Runners World: Running V. Walking How Many Calories will you burn, http://www.runnersworld.com/weight-loss/running-v-walking-how-many-calories-will-you-burn
Runners World: How Many Calories are you really burning, http://www.runnersworld.com/weight-loss/how-many-calories-are-you-really-burning?page=single
Active: Running Versus Walking Which Burns More Calories, http://beta.active.com/running/articles/running-versus-walking-which-burns-more-calories
Active: Indoor vs. Outdoor Running, http://beta.active.com/running/articles/indoor-vs-outdoor-running-3-things-to-know-about-treadmill-training
Runners World: How Effective is Treadmill Running Compared to Running Outside, http://www.runnersworld.com/beginners/how-effective-is-treadmill-running-compared-to-running-outside