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Treadmill Running vs. Natural Running – how they differ in affecting sports performance
Treadmill running and natural running differences
Q. I was very interested to read Owen Anderson’s recent piece about treadmill training (PP164, May 2002). Clearly there are differences between treadmill running and natural running, the biggest being the effect of wind resistance: running at 5m/sec on a treadmill is equivalent to running in a 5m/sec following wind in the open air.
But what other differences are there? The surface of a treadmill feels not dissimilar to an all-weather track, so that can’t make much difference. And the way one has to run round bends, cope with uneven ground and vary pace more in normal running is surely not enough to account for the ‘biomechanical and kinematic differences’ you refer to.
So how can they be explained? Elementary physics tells us that all that counts is the relative velocity of the runner and the surface on which he is running, and that whether the ‘ground’ is stationary or otherwise is irrelevant. Leaving aside the question of wind resistance, the physical equations are the same whether it is the ground or the runner that’s moving.
If you are not convinced of this, imagine a treadmill the size of a tennis court or a football pitch (or even the whole of New York City): except for the effect of the wind, it wouldn’t matter in what direction you started running on it in a straight line until you got to the edge of it and fell off; it would feel the same and, in physical terms, be the same.
However, anyone who’s done it knows that we do run differently on a treadmill from outside. Why? If it’s not physical it must be psychological and, yes, looking at the gym wall and a digital display is quite different from looking at the road or track ahead. At first, as in the Australian study Anderson referred to, you shorten your stride as if you’re afraid of running into the wall. After a while you find that the steady predictability of the treadmill enables you to stretch your stride, as did the experienced runners in the Penn-State study. It all figures.
And here we cut to the chase. Several of the studies Anderson referred to find that treadmill running is significantly less costly than normal running, even after allowing for the wind factor. In his penultimate paragraph he describes the difference in running style involved and quotes the surmise of some experts that, essentially, to run more cheaply one should do more work from the knee down and less from the knee up.
So, if that’s it, all that’s required to improve your running economy is to imagine you’re running on a treadmill and that the ground is streaming by beneath your feet. Could it really be that easy? I think I’ll try it. Any comments?
A. As you correctly point out, one of the biggest differences between treadmill and natural running is the effect of wind resistance. However, I am afraid it is not logical to assume that, since treadmill and natural surfaces feel similar, the impact forces and energetic costs associated with running on the two surfaces must also be similar.
The impact forces which are present during treadmill running have been very poorly quantified in scientific research. And, indeed, they must vary from treadmill to treadmill, depending on the support structures beneath the treadmill belt. One cannot simply assume that these forces and costs are the same as those that apply on the ground or track. Furthermore, I should point out that for many athletes treadmill and normal running feel quite different. Although perceived hardness and impact forces are not infallible guides to true forces and energetic costs, it is quite possible that there are significant differences in these variables on treadmill and track or road.
A treadmill the size of New York City
Regarding your next point, I have indeed imagined a treadmill the size of New York City, and doing so has no impact whatsoever on my basic argument that treadmill and normal running are fundamentally different. The size of the treadmill is absolutely irrelevant.
Here’s why: if you think about it for a moment you will realise that the treadmill itself and the runner on the treadmill are both moving at the same speed – the speed imparted by the rotation of the earth. The net velocity of a treadmill runner in relation to the overall treadmill is zero. However, a treadmill belt (unless it is not activated) is not moving at the same velocity as the runner. If the belt speed is set at 10mph, for example, any specific point on the treadmill below is moving away from the runner at a velocity of 10mph. That backwards motion is interrupted by the ‘recycling’ motion of the treadmill belt, but you get my point: the length of the belt and the overall size of the treadmill do not matter; the net difference in velocity between runner and belt will be 10mph.
When a foot hits the treadmill belt while running, the foot, ankle and shin, being momentarily ‘parts’ of the belt, will move backwards from the centre and mass of the body at the same speed as the belt – 10mph. This must be true unless you think of the human body as a rigid rod without segments or joints, in which case the centre of mass would also move backwards at the same speed. However, research indicates that during treadmill running the shin of the support leg is less erect at contact and moves through a greater range of motion, with a faster overall angular velocity, than in normal running. If footstrike time averages 180 milliseconds (an average for good-quality runners) then the foot could move backwards in relation to the centre of mass by about 2.6 inches during treadmill footstrike. (It will actually be a little less than this, since the centre of mass and upper body will tend to be dragged along at least a little.)
I think you are correct in believing that psychological factors may play a role in determining the physiological cost of treadmill running. However, your interpretation of the experience of the Australian joggers and veteran Penn-State runners is not quite correct. Both groups had roughly equivalent experience on the treadmill; the difference was that the Penn-State runners had much more experience running on normal ground.
There are several documented ways to improve your running economy, including hill training, strength work and training at vVO2max. I believe that proprioceptive training also enhances economy. Psychological strategies are also probably effective for some runners, and it may well be that thinking of the ground as streaming beneath your feet can help create a more relaxed and economical running form.