At a recent meeting of the American Association of Hip and Knee Surgeons in Dallas, Texas (November 3-4, 2007), a symposium on activity after joint replacement was convened. Several factors influence the function of joint replacement. These include trends that show the average age of the patient undergoing joint replacement has decreased over the last two decades. The life expectancy of these patients is therefore increasing. Body weight has increased over the last two decades with the majority of patients undergoing joint replacement, overweight or obese. During that time period implants have improved, fixation has become reliable and most likely long-term, but the weak link in the system is the bearing surface. Over time, bearings surfaces will wear and the modular junctions that attach the bearing to the joint can break down over time. All of these factors influence the durability of the joint replacement. Typically, walking places three times body weight across the joint, jogging is six times the body weight, and skiing nine times the body weight. All of these activities depend on the duration of the activity, the intensity, and how frequently the patient engages in these activities. While we can not absolutely prescribe the activity level of our patients, we do recommend using common sense in trying to balance quality of life with desire for long-term function of your joint replacement.