The hanging leg raise is commonly mistaken as primarily a lower abdominal exercise, probably due to the fatigue noticed in the hip flexor muscles by athletes. During the initial portion of the exercise, as the thighs are brought up to parallel with the ground, the hip flexors are highly active. As the thighs go past parallel, and the athlete begins to flex his/her pelvis towards their ribcage, the abdominals are strongly recruited, with the hip flexors taking a backseat.
The easiest way to perform the leg raise is with the legs bent, but the exercise can be made harder by keeping the legs extended throughout the raise. Another twist on the exercise is to drastically reduce the range of motion, turning it into a hanging hip raise. This entails not letting your thighs go below parallel to the ground, therefore cutting out the initial leg raise portion of the exercise where the hip flexors are the primary recruiter. This places greater tension on the abdominals.