[DanceDiva]

You're supposed to pick a harder variation.

prone jackknife: None is suggested in the book probably because women usually have to increase upper body strength (which would be the challenge). However, here are 2 variations:

In the harder variation, he uses 1 leg

pike:



crunches: use the harder variations described in the book which go from weighted to long lever to other suggestions.

Also check your form. Here's a good description:


You can also add a pause at the top of the movement to make it harder.