I used to be a runner in my 30, averaging about 18 miles a week…it saved my life. Now, at age 72, and 15 years after my triple bypass, I was doing 3 miles walking on the treadmill every other day…running is very hard on your knees and back…I had to stop for a few months after my the lower part of my lungs collapsed (atelectasis)…I am getting back into walking, working on 2 miles every other day. If you are starting to run, you must pay attention to the aches and pains…listen to your body…there is a huge difference between running with pain and running with injury.