Back in the day ...
I remember back in grade school and high school, situps were always done with the legs straight, knees locked and someone sitting on my ankles. The coach insisted that anything else was a "girl situp" and not for "real men".
He said the samething about the knees on the floor for pushups as well.
He wasn't my favorite person.
But now, pushing 50, I see few people doing crunches with the legs straight although I will see an occasional old-timer doing situps on those boards that elevate with his legs fully extended.
So which is really the best way to do situps for gut reduction and to minimize potential back/neck injury?