I completed both of those challenges two weeks ago. I've been a big fan of the website for over a year now. I used to on and off do the program... Like I said, I started it the last time about 8 weeks ago and finished it up two weeks ago. I also did my own version for a pull up challenge. Steve is going to post up one but he hasn't had time yet.
During the rest period of one, do the exercise for the other.
In other words, when you just did your first situp rep, flop around and knock out the pushup reps. It's a great endurance twist on an already kickass routine. You may need to take the prescribed break somewhere, but it'll work ya like crazy.
