The conventional wisdom is that if you routinely do long distance running, it will break down muscle tissue, and the runner will lose both fat and muscle mass. However, if you sprint, that should help build muscle, especially if you aren't particularly muscular to start with (e.g., a distance runner who has never been more for weights). Sprinting may not be as anabolic as the weight room, but it is still anabolic, right? And assuming it is, where is the line between catabolic running (i.e., you lose muscle) and anabolic running (i.e., you gain muscle or at least won't lose any)? How far can one run without running becoming catabolic?