Whether you're hanging from a pull-up bar, have your elbows in ab straps, or you're on a machine, hanging leg raises are great for ab development... if you do them right. But most people don't. They start with their legs hanging straight down then flex at their hips. That's mostly a hip flexor exercise, not an ab exercise.Hanging Leg Raises Done the Right Way
Hang from a pull-up bar with an overhand grip and your hands roughly shoulder-width apart. Flex your hips and bend your knees, holding them above your hips in front of your torso.
In a controlled fashion, roll your torso upward, bringing your knees toward your chin. Slowly reverse this motion without allowing your knees to become un-tucked from your body. Don't use momentum or jerk your body at any point.
Here's how hanging leg raises look in a "captain's chair" machine:
The way hanging leg raises are usually done – with your legs hanging down and flexing at your hips – is primarily a hip flexion exercise. Although this certainly involves the abs, the degree of involvement is negligible. Tuck your pelvis and you'll target the abs better.