Core-strength exercises strengthen the core muscles. Core muscles include the abdominal muscles, back muscles and the muscles around the pelvis. Strong core muscles make it easier to do many physical activities.

You can do core-strength exercises on a carpeted floor or mat. Breathe freely and deeply during each core-strength exercise. Focus on tightening the deepest abdominal muscle and the one you feel contracting when you cough, also called the transversus abdominis.

Aim to do one set of each exercise for 12 to 15 repetitions. If you have back problems, osteoporosis or other health concerns, talk to your health care professional before doing these core-strength exercises.

Abdominal crunches are a classic core-strength exercise. To do an abdominal crunch:

• Lie on your back and place your feet on a wall so that your knees and hips are bent at 90-degree angles. Tighten the abdominal muscles.
• Raise your head and shoulders off the floor. To avoid straining your neck, cross your arms on your chest rather than locking them behind your head. Hold for three deep breaths.
• Return to the start position and repeat.

To improve core strength of many muscles at one time, try a bridge, sometimes called a back bridge or a glute bridge:

• Lie on your back with your knees bent (top photo). Keep your back in a neutral position, not arched and not pressed into the floor. Try not to tilt your hips. Tighten the abdominal muscles.
• Raise your hips off the floor until your hips line up with your knees and shoulders (bottom photo). Hold for three deep breaths.
• Return to the start position and repeat.

The single-leg abdominal press is another popular core-strength exercise. To do this exercise:

• Lie on your back with your knees bent (top illustration). Keep your back in a neutral position, not arched and not pressed into the floor. Avoid tilting your hips. Tighten the abdominal muscles.
• Raise your right leg off the floor so that your knee and hip are bent at 90-degree angles. Rest your right hand on top of your right knee (bottom illustration).
• Push your hand against your knee while using the abdominal muscles to push your knee toward your hand. Keep your arm straight. Hold for three deep breaths.
• Return to the start position and repeat using your left hand and left knee.

To improve your core strength more completely, try variations of the single-leg abdominal press:

• Opposite hand on opposite knee. Push your right hand against your left knee while pulling your knee toward your hand (top illustration). You'll be pushing and pulling across the center of your body. Hold for three deep breaths. Then do the exercise using your other hand and leg.
• Hand on outside of knee. Place your left hand along the side of your left knee (bottom illustration). Use your hand to push your leg inward. At the same time, create resistance by pushing your knee away from the center. Hold for three deep breaths. Then do the exercise using your other hand and leg.

When you're comfortable with the single-leg abdominal press, try the double-leg abdominal press for more core strength:

• Lie on your back with your knees bent (top illustration). Keep your back in a neutral position, not arched and not pressed into the floor. Avoid tilting your hips. Tighten the abdominal muscles.
• Raise your legs off the floor, one at a time, so that your knees and hips are bent at 90-degree angles. Rest your hands on top of your knees (bottom illustration).
• Push your hands against your knees while using the abdominal muscles to pull your knees toward your hands. Keep your arms straight. Hold for three deep breaths.
• Return to the start position and repeat.

These variations of the double-leg abdominal press also build your core strength:

• Opposite hands on opposite knees. Place each hand on your opposite knee, toward the inside of your knee (top illustration). Your arms will cross over each other. Push your hands against your knees while pulling your knees toward your hands. Hold for three deep breaths. Repeat.
• Hands on outside of knees. Place your hands along the sides of your knees (bottom illustration). Use your hands to push your knees inward. At the same time, create resistance by pushing your knees away from the center. Hold for three deep breaths. Repeat.

This core-strength exercise is called the quadruped and sometimes called the bird dog:

• Start on your hands and knees. Place your hands directly below your shoulders, and line up your head and neck with your back. Tighten the abdominal muscles.
• Raise your right arm off the floor and reach ahead. Hold for three deep breaths. Lower your right arm and repeat with your left arm.
• Raise your right leg off the floor. Tighten the trunk muscles for balance. Hold for three deep breaths. Lower your right leg and repeat with your left leg.
• For added challenge, raise your left arm and your right leg at the same time. Repeat with your right arm and left leg.

Another good core-strength exercise is called the modified plank. In a plank, you raise yourself up on your forearms and feet while keeping your body lined up with your hips. To do a modified plank:

• Lie on your stomach. Raise yourself up so that you're resting on your forearms and knees. Line up your head and neck with your back. Place your shoulders directly above your elbows. Tighten the abdominal muscles.
• Create resistance by pressing your elbows and knees toward one another. Neither should move from their positions on the floor. Hold for three deep breaths.
• Return to the start position and repeat.

For more core-strength exercises, try these variations on the modified plank:

• Lie on your stomach. Raise yourself up so that you're resting on your forearms and knees. Line up your head and neck with your back, and place your shoulders directly above your elbows. Tighten the abdominal muscles.
• Raise your right arm off the floor (top illustration). Hold for three deep breaths. Repeat with your left arm.
• Raise your right leg off the floor (bottom illustration). Hold for three deep breaths. Repeat with your left leg.
• For added challenge, raise your left arm and right leg at the same time. Repeat with your right arm and left leg.

The side plank challenges your stability and improves core strength by working the muscles along the side of your body:

• Lie on your left side, raising yourself onto your left forearm (top illustration). Place your left shoulder directly above your left elbow, keeping your shoulders, hips and knees in a straight line. Rest your right arm along the side of your body.
• Tighten the abdominal muscles. Hold for three deep breaths. Repeat on your right side.
• For added challenge, balance on your left hand. Raise your hips off the floor and extend your right hand toward the ceiling (bottom illustration). Hold for three deep breaths. Repeat on your right side.

The superman is another core-strength exercise that can help strengthen your lower back:

• Lie on your stomach with a rolled towel or a small pillow under your hips to support your back. You also might use a folded towel to support your head. Tighten the abdominal muscles.
• Raise your right arm off the floor (top illustration). Hold for three deep breaths. Lower your right arm and repeat with your left arm.
• Raise your right leg off the floor (bottom illustration). Hold for three deep breaths. Lower your right leg and repeat with your left leg.