Start in the sit-up position with your knees bent and feet flat on the floor. Your partner should be in the same position facing you with his feet hooked under your ankles so that your body weights can anchor each other down.
Lie back on the floor and position your hands above your head. This will be your starting position.
Contract your abs to simultaneously rise up, extending your right hand to touch his.
Reverse the motion, coming all the way back down to the starting position, before rising up again, giving a high five to the opposite side.