1. Begin on your hands and knees.

2. Keeping your back straight, lift the right arm and left leg until they're level with your body. Hold your balance and keep your torso tight.

3. Lower back down and repeat with the left arm and right leg. Repeat for two sets of 12 repetitions, alternating sides (one repetition includes both right and left sides).

1. Begin in pushup position, then place your forearms on the floor and press up into a flat-back position on the toes.

2. Keep your hips down so the body is in a straight line from head to heels.

3. Hold for 30 to 60 seconds, lower and repeat. To modify, lower one or both knees to the floor.

1. Starting on your knees, place your forearms on an exercise ball and roll forward a bit until your back is flat.

2. Straighten your knees and bring your body into a plank position.

3. Hold for one to two seconds, lower your knees and repeat for 10 to 12 repetitions.

1. Get into plank position with feet/shins resting on the ball, hands under shoulders and abdominals contracted.

2. Keeping the core tight, lift your right leg off the ball a few inches and then lower it.

3. Lift your left leg off the ball and lower it back down. Continue alternating legs for eight to 10 repetitions on each side.

1. Lie on your side balanced on your forearm or leaning on your hand, with your feet and hips stacked on top of each other.

2. Holding your torso steady, slowly contract abdominals and lift your hips off the floor (don't sink into the shoulder).

3. Lower and repeat on the other side. To modify, keep your knees bent, or position your feet wider rather than stacked. Do two sets of 10 repetitions on each side.