WOOO: you only doing Hatha Yoga, including Pranic practice? Might find Ayurvedic of interest. Been involved, on and off, since a teenagers. Interesting stuff. Where I have gone for Hatha, everyone wears white loose Hindu style clothes. The mind is on the pain reflex of some of the position holds, not letting the mind wander to other more delights..like some amazing women (MILF's mostly). As we know, certain breathing meditations increase the sexual power to a much higher degree. (any time, any where)
Galeniko is completely correct, about not having isolation of a specific muscle (as the delt structure was noted). The body acts as a total unit; action (cause) and counter action (effect). Even when you think your doing strict, isolation curls, the triceps are still brought into he action. If injecting a muscle numbing agent into the heads of the triceps, doing a simple curl may prove to be a difficult task.
Any overhead pressing recruits all three heads of the delts, as well as the traps strongly. Any form of arm raises (front, side, rear) also requires all three delt heads. Raising the hand above shoulder level, calls upon the traps to give aid. Good Luck