Hi there,
The general rule of advice should be to ask your surgeon as, depending on the type of implant you have in the knee, there maybe certain restrictions on your activities.
That said, as a general rule, it is probably best to avoid/limit high impact activities such as distance running or contact sports. for most people, non-impact sports, gym-based and light aerobic activities will be best. Swimming is an excellent way of keeping fit without over-stressing the knees, as is cycling and cross training.
It is also VERY important that you take part in your post-op rehabilitation and recovery. In doing so you will optimise your post operative outcomes and also the lifespan of the prosthesis.
Hope this helps
BW
Dr Dinesh