Having excellent hip flexion means being able to abduct, adduct, extend, and rotate the hips freely with ease and great range of motion, especially with a weight under your back.  If you have tight hip flexors, anterior pelvic tilt, and/or can't squat below parallel, you will need to work on your hip flexor mobility.  Here's some effective way to do just that. Hip flexion is the technical term for a decrease in joint angle between the femur and pelvis. This occurs from either side of the joint, by raising the leg...