A friend claims, by way of some argument that I can’t bring myself to understand, that you get more exercise running on a track than on a tread mill at the same speed. Something about the fact that the belt is moving, so you don’t have to use as much energy on a treadmill. I don’t know. All I know is, even though I get made fun of because I occasionally run on treadmills, I like them because unless I can see my pace, speed, distance, etc. right in front of me, I am unlikely to be very consistent, and thus get a good workout. So is there anything to this guy’s argument? Could it be explained any more clearly?
I’m with you on this. I’ve been doing a lot of my running on the TM recently. Just the other day, a PT over at the Wellness Center saw me on the TM and asked what I was doing on that. He said that it would take an Act of Congress to get him on a TM. (BTW, he was a sub 4-minute miler and has run marathons under 2:30.) However, when I really want to get some serious speed work in, the TM is the thing, for the reasons you stated. I can’t force myself to run very fast by myself, but the TM can get me to do that. Moreover, I’ve seen two top runners in this area use the TM. A lady runner, who always used to win the female trophy, told me that she was planning to do much of her running on the TM. Now that the weather is ideal here for running, I am doing most of my running outside, but I did the TM today, after tennis.
I’ve read extensively on running, including several books, including Dr. Noakes’ The Lore of Running. Many studies on runners have been done on TMs. The only thing that Dr. Noakes said is that a runner on the TM does not move forward and thus does not expend energy overcoming air resistance. I’ve also read that you should put the TM on a grade of one degree. All-in-all I think the TM is great when you are concerned about pace. In addition, you get the exact mileage covered and the exact time covered, not to mention fighting traffick, sidewalk cracks, street potholes, stopping for lights, avoiding pedestrians, bikes, etc. And in bad weather, it beats running outside.
Running on pavement makes my knees hurt 
The treadmill can absorb vibrations better.
No one’s saying that you don’t get any excercise from a treadmill. They are a great aerobic workout. But you will build the muscular endurance in your legs better by hitting a track. On a track, you’re using more of your leg muscles because you are providing your forward motion. On a treadmill, the ground is moving for you, so it’s a lot easier.
It’s like the difference between a gym’s “step mill” machine (the one that looks sort of like a small escalator) and a real set of stairs. On the machine, you’re not actually lifting your body by 8" or so with each step, so it’s easier than real stairs. Don’t believe me? Try doing 100 “floors” on a step mill in 20 minutes or so. You’ll work up a good sweat, and it’s certainly good exercise. Now try climbing the stairs in a 100-story building in 20 minutes. You’ll feel like you’re close to death, if you can do it at all. Big difference.
http://www.runnersworld.com/article/0,5033,s6-52-0-0-5915,00.html
20 reasons for running on a TM.
One percent incline on the TM: http://www.runningtimes.com/clinic/clinic.htm#treadmill
Well, here’s a 1.5% incline with a caveat regarding injury, contrary to other sources which state that the TM is safer: http://www.runningtimes.com/clinic/clinic04janjun.htm#speed_treadmill