strong it can be. While I use it I find the more gentle, Cactus on the Back, to be a more effective shape. But doing it at the wall is an eye opener simply to see how tight your latissimus dorsi can be.
I thought I should explain how the tight latissimus dorsi manifests. If the lats are long and loose when you stand against the wall, everything can release backwards. The rib cage can be against the wall as well as the upper back, head, arms, wrists, and fingers. The long lats let everything connect to the wall.
If the lats are tight one thing that might happen is the base of the rib cage will be pulled off of the wall. Another issue is in the arms and wrists. If the wrist can’t touch the wall or if the five fingers of each hand can’t open for the fingernails to touch the wall, it is the tight latissimus dorsi pulling everything away from the wall.
You can play with the opposite ends of the shape. If you put the back solidly against the wall the wrists will likely pop off and vice versa. Interestingly, it is not always so great to be able to release everything against the wall because this, as in my case, often represents lats that are too long and loose, and lack needed tensile strength.
The attempt to open these body parts to be able to touch the wall is an attempt to stretch the latissimus dorsi.