The difference between running on the treadmill and running over ground can be discussed from mechanical, biomechanical and physiological points of view.
From the point of view of mechanics there is no difference between belt moving under our feet and our body moving forward in over ground running provided the velocity is the same. Indeed we are operating here with the same speed and consequently with the same forces on the ground and the same muscular efforts.
While it doesn’t matter for mechanics which of the interacting bodies is moving: the belt or the body, it is not so for biomechanics. It makes a big difference there. The major one lies in the fact that in treadmill running, unlike over ground running, our upper body is not moving forward, it’s our feet that are moved backwards by the running belt. This difference creates a different bio-motor pattern of the movement, where we have to produce some (otherwise undesirable) activity of the upper body to keep it against tipping over the support foot on the belt of the treadmill in order to keep the body in balance. So we have to hold our body to keep it from falling forward and we have to catch the running belt instead of our falling body.
In over ground running we need to free up our upper body from all possible tension in order to continue to produce the forward falling at the same rate and then recruit our feet to pull from the ground up in accordance with the rate of falling. In treadmill running, pulling the feet from the “ground” is dictated by the moving belt, which frames accordingly the space and time of the feet movement. The treadmill belt’s velocity helps us to maintain the rhythm and efforts of pulling in sync, the luxury we don’t have in over ground running. So while running on the treadmill we are not so much concerned with how fast and how strong we have to pull because it is pre-determined by the speed of the treadmill belt. In other words, treadmill running doesn’t require us to focus on pulling the foot from the ground as much as the over ground running does.
So, on the one hand, treadmill’s belt movement is a positive factor helping us to maintain our speed of running, but on the other hand, we do not have such a “help” on the ground and we have to manage the uneven speed of the body moving from one support to the other, which requires a much more sophisticated relationship between our feet and our body and consequently a much better neuromuscular regulation and coordination. It is well known that no one from elite athletes could match their treadmill running speed with over ground running on the same distance. The treadmill running is always faster because of the above-mentioned “help” from the running belt. That’s why most of them do not use treadmill for the training.
Another negative side of the treadmill running, besides the above- mentioned, is the risk of landing ahead of GCM and also neuromuscular coordination that’s too stable and developed by the stable velocity of the belt movement, up to the point of a complete loss of our perception of pulling in sync with our body falling, but not the belt moving, which helps us to move our foot from the ground in time. Consequently treadmill training affects our running on the physiological level as well.
Nevertheless, treadmill running is a good tool to do some training in the absence of suitable outdoor running conditions. It is possible even to do some Pose running drills there. Our level 2 coach from Toledo, Ohio, Joe Sparks, used treadmill to do his drills during wintertime with very positive effects on his outdoor running.
Treadmill running is also a good instrument for doing some physiological and biomechanical testing because it gives a possibility to standardize the condition of running and to control different technical and physiological parameters.