I often get asked, "Does running build muscle?" Usually my answer is no, but with a caveat: regardless of the type of training—whether bodybuilder or power lifter, purely for size or strength, or for a particular sport—running has its place. What's key are the type and duration. Long distance running rarely fits in to any of those plans. (Here's how to tailor it for your sport.)
As a power lifter, for example, you're trying to max out your leg strength with low rep squats. Running for miles on end will compromise your recovery and maybe even decrease your leg strength. Some wrongly mistake leaner legs for stronger ones. Although running may trim some of the fat off your legs, it's not likely to make them stronger.
If you're a triathlete or a marathon runner, by all means run for long distances to build your endurance. However, for most athletes who want to build muscle and maintain conditioning, there are better alternatives. Long distance runs don't make sense for strength athletes or for football, baseball and hockey players. Those sports require sprinting in 60- to 90-second intervals, so you should train in ways that prepare you for that type of running. How? With high intensity interval training.
This can mean anything from straight up 60- to 100-meter sprints to sled pulls or hill sprints. Sled pulls, for example, mimic a hockey player's all-out 60-second shift on the ice, a punt returner's sprint down the field, or a baseball player's run around the bases. You have the resistance of a defender (in the form of the sled) with the cardiovascular element of a full-out sprint. (See powerhouse RB Trent Richardson's explosive running training.)
You want to build explosive power, and yet still be able to train in the gym and build muscle during your down time. Try running five miles a day combined with daily strength training in the gym, and see how quickly you burn out. Also, the calories you'd have to consume to grow muscle would be significant, considering the calorie deficit created by the run.
So does running build muscle? With a combination of HITT (running in sprints) and weight lifting, you can build the endurance required for your sport without cutting into the strength gains you need to make to last you through a long season.