Kneel on your hands and knees. Make sure your hands are right under your shoulders and your knees are right under your hips. Now tighten your tummy muscles and tuck your tail, arching your back up like an angry cat (see left photo below). Hold this position briefly, about 3-5 seconds. Then drop your back down and stick your buttocks up, like an old cow (see right photo). You shouldn't feel any discomfort in either direction, if you do - BACK OFF! Don't go quite so far in the motions. Repeat this cycle, arching and then sagging, about 10 times or as directed in the instructions from your coach.Key Points• The movement should come from your back, don't let your elbows flex and extend• All movements should feel comfortable, you should never feel pain in your back or legs• Cycle through the positions slowly and gently, no need to hold for more than a few seconds in any position.