Ouch !!!

I'm no expert on exercise but I know that you are to bend your knees and keep your feet flat on the floor so you don't arch your back . Other wise you will likely feel pain. Good Luck

Don't attach your feet to anything, and only crunch far enough to just get the small of your back off the ground/whatever you work on or not even that far.

You are supposed to arch your back (not hyperextend but the other way). You don't need no weight until you can do at least 25 without any.

If no one is holding your feet, then keep your calve/shins parallel to the floor. .(Feet off the ground) Pretend you have an orange tucked under chin (or put a tennis ball there) raise your shoulder blades off the floor, then go back down. DO NOT PUT YOUR HANDS BEHIND YOUR HEAD!!! This will tempt you to pull on your head to force another crunch and you will injure yourself. Either put them to the side of your head, pinch your earlobes, or cross them across your chest. Regardless, when you go up, touch your elbows to your thighs. This will keep you from going too high. If your lower back hurts when you do crunches, lose the weight. Do more reps with the less weight.