What is proper form for kneeling cable crunches?

Question

What is the proper form for doing kneeling cable crunches? Specifically, I am curious about the following:

1. Should you face the machine, face away from the machine, or are both okay?
2. How should you position your arms throughout the exercise? For example, should they stay extended the whole way down like you are bowing to someone?
3. How should you position your upper body throughout the exercise? For example, do you treat it like a crunch where you start straight and then curl into your chest?
4. What angle should you be starting at? 90, 67.5, 45?
5. Is there anything else I missed out on that I should be conscious of during the exercise?

Answer 1

I never performed that specific exercise, but it is listed on ExRx's database here, with alternative technique here. Generally, I trust that website (it is recommended by the ACSM, so it's not just your average website).

To answer your specific points:

1) Both can be used but I'd say that facing the machine is better. It probably makes the resistance direction (which is near vertical if you face the machine, as in the first link) closer to the movement direction.

2) Assuming that you use this exercise to isolate your abs, you should put your arms in a position which is as favorable as possible, which in this case means bending them and placing your hands on top of your head (see the link above) if you are grabbing a bar, or on the side of your head if you are using stirrups. Extending your arms will work your shoulder and arm muscles isometrically if you keep your arms rigid; if you don't keep them absolutely rigid, your arms will help your abs, defeating the point of the exercise.

3) Yes, you should treat it like a crunch. As that link says, "movement occurs in waist, not hips". Your torso should bend throughout the exercise. The most important distinction is to ensure that you are bending your spine: think of bringing your upper chest to your groin. You should NOT bend at the hips, as you would in a bowing movement.

4) This will somewhat depend of your body proportions but the first link I gave uses something like 67.5.

5) That link has a few more pointers, but I think the major points were covered here.

Answer 2

1) You should face the machine. Facing away can work but it forces you into some bad posturing.

2) You should find a place for your arms to stay. If you prefer arms straight you should let your biceps an lats be relaxed. It is very easy to use the muscles in your arm without realizing it. If bent is more comfortable, once you get in the right position, you should lock everything from your chest up in place. This will ensure that you don't try to pull down with any other muscles.

3) Your body should be straight from shoulders through your waist to your knees. When you perform the crunch think of moving the ribs right below your pecs into your belly button. Exhale while you crunch. This will help you engage your abdomen as well.

4) This depends on your level of strength with your core. If leaning at even an 80º angle makes you sway your back or pooch out your butt it is too far. The further your knees are from the machine the harder it will be. This is because not only working your abs this way, you are also having to use all of your stabilizer muscles to keep from falling forward.

5) Try to be conscious of yourself and not others. Everyone is different and starts at varying levels. Just do your best with the best form possible and you will be okay!