If you run regulary, is it inevitable that you will bugger up your knees eventually? Is there anything you can do to stop this happening?
Max Walker, London

The chances of this happening to the average punter are pretty slim. Very few studies are available for lifelong athletes, and most come from Scandinavia, where high-level physical activity continues until very late in life. Essentially, these show that moderate amounts of running do not cause osteoarthritis in the lower limb. Another study showed that runners reported knee osteoarthritis and knee pain more often than non-runners, whereas the occurrence of hip osteoarthritis and hip pain did not differ. However, if one runs on hips and knees which have been injured in the past, or if one has markedly bow legs or knock knees, then the chances of shortening the shelf life of the knees increase. Some people advocate insoles to absorb the impact of running, but this is not proven.

The good news is that for people with a long-term endurance training background, the risk both of heart attacks and lower-limb disability is low. Therefore, if you have not been injured and you enjoy running, keep on going. Use at least two different brands of good running shoes to alternate every third run (it might sound like an unnecessary cost, but remember that an hour with an orthopaedic surgeon will set you back £150).

If you have had an injury, consider switching to a non-weight-bearing endurance activity such as swimming, rowing, going on the cross trainer, or on the Stair Master. Actually, just to be on the safe side, why don't you rotate between all these activities? You may end up becoming a multi-sport athlete.

· Professor Maffulli is a consultant orthopaedic and sports injury surgeon at Keele University medical school. If you would like to ask him a question, email fitness@theguardian.com