As almost anybody who goes to a gym knows, adding resistance to an exercise makes it more effective. For abdominal exercises such as sit-ups, this can be done by using decline boards -- also called slant or incline boards -- and exercise balls -- also called Swiss balls -- in your workout. There are advantages to both. Each activates muscles that might not be engaged by performing the exercises lying on the floor.
Abs Love Gravity
Abs work harder against gravity and a decline board can be adjusted to give you as much as you want. Sit-ups on a decline board are performed with the feet tucked under the braces at the top of the board and your body at a downward slant. Place your hands behind or to the side of your neck. The legs are bent with knees pointing upward to take stress off the lower back. Raise your torso by bending the back and hips until the elbows touch the knees.
The upper back should make contact with the board at the end of the movement. Otherwise, the abdominal muscles may only be partially engaged during the exercise.
Having a Ball
For sit-ups and other abdominal exercises, an exercise ball creates instability by forcing your limbs outside the range of your base of support. Sit-ups done on a ball are something halfway between a crunch and a sit-up because it's difficult to find a position on the ball that allows the torso to come up to perpendicular, or sitting position.
To do sit-ups on a stability ball, first sit on the ball with your feet flat on the floor. Slowly walk your feet forward until the middle of your back is supported by the top of the ball. Your feet should be parallel and shoulder width apart and your knees bent to about 90 degrees. Position your back at the top of the ball at 12 o'clock and your hips at 2 o'clock.
With your hands behind your head, slowly curl your torso toward your thighs. Focus on pulling your rib cage and pelvis closer together. Continue to curl up until your upper back is off the ball. Hold this position briefly while maintaining your balance. Now inhale and gradually uncurl, easing your spine downward toward the ball. If you're having trouble maintaining balance, widen the distance between your feet.
Pros and Cons
So which is better, decline board sit-ups or an exercise ball? It depends on what you're trying to achieve. Doing trunk exercises such as sit-ups on a Swiss ball has been shown to stimulate greater activation of lower abdominal region than the same exercise done on a stable bench. Exercising on unstable equipment such as the exercise ball improves balance and posture.
Decline boards may increase the resistance necessary to build muscles more than doing the same exercise on an exercise ball because the angle requires you to work against gravity. In a study by the American Council of Exercise, decline board curl-ups were shown to activate the external obliques and the rectus abdominus more than supine curl-ups. On the other hand, decline boards won't give you the same full activation of muscle fibers throughout the abdominal muscle group as a Swiss ball.
Full sit-ups should be done with caution because they cause the hip flexors to pull on the lower spine, raising the possibility of injury to the lumbar discs. Be aware that when your torso is raised much past 30 degrees, your help flexors -- and not your abs -- are doing the work. If you do sit-ups with your hands behind your head, avoid neck strain by taking care not to tug on the back of your neck for extra torque.
- University of New Mexico: Superb Abs Guide, by Len Kravitz, PhD
- The Journal of Strength and Conditioning Research: Core Stability Training: Applications to Sports Conditioning Programs
- Ace Fitness: Abs! Abs! Abs!
- ACE Fitness: Should I Train My Abs Every Day?
- ExRx.net: Incline Sit-up
- ACE Fitness: Stability Ball Sit-ups/Crunches