A study presented by Cliff Colwell, M.D. at the knee society, during the 75th annual American Academy of Orthopaedic Surgeons meeting in San Francisco, California in March 2008, demonstrated the forces across a knee replacement following surgery. Using an instrumented knee prosthesis, that measured knee forces, it was found that biking placed 1 times body weight across the knee, use of the Stairmaster is 2 times body weight, jogging 4 times body weight, rowing on an ERG machine 0.5 times body weight, and lunging is 2.5 times body weight. This insightful study gives some objective data to the forces placed on a knee replacement following surgery. Wear in a knee replacement is affected by patients activity, the patients weight, and surgical technique. Knowing the stresses placed across the knee replacement can help better educate the physician and the patient as to the appropriate activity level following surgery.