First do belly roll, lie flat and close together, lift your legs, bend your knees slightly, put your hands next to your ears, bend your arms and clamp your elbows, then roll up your upper body by the strength of your abdominal muscles, and then restore. Pay attention to return your shoulders to a horizontal position every time, and don't touch your knees. The point is to roll up your abdomen.

Then lie on your back and lift your legs. When you put your legs down, relax like a free fall? When you reach the level, your abdomen stays still. Buffer? Keep it level and lift it slowly.

Why don't you do an aerobic warm-up before you come back? For example, jog for twenty or thirty minutes and do it in groups. Each group should be exhausted, rest for no more than two minutes, and then continue. Abdominal muscle training is not heavy, but it works many times.