I just thought of adding a small tip for everyone's benefit here -- last year, I was motivated to exercise in order to lose weight and I did a short warm-up session consisting of stomach vacuum, stomach crunch, some stretches and then jogged up and down the stairs within my home - I jogged 4 sets of going up and down 8 steps. This made me lose 8 lbs in 2 weeks. I just had to stop because shortly later I was diagnosed with OsteoArthritis of the left knee. If not, I would have continued with this wonderful exercise. I hope some of you who can do this exercise will do it and benefit from it!