WSP - Phase 2

Hi yall!
I’m on the second phase of the WSP and so far it’s going great. I have a question about day 1. I looked the forum and didn’t find the answer so I’m bugging you…(-:

How can I do 4 reps of Swiss ball crunches on a 6 RM?
i.e., how can I make the crunched more challenging?

Also, my knee really hurts from sprinting. Does elliptical HIIT can be considered a good replacement?

10X!!

b.

Grab a plate, or plates, hold them outwards from your chest as your do the crunch.

Oh yeah, I prefer doing HIIT on the eliptical, I find no need to mess with the difficulty settings then, you control how hard you want to go. Enjoy.

Thanx!!