Your core is your center and is considered the powerhouse of the body. It consists of all your torso muscles from your upper back to your pelvis. To keep it strong, do this simple yet challenging exercise to tighten your abs and strengthen your back and hip muscles. Be sure you only twist from your waist up. Your lower body should remain stationary throughout the exercise.

1 Hold a 5- to 8-pound dumbbell with both hands and sit on the floor with your knees bent and your feet flat on the floor. Inhale and, on the exhale, tighten your abs, pressing your navel to your spine. Lean back slightly and extend your arms in front of your chest.

2 Slowly rotate your arms and upper torso to the right. Keep the dumbbell in front of your chest. Hold for three seconds, then rotate back to the center. Do three sets, rest for 10 seconds, and repeat on the other side.

This article originally appeared in the Los Angeles Times in the "Good Form" feature of the Health Section. "Good Form" is updated with a new Karen Voight article each Monday.