While the allure of the gym — climate-controlled, convenient and predictable — is obvious, especially in winter, emerging science suggests there are benefits to exercising outdoors that can’t be replicated on a treadmill, a recumbent bicycle or a track.
You stride differently when running outdoors, for one thing. Generally, studies find, people flex their ankles more when they run outside. They also, at least occasionally, run downhill, a movement that isn’t easily done on a treadmill and that stresses muscles differently than running on flat or uphill terrain. Outdoor exercise tends, too, to be more strenuous than the indoor version. In studies comparing the exertion of running on a treadmill and the exertion of running outside, treadmill runners expended less energy to cover the same distance as those striding across the ground outside, primarily because indoor exercisers face no wind resistance or changes in terrain, no matter how subtle.