Why do treadmills feel so hard?

   The "Ask Well" column in the New York Times recently addressed a subject we've broached in this blog before: treadmills are effective, painful, and boring!
    First, as far as effectiveness, I get my best workouts on the treadmill. Short intervals (10 x 800 at mile pace); long intervals (5 x 1600 at 5-K pace);  tempo runs (2 x 5000 at half-marathon pace); or an eight-mile run (marathon to half-marathon pace); each workout has a plan and purpose. Endorphin release? Not until I'm done.
   Most of my outdoor runs are the opposite. I head out one of a few familiar 6 or 7-mile courses, and just try to finish as quickly as I can. The runs start off at "long run" pace (about two minutes slower than 5-K race pace), and finish at tempo (about a minute slower than 5-k race pace).
   It takes about a mile to mentally and physically get into it, and then my mind wanders into a thousand different thoughts, ranging from the mundane to philosophical. I've remembered song lyrics and baseball line-ups that had long eluded me in the midst of long runs. I've solved a few problems and rationalized many others. I've re-lived many memories and done some thinking about the future, too. I've never come back in a worse mood than when I started. And no matter how hard I run, I always feel refreshed at the end.
    Ina 2012 experiment cited in the Times' article, people jogged on a track first, then went on a treadmill without speed displays and told to set it to a pace similar to what they ran outside. Almost all the participants picked a slower speed on the treadmill.
     Mechanically, treadmill running is easier than outside running, because there is less impact and you're keeping up with the speed of the belt, rather than creating your own energy. Yet, it feels much tougher!
   Researchers feel this is because the treadmills are inside, and the vitality you feel in the fresh air and outside elements can not be duplicated. Also, because the treadmills are a "walk to nowhere," there's not the same sense of accomplishment of actually covering a distance. I agree, and when on a treadmill, set it to "track mode," where it looks like you are actually circling the same 400-meter oval you do when running sprints outside. I can visualize making the final turn and "sprinting to the finish line."