The hanging crunch works the hip flexors more than the ab muscles.
Hanging crunches involve tucking your knees up to your ribs from a straight-leg position while hanging on a bar, a pair of Olympic rings or a similar apparatus. As you do so, you keep your torso stationary and minimize curving your lower spine. You can also perform this exercise with your legs straight. Although you might feel this exercise strengthens your outer abdominal muscles, it actually works more on deep abdominal and spine stabilization and strengthens your hip flexors.
Abdominal Function
Your abdominal muscles are made up of two layers, which are the inner and outer units that make up the main part of your core. The inner unit consists of muscles that are closest to your spine and organs, and they keep your body in alignment to avoid injury and to provide a source of strength. The outer unit, which consists of muscles near the surface of your body, moves your body in different directions. Both units work together with other muscles in your back, hip and legs to produce and reduce force and to keep your body in balance and stability while moving, according to the National Academy of Sports Medicine. With proper form, hanging crunches can strengthen your core.
Form
This exercise requires you to maintain a neutral spine posture where your spine retains its natural S-curve throughout. This automatically engages your inner unit muscles to stabilize your spine while you move your legs up. To do this exercise, hang from a bar or Olympic rings with your arms about shoulder width apart and your legs straight below your body and off the ground. Lift your knees up to your ribs and hold this position for one second. Do not jerk your legs up. Lower your legs down without moving your spine.
Contraindications
Do not perform this exercise if you have a weak core and have lower back and hip pain. Because this exercise works mainly the hip flexors, which are attached from your lower spine to the front of your pelvis, tight hip flexors place excessive stress on the lower spine by pulling it forward, explains physical therapist Gray Cook, author of "Movement." This reduces your stabilization strength in your core muscles.
Misconceptions
Abdominal exercises, including this one, do not reduce body fat from your midsection because the duration and intensity of the exercise is not long enough to elicit fat metabolism. Fat loss occurs when you expend more calories than you consume. Focus on performing full-body exercises, such as kettlebell training or sprinting, and adopt a healthier diet to achieve long-term fat-loss goals, says Juan Carlos Santana, director of the Institute of Human Performance.
