This exercise comes from Al MacIsaac, who worked out at the same gym that I do when he was in town last season as the Rockford IceHogs’ general manager. It takes a little practice, but it puts a lot of muscle groups to work.
You need a flat bench and a medicine ball that you can handle. A ball between two and eight pounds will work.
Hold the ball in either hand and lean back at one end of the bench as if you were going to perform V-situps. When you are stable, flutter-kick your legs up and down as you toss the ball back and forth between them. You can do it if you start slowly and gradually pick up speed as you get better at it.
MacIsaac did it several times during his workouts in between other lifting. When I remember to do it, I usually try to do three sets for as long as I can.
One warning would be that, because of the spinal flexion and the extended legs during the exercise, I wouldn’t recommend it for anyone with low back issues or post menopausal women.