So I'm going to demonstrate how to do bicycle crunches for you today.
So you're going to start out lying on your back. You're going to bend your knees at 90 degrees. You can support your head using your hands behind your head. Make sure that you're not yanking on your neck, that's going to cause some neck problems and may cause pain, so just be aware of that. You're just supporting your head.
So what you're going to do is you're going to bring your opposite elbow to your knee, bring it back out to start, and alternate. And you could go about 15 to 20 reps here. I like to use the analogy as if somebody was lifting you up with a string from your sternum. So I don't want to see you doing too much of this, but rather lifting with your whole upper body upward instead of rounding too much. So your elbow to knee, elbow to knee, elbow to knee, just like so. And that's how you do a bicycle crunch.