Classic sit ups not bio-mechanicly relevent?

Video of a couple of my players performing the ground based abdominal work and med ball rebounds in real time; 1 series each.

They go at their own pace in terms of rest interval between movements and reps average 40-50 per move with a couple exceptions in which the movement is performed for half the reps on one side then half on the other.

http://sharing.theflip.com/session/66330892f0f11bd24fffdce884052aea/video/12257862