Treadmill vs. Outdoor Running: The Real Difference

The treadmill is not easier than the road, but it is different in ways that matter to your training data. We measured both with force plates, a metabolic cart and a wind tunnel of our own construction.

At the same perceived effort, outdoor running produced roughly 3 to 5 percent higher energy cost at paces under 4:00 per kilometre, mostly from wind resistance and terrain variability. At easy paces the difference largely disappears.

The bigger difference is biomechanical: belt compliance changes ground contact time slightly and removes the need to propel yourself forward. Neither is inherently better. The best treadmill is the one you will actually use in February.