It was the shoes which proved to be the weak link. I used to do sprints on the treadmill with the same shoes with which I lifted weights. They were hiking Solomon hiking shoes which didn't do much for my foot (check Vibram Five Fingers - radical footwear.) I damaged my heel. During the recovery, a nearby house caught fire. While trying to help I damaged the heel even more. It didn't help that I live on the second floor and have a habit of climbing steps running. The prolonged heel damage some how affected the quads also.
I was pretty ok for a year or so but about three months back the quads started acting up again. I tried the physiotherapy which didn't help. I recently read this article on the heart scan blog which had this interesting article on creatine. The expense is a deterrent (imported stuff at twice the original price) but seems worth a try.
The Heart Scan Blog: Creatine: Not just for muscle heads:
Even if you’re not interested in building big muscles like a bodybuilder, there are health benefits to increasing muscle mass: increased bone density, better balance, and fewer injuries. Greater muscle mass means higher metabolic rate, improved insulin responsiveness, lower blood sugar. The inevitable loss of muscle mass of aging can lead to frailty, an increasingly common situation for the elderly. Muscle loss be reversed, health improved as a result.