Are you just starting out with running? The key with running, especially if you are just beginning, is not to over do it. Most people start running and burn out or have a pre-mature muscle injury because they over do it. I would consider talking to a running shop in your area or talking to some experienced tri guys/gals. Keep us posted on what you decide to do. I would like to know what other info you gather or get told. I worked with a few triathletes and are pretty good friends with them now. Happy to ask them any questions for you.