It is common knowledge to hunters..(those who hunt for food and not just for 'sport')..that an animal which runs a lot, either before or after being shot, tastes more 'gamey' and tough because of the buildup of certain chemicals in the muscles. The quieter one has been, the more tender the meat. The famous (but very expensive) Kobe beef of Japan is bred for tenderness and processed carefully, sometimes being actually 'massaged' to improved quality.