A treadmill doesn't work your hamstrings and glutes or burn as many calories as much as walking outdoors since the propulsion of the treadmill does some of the work for you. But you can compensate for that by increasing the incline of the treadmill. The treadmill is easier on your joints though. There are advantages to being out in nature too. But they're great for rainy and snowy days. I like to listen to podcasts while on the treadmill. Makes it a little less boring. :-)