Lie flat on a roll-up chair or bed, with your thighs vertical, your calves horizontal, and your hips slightly suspended. Then tighten the abdomen so that the back leaves the bed surface as much as possible, but most people should only leave a little, about 30 degrees. Hold it hard for a few seconds and lie flat. Then repeat this action immediately. Repeat to exhaustion, for the first group. Rest for 30~90 seconds, and then continue to repeat until exhaustion, which is the second group. Just do more than four groups. Rest for 48 ~72 hours before the next abdominal muscle training, so as not to cause fatigue and dullness.