The knee raise on parallel bars is without doubt one of the best core exercises you can do. Unlike laying ab exercises that usually target few muscles, This exercise targets the entire abdominal region with an emphasis on the hip flexors as the primary mover and the lower abdominals.
Besides training your abs, knee raises help to strengthen other muscle groups such as your arms, back, shoulders, triceps and even your legs, and it will also improve your grip strength.
One of the most amazing benefits of this exercise is that it trains all of the muscles that support your spine while simultaneously unloading and decompressing your spine.
Bar ab exercises might be more suitable for people with lower back problems, since they tend to cause less strain on the back than laying ab exercises when done correctly.
Before you are ready to attempt a parallel bars knee raise, you’ll need to have the strength to hold on a parallel bars for at least 20 consecutive seconds. If you can’t do that yet, practice holding up for as long as you can. It shouldn’t take too long to build the endurance needed to begin.
Pull your shoulders back and down don't let your body to fall down in a way that your shoulders will be close to your ears. This helps protect your shoulders from injuries.
It is very important not to use momentum on this exercise, Make sure to move your legs slowly, swinging your legs and torso will make your workout much less effective.
Make sure the movement occurs in your hips and not in your lower back.
Using a parallel bars with a back pad like on a Captain's Chair will help you to maintain a proper position and avoid swinging your back to do the lifting.