While I was teaching and demonstrating bodywaves in my ATS class last week, one of my students asked me, "Are you doing a bellyroll?" and my answer was "Yes, sort of."
In a bodywave, the ribcage shifts forward and lifts, then the back body rolls back against an imaginary wall, with the shoulders touching first, then the ribcage, lower back, and finally the hips.
So, muscularly speaking, the latissimus dorsi contract to send the chest up and forward. Then, to bring the chest back, the rectus abdominis contract, first the upper section, then rolling down to the lower section. Finally, the contraction in the lower abs release, taking the spine back to the original dance posture.
In a bellyroll, the lats are out of the equation and the spine is held in dance posture. The rectus abdominis is still working, however, it's the obliques (mostly external, I think) that are driving the movement and the rectus abdominis is going for a ride on top.
Or at least that's how it's happening in my body.
Anyway, in my first go round at ATS General Skills, I learned about the latissimus dorsi driving the movement in Egyptian Basic. Try generating that movement ONLY using your lats. Amazing! You'll see in the attached image that the point of origin of the lats are way down towards the base of the spine, which gives the Egyptian Basic that dramatic swivel. In barrel turns, the lats are working to compress the side body for the initial "scoop" part of the turn. As mentioned above, in bodywaves, the lats are drawing together lifting the ribcage forward and up. I was under the misconception previously that the rhomboids were the inital part of the bodywave. While this will shift your shoulders back, your chest will not move up at all. You need to contract much lower down your back, towards the bottom tips of the shoulderblades to get that lift. So yay for the latissimus dorsi! To access your lats, transition between upward dog and downward dog. Down-dog lengthens the the latissimus dorsi, and upward dog works them.
It's very helpful for me to figure out exactly what muscle is working and how, both in yoga in dance, and I find descriptions like "this is a skeletal movement" to be frustrating and problematic. Bone doesn't move on it's own, so there must be some muscle taking that bone from point A to point B. You don't have to be an anatomy expert to investigate your movements and see how your body works.
If you've made a discovery of your own, please share! Also please let me know if my analysis make sense at all!