Sit on floor facing partner with knees bent. Hold medicine ball near chest with both hands.
Lie back while holding ball. Raise upper body up by first flexing spine and then flexing hips. While completing sit-up, throw ball to partner. Partner catches ball with both hands and executes same sequence. Continue to exchange ball.
Perform prescribed repetitions or for time. Feet may also be secured under weighted or anchored structure. If feet are not being supported by fixed object, legs may need to be extended somewhat to offer adequate counter balance to upper body.
Exercise intensity is increased by keeping ball closer to chest during sit-up.