This exercise is a great way to train your core muscles, but it's also a challenging shoulder-stabilization move. If you have weak shoulders, however, stick with the standard plank position and don't attempt to rotate into side plank position until you develop adequate shoulder strength.
Begin on all fours. Position your hands directly below your shoulders. Place your feet shoulder-width apart and straighten your legs, balancing on your hands and toes. Use your core muscles to lift and support the weight of your pelvis so you don't sag in the center. Focus on forming a straight line with your body. Hold this position for three full breaths. Bend your knees, rest for a few seconds and repeat, or continue to the more advanced position.
Keeping your body in a straight line, shift your weight to your right arm and rotate your entire body to the left by pivoting on the edges of your feet. Raise your left hand directly above your left shoulder. Keep your right shoulder pressed down away from your right ear. Hold this position for a few breaths. Return to forward plank by pivoting back to your toes. Repeat on the other side.
Voight is the creator of a line of fitness DVDs, including "Sleek Essentials."