The seated alternating reverse crunch increases strength throughout the core and lower back. The exercise also improves balance and coordination.
Sit on the floor with your arms straight down by your side, palms pressed into the floor. Begin by bending one knee so that your foot is flat on the ground while straightening your other leg completely, elevating it off the floor by an inch.
Tighten your abs and rock back onto your shoulder blades and while bending both knees. Legs should come over your head from the momentum of the roll. Press your hands into the floor behind you for support.
Rock forward to the starting position, returning to the original leg position with one leg bent and the other fully extended. Use both your abs and arms to lift your hips slightly off the ground. Then return to the starting position.
Keep your feet off the ground for as much of the rolling motion as possible.
Keep your back flat during the exercise to avoid injury.