Where should the foot land?

One of the key principles of efficient running advocated by Gordon Pirie, and subsequently incorporated as a major feature in other styles such as the Pose method of running developed by Dr Nicolas Romanov, is the principle that the foot should land under the body. (See p16 of Pirie’s book ‘Running Fast and Injury Free’). At first sight this makes sense since placing the foot beneath the body, with the foot moving backwards relative to the centre of gravity (COG) such that the velocity of the foot relative to ground is zero, will minimize braking which would waste energy while increasing the risk if injury.

Pirie is emphatic about the importance of avoiding landing with the foot too far forward. He warns: ‘over-striding is one of the most common technical afflictions of runners and one of the most dangerous’ (p18).

However, observation of elite athletes, such as Haile Gebrselassie (http://www.youtube.com/watch?v=_xGXPxJzeug ) reveals that they often land a little in front of the COG. An elite athlete probably does this automatically, but if we assume that one of the characteristics that makes an athlete elite is the ability to sense what is most efficient intuitively, it suggests there might be a reason why landing in front of the COG is actually more efficient.

A clue is provided by consideration of the torque that will be applied by gravity during the stance phase when the foot is on the ground. Once the COG passes in front of the point of support, the body is unbalanced and gravity will exert a torque that tends to pull the head forwards and down relative to the feet. In fact Dr Nicholas Romanov argues that this torque provides useful forward propulsion. I am dubious of this claim because gravitational torque will tend to generate angular momentum (rotational movement) rather than linear momentum (forward motion). Whatever the fact of this issue, there is an even more important issue to consider. If gravity applies torque that increases angular momentum, then this torque must be reversed at some point in the gait cycle or the rotation would continue to accelerate and the runner would end up face down on the ground after a few strides.

So, granted that once the COG has passed in front of the point of support gravitational torque promoting a face-down crash is unavoidable, we need to ask where in the gait cycle an opposite torque might be applied. One answer would be to land with the foot a little in front of the COG so that for a brief period the gravitational torque acts in the opposite direction. This might seem to provide a plausible explanation for the observation that elite athletes often land a little in front of the COG, and also emphasizes that struggling to adjust one’s style to land directly under the COG might be both pointless and possibly dangerous.

 

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5 Responses to “Where should the foot land?”

  1. Jhuffman Says:

    Canute,

    I am curious as to why you only seem to want to emulate Haile’s running form. Why not emulate one of the many other elite distance runners?

  2. Jhuffman Says:

    Canute,

    Intuitively the support of any structure is best supported by having the CM being directly over the point of support. So, why would you assume that landing in front of the COG/GCM is good or bad just because an elite runner does this to some extent. To me it makes more sense that anyone who lands ahead of the COG/GCM that it will create a less than ideal position for support of the body. And since we know that our body must move to this point regardless of technique we choose to emulate, I don’t understand why you postulate such and arguement to begin with……

  3. canute1 Says:

    Jeremy,
    I agree that landing in front of the COG presents a problem due to the braking effect which might waste energy and increase the risk of injury. Therefore, I did not start from the assumption that landing with foot in front of the COG is good, but I was forced to consider the possibility that it might be necessary to prevent a face-down fall. Unless the length of time on support is zero, then the body will move over the point of support during the stance phase, and so we must spend some time off balance. As described in my blog on where the foot should land, when the COG is in front of the point of support, gravity exerts of force that creates a torque that rotates the body (head forwards and down). Dr Romanov argues this torque is useful. However, it raises a problem. Unless the torque is reversed at some stage in the gait cycle, a face down crash will occur. That is why I raised the possibility that landing in front of the COG might be necessary, because it would create torque in the opposite direction. There might be other possible ways of applying reverse torque, such as active flick of the foot at lift-off which could produce the required reversed torque. I will attempt to calculate which is the most efficient way to apply the reverse torque in the near future.

  4. Bill McGuire Says:

    Canute, Jack Becker, who is the main guiding voice on the Pose forum, has suggested a few times that landing a little in front of the COG is acceptable. I can’t say for sure, but I suspect his reasons are based on his formidable intuitive feel for Pose more than on mathematics. But still…

  5. canute1 Says:

    Bill, I agree regarding Jack Becker’s formidable intuitive feel for Pose, and I believe he is absolutely correct to suggest that we should land a little in front of the COG. I will post a full explanation for my belief in my blog later today.
    Canute

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