Very little hard data exists related to this question, but an abundance of individual expert opinions. An exception are the measurements from real life situations, which have been measured by Bergmann et. al. via a sensor attached to the implant. Accordingly, daily routine activities had a high impacted on the implant, in comparison to activities which one would have naturally rated as high impact.
Activities which show no or very low impact on the knee do not result in a higher risk for wear and tear. Included here are walking, hiking, cycling, rowing, swimming(crawl), tennis on sand courts, golf, and skiing under good conditions.

Generally, we know that the life of a prosthesis for older patients who have a less active lifestyle is significantly better than for young, athletically active patients. But newer data gives hope and shows that a moderately active lifestyle seems to be a survival rate improving way of loading the implanted joint.