The second rite bad for your back? Not to dismiss your friend's physical education, but they are basically leg lifts...
I have shared these exercises with my chiropractor, and he did not mention anything about any of these exercises being bad for my back. Instead he encouraged me to continue with the exercises. At this point my back feels better than ever...
And when I do them, I feel the pain in my stomach, more than my back. Are you bracing yourself with your hands at your sides as the rite describes?
I started slowly, and now do all 21 repetitions for each rite...and when I have a day that starts without them I feel sluggish...