My 84 Year Old Husband Walks On The Treadmill Every

My 84 year old husband walks on the treadmill every day for 40 minutes and has been doing so for more than three months. This morning he got a cramp in his calf, but, slowing his pace, continued to walk. The cramp moved to his thigh muscle. This was about seven hours ago and he still finds it painful tfor walk. Heat application does not seem to have helped.