Alternating Lying Leg Raise
The alternating lying leg raise is a simple hip flexor and pelvic stability exercise.
Lie on your back, hold the abs in a crunched position (keep pelvis rotated posteriorly) and raise one straight leg to a vertical position while the other remains just off the floor, then alternate while maintaining the same pelvis position.
The alternating lying leg raise is a more accessible variation of more intense hip flexor exercises like the hanging leg raise, and like the dead bug, the purpose is to both strengthen the hip flexors independently for balance, and the ability to stabilize the pelvis against unwanted movement.
3-4 sets of 10-50 reps or doing max reps in set periods of time such as 20-60 seconds are good prescriptions.