FIX:
If you can’t complete at least six reps of hanging leg or knee raises, start by doing reverse crunches to build up your lower-ab strength. This exercise is the same as the hanging leg raise except your body is horizontal, which lessens the resistance. Once you can do three sets of 20 reverse crunches on the floor, move to a decline ab board and do reverse crunches on a 45-degree angle to further increase your lower-ab strength. When you can do three sets of 15–20 reps, you should be able to complete at least 10 reps of the hanging leg raise.