Scott Cheatham, PhD, DPT, professor of kinesiology, California State University Dominguez Hills; owner, Sports Medicine Alliance.
Michele Olson, PhD, senior clinical professor of sport science, Huntingdon College, Montgomery, AL.
Walt Thompson, PhD, past president, American College of Sports Medicine.
U.S. Department of Health and Human Services: Physical Activity Guidelines for Americans, 2nd edition.
Exercise is Medicine: Exercising with Osteoporosis.
Mayo Clinic: How fit are you? See how you measure up.
World Fitness Level: How fit are you, really?