I think there are not differences if you only run on the treadmill from time to time. But if someone runs on the treadmill exclusively for long periods, subtle changes (like more vertical displacement that i discussed with Marcel in the other thread) can start creeping into the gait. Also at slow speed treadmill and outdoor running is more similar than different. At higher speeds, while the treadmill is going at constant speed relative to the body, outdoors at high speed there is an acceleration and deceleration phase on each stride that effectively connect the successive “bounds” that make up running at fast speed. If you put your treadmill at 12 mph, and then if you run 100m in 19 seconds, outdoors right after that, you will feel the difference. Having said that, most of us are rarely running on the treadmill that fast, but even at 10 mph, there is an acceleration and deceleration on each stride…it is not entirely a constant overland speed between the body and land, whereas on treadmill it is.
And thats the bottom line. Whether people want to admit it or not, there are subtle differences (or no so subtle for some people) that exist once you get on a TM. Plain and simple. So I don’t understand why people vehemently argue that they are the same and they should pay no mind to it, just get on the thing. Its one thing to say, there are no differences so the science is settled, and quite another to say what you have just said, and what I and many others also say.
But to clarify your first point a little,** the differences are there the second you hop on the treadmill for 10 seconds or 10 hours. Its not that differences only exist once you start using it more than occasionally, its that the differences are always present and really only tend to become significant the more you use it (% of overall time running).** If your goal is to run a race outside then you should train outside because the more time you spend on a TM, the more those minor differences may lead to habits and altered muscle patterns. I use them too, but I use them sparingly because I don’t want to add any more variables to think about deep into my training blocks.
This is what Marcel and I pointed out in last year’s thread. Like any environment, we adapt if we do that exclusively. There are also subtle differences between tarmac and grass or tarmac and trail running and no one will debate that if one runs grass 100% that there won’t be an adaption period getting back to running on tarmac. It’s all running, but if we exclusively run in one environment, our brains will adapt to how we connect to the surface.
I had a good experiment this morning. I ran half of a 20 min treadmill run with vibrams and half with Hoka Cliftons. As you can imagine the sensation is dramatically different. I was on the treadmill and doing some short 1 min efforts. Here is something interesting…at 7 mph on a 12 percent grade the Vibrams felt easier than the Hokas. At 9.5 mph at 6% grade the Hokas were a lot easier than the Vibrams as the padding allows me to compress more actively at the front of my stride without any joint pain. I just can’t do that with Vibrams on. I can run slower with high cardio output on a steep inclines, but running fast with more pounding with Vibrams is hard on anything but grass. If I run exclusively with either extreme my gait would end up gravitating towards the optimal with each type of footwear to allow me to go fast. Now if I ran sprints with Hoka Cliftons on soft uneven grass, I am certain that I would be dramatically slower than sprinting on the same grass with Vibrams where I can do 20 second 100m surges (so a bit slower than 12 mph). I can never run that fast on a treadmill these days. I just can’t compress the front end of my stride enough without the belt slipping out under me too quickly.
Everything has slight changes running gait…surfaces and footwear. If we do exclusively one approach, we adapt to it. Then have to adapt back to something else.