Lifting one foot turns the bridge into a one-sided hip extension. The hips should stay level. If they twist, the load is too ambitious.

Diagrams show the shape of the movement. Follow the written steps before you add load.
Equipment. Bodyweight, Mat
Muscles. gluteus maximus. Also hamstrings, core, gluteus medius
All Cheeked Up publishes general fitness education. It is not medical advice, physical therapy, or a promise that your body will change. Stop any exercise that causes pain and talk with a qualified professional about injuries, pregnancy, or health conditions before you train.