The answer is obviously number three. While none of these statements would appear to have any basis in fact, at least the first two won't sideline you with running injuries. Running is a great conditioner for many parts of the body. However, nothing worthwhile is without risk. In running the risk is muscular imbalance.
Muscles work in concert with other muscles.
Much like their owners, as long as these muscles maintain a strength relationship satisfactory to their partners, everything is cool. In the event that one muscle becomes too strong or rigid, tension develops and serious problems result. The best example of how muscular imbalance can ambush the runner is the hamstring muscle. It absorbs a tremendous amount of shock, and drives the act of running. A pulled hamstring muscle can bodyslam an Olympian onto a Tartan Track in a heartbeat.