It's true that heat can build up inside a joint replacement from friction during activity. It doesn't always go away fast enough. The temperature goes up with use. Half the increase occurs during the first five to six minutes of exercise (walking or biking). The maximum temperature occurs after the first hour.
Blood supply to the joint helps cool any temperature increases. The patient's size, activity level, and type of training affect temperature. Synovial fluid in the joint helps transfer the heat to nearby tissues.
Right now there are more unknowns than knowns about this problem. For example doctors don't know if age makes a difference. It seems like younger (more active) patients would have greater temperature increases. Studies haven't proven this yet.
Activity and exercise are important though. So until doctors have an answer to this question, it's best to keep a consistent level of activity and exercise. Keep your regular follow-up appointments with the surgeon to check your implant each year, too.