I've had a few years off running properly, thanks to back to back pregnancies and breastfeeding, but I'm now back on the exercise train and have been so enjoying getting out - except that my knees are really complaining afterwards. I've just had a couple of weeks break after a longer run caused them to ache for days. I want to keep going - is there anything that will help? Or must I accept that my 40 year old knees are no longer up to the job?