Sitting posture: point your toes to the ground, raise your heels as high as possible, and the triceps of your calf are extremely tight. Hold this position for 8 ~ 10 seconds or a little longer, and then relax.
Lie on your back, the lower limbs and upper body are tilted into a V shape at the same time, and the rectus abdominis is extremely tight. Keep this static posture for 8 ~ 10 seconds or a little longer, and then relax. You can try. It's quite effective