Originally Posted by
prj71
That and running is hard on joints and you'll pay for it later in life. I have so many friends that were long distance track runners in high school and their 20s and then continued to run later on in life and now in their 50's and 60s are paying for it.
This is only true if you're running some very high mileage. For most people, including cyclists doing it as cross training, it's fine and may even have a protective effect.