Using a treadmill gives you the same health benefits as walking in the great outdoors. While there are a couple of variables that can alter the duration of a 3-mile walk on the treadmill, it will take about 45 to 55 minutes to complete that distance at a moderate pace.
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Speed and Incline
Speed and incline are the two game-changers when it comes to time spent on the treadmill. If you're doing a 3-mile walk, which is a manageable distance for most people in average or good shape, then increasing or decreasing the speed will shorten or lengthen the amount of time you spend walking. By the same token, adjusting the incline will have the same effect; if you raise the incline for uphill walking, you will likely complete your walk at a slower pace.