I like this one because it can be done between sets on other machines.
Find a bench with enough room on both sides.
*Sit in the middle of it.
*Lean back 45 degrees.
*Help balance with hands - hold the edge of the bench that's behind you.
*Lift both legs with knees slightly bent. Lower part of the legs should be parallel to the floor at the top of the lift.
*Straighten the legs as you lower them to be parallel to the floor at the bench level only (not lower).
*Do 20 reps.
*Lower legs to the floor, rest, do a set on another machine (arms for example), repeat the ab crunch 2 more times.
It's a nice fill-in, allows your arms (or whatever you're working) to cool off between the reps, and you use the time to your advantage.
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