I won’t get into the physics behind treadmill running because I don’t know enough about about physics to make a solid argument. However, those that say you don’t have to push off and propel yourself forward are kidding themselves. If you jump up in the air on a treadmill you will go backwards unless you try to propel yourself forward. That is a fact.
Now, all this doesn’t really matter. The bottom line is you can get a very good workout on a treadmill. Comparing treadmill running paces and outdoor running paces is pointless, however. Because of calibration differences, style differences, temperature differences, and the previously mentioned bio-mechanical differences between the 2 it is impossible to say whether one is easier. I train every run on the treadmill and I make sure it is on the same model of treadmill at the gym every time. This allows me to compare workouts and judge improvement. It does not, however, convert directly to outdoor performance. Oct. 30th I did a 15K after having not run faster then 7:30 treadmill pace in over 3 weeks. I was running most of my mileage in the mid-8’s per mile on the treadmill as well (all at a 1% grade). I ran 1:04:53 or just under 7:00/mile for 9.3 miles. Obviously for me treadmill running is much slower then road running and has been consistently. The key to treadmill running to me is, forget about road pace and find your treadmill pace (and that treadmill pace is only accurate for that treadmill…another treadmill may be different). Then you can train all you want on them and you will improve on the roads. Is treadmill running better? I would say no, but for those of us with bad-knees it may allow us to run more often and more miles. More consistent training equals better results. Thats been my experience and I will continue to train exclusively on the tread until I can out-run its top speed.