running outdoors burns more calories... (Read 448 times)

True and false. Studies have shown that differences in the oxygen and metabolic cost of running (energy expenditure) on a properly calibrated treadmill at zero incline vs. outdoors on flat terrain with the same climatic conditions (temp, humidity and calm wind) due to the lack air resistance is insignificant when running slower than 6:00/mile. See The 1% Incline Treadmill Myth for details. Studies are conducted under carefully controlled conditions. In the real world, treadmills are often miscalibrated (which can make them harder or easier than running outdoors with all other conditions being equal), outdoor terrain and climatic conditions can vary widely relative to the indoor conditions of a treadmill (which can make outdoor running easier or harder), and treadmill inclines and speed can be adjusted to make treadmill running energetically "equivalent to" outdoor running under any conditions. So, if the treadmill is properly calibrated (a big "if"), you set the treadmill incline at zero percent, you set the treadmill speed faster than 10 mph (if it will go faster than 10 mph), and the outdoor conditions are the same as indoors, then the article is right. Otherwise, it's another sound bite example of eye-catching, over simplified horse hockey.