2, lateral lunge: If the waist is too bent, it will cause a load on the spine. The correct way is to keep your back flat, don't lift your pelvis, and make sure your knees bend 90 degrees when you squat.
3, flat support: If your back is not straight enough when doing flat support, then this exercise will lose its effect. The correct way is to keep your body in a straight line from head to toe and your arms at 90 degrees. Don't crookneck.