American Physical Therapy Association
http://apta.org

American College of Sports Medicine
http://acsm.org

American Medical Association
http://ama-assn.org

National Institute on Aging
http://nia.nih.gov

MEDLINEplus
http://www.nlm.nih.gov/medlineplus

Centers of Medicare & Medicaid Services
http://cms.gov

Web MD
http://webmd.com

American Senior Fitness Association
http://seniorfitness.net