Plank
Get in push-up position but with your elbows bent and your feet elevated on a bench, chair or couch. Your weight should be resting on your forearms. Contract and tense your ab muscles for 30 seconds, rest for 30 seconds. Repeat twice.
Bench Mountain Climbers
Get in push-up position with your hands on a bench, tense your abs and slowly lift your left knee toward your chest. Pause 2 seconds, lower it slowly, and then raise your right knee. Alternate for 30 seconds, rest for 30, and repeat once.
*For a more advanced version of bench mountain climbers, use a small medicine ball or a small exercise ball to balance your hands on.
Side Plank
Lie on your left side and prop yourself up on your left forearm. Raise your hips until your body is in a straight line from your ankles to shoulders. Tense your abs and hold for 30 seconds. Switch to your right side and repeat. Rest for 30 seconds, and repeat each side once.
*For a more advanced version of the side plank - elevate your feet on a bench or chair.