Between two hacking sessions I also did a yoga session today. I think that I realized, why such simple actions take such great effort when you are doing proper yoga. I think that the point is that you twist/bend/compress you body into an inconvenient position and then the real exercise starts: 1. maintaining a position is harder then assuming it, 2. you must breathe deeply and forcefully thus forceing your lungs to press against other organs and expand you body. Your muscles will have to strain quite a lot just to keep your position under increased pressure. Then when you breath out, your muscles will relax. This is just like your common workout in the gym, but in the case of yoga you will strain such muscles that you would not be able to strain otherwise.
Note: I somehow feel that my spellcheck is not working. That sucks :P