I was a running addict – but pushing myself to the limit led to two knee replacements | Rod Gilchrist

Beware what the fitness gurus tell you: the body has its limits. Perhaps that's why orthopaedic waiting lists are so long

I am preparing for an anaesthetist to sink a hypodermic needle into my back at a busy London hospital ahead of a scheduled surgery to replace my knee. Knowing this might be painful, I ask a fellow patient how he got his mind around the jab. Two spliffs of good dope worked for me," he confessed. I'm yet to try that, but this is my second left knee replacement in less than 15 years - an increasingly common story as our population ages and obesity levels cause growing strain on our joints.

More than 2m hip and knee replacements have been performed in the UK since the early 2000s and waiting lists continue to grow. By 2060, demand for hip and knee joint replacement (based on data for England, Wales, Northern Ireland and the Isle of Man) is estimated to increase by almost 40%.