Ab Crunch Machine

I am a tall (5'10), overweight woman who has been trying my luck at the local gym. There is a machine that is for your abs that is supposed to simulate a crunch.

You sit in it, place your arms on the bars above you and your feet underneath the pads so you pull down with your arms and push up with your feet at the same time. There is an option of putting weights on this machine so not only do you do your own body weight, you can add more.

For someone like me, this is a nightmare. I have asked the gym trainers to assist me because I must be doing something wrong in how I position myself in it. I can barely get my legs under the bar without feeling like I am falling of the machine. I think I am simply too tall and my calves are too thick for this machine. But I think most people struggle with it.