Once you master the ball bridge, adding knee flexion can further challenge the muscles that support the hip. This exercise is effective at causing co-contraction of the hamstring, hip, and core muscles and is great for hip and core stability.
To perform this exercise, perform the ball bridge and hold the bridge position, then slowly bend your knees and allow the ball to roll toward your buttocks. Be sure to keep your abdominals engaged. Once the knees are bent, hold this position for 2 seconds, then return to the ball bridge position. Repeat the knee flexion 10 times. After 10 repetitions, slowly lower your body down to the resting position.