Gravity and running

 

‘The great runner is not impervious to gravity; instead he taps it as a readily available source of free energy.’ Nicholas Romanov, founder of the Pose Method (in ‘Pose Method of Running, 2004 edition p62,)

‘All you’re doing is this (focussing on the central needle – the core of the body); gravity is doing the rest. You let gravity do its job and you get out of the way. The only thing the legs are for is for momentary support’ Danny Dreyer, founder of Chi Running,
http://www.youtube.com/watch?v=e-zrH6IOTQI

 

How should we to interpret these key statements of the theoretical foundations for Pose method and for Chi running. These statements cannot be literally true for running on a level surface. They violate the law of conservation of energy. As an object moves, the change in potential energy due to gravity is proportional to the change in height (http://en.wikipedia.org/wiki/Gravitational_potential_energy). If the height of the body’s centre of gravity at the end of each stride is the same as that at the end of the previous stride, there is no change in gravitational potential energy. The law of conservation of energy requires that any energy supplied by gravity at some part in the gait cycle must be re-paid at some other point in the gait cycle, and gravity cannot do the work required to keep us running.

My own belief, reinforced by the opinions of experts such as Dr Tim Noakes of Cape Town University, is that Dr Romanov has a remarkably good intuitive grasp of good running style, and hence his teachings should not be abandoned wholesale because one of his key theoretical statements appears mechanically unsound. So, how are we to interpret these statements about gravity?

If they cannot be accepted as literal truth, do they have any truth? Consider the saying: ‘the way to a man’s heart is via his stomach’. If this statement appeared in a training manual for aspiring cardiac surgeons, it would lead to surgical catastrophe, but in a ‘good home-makers guide’ it might lead to domestic bliss.

Dr Romanov, in an article posted in 2003 on PoseTech (http://www.posetech.com) makes it clear that he does expect the muscles to play a part: ‘By the pose method philosophy, muscles should just assist gravity in pulling us forward. Which doesn’t mean, of course, that we don’t need muscular strength, on the opposite, with the increase of the portion of gravity work we need much more skilful and powerful muscles to handle gravity.’ Maybe this implies that he intends us to adopt a mind set more analogous to that of the romantic homemaker rather that of the cardiac surgeon reading a training manual. The meaning might be in the image created rather than the literal truth. The image created might help harness muscular strength efficiently.

So what image might be created by the statement that we must get out of the way and let gravity do the work? By implying that the body will continue to progress forwards with only relatively minimal guidance from muscles, these statements encourage us to avoid pointless muscle action which is both wasteful and potentially injurious. ‘When you master the Pose method you will experience the incredible Lightness of Running’ (Pose Method of Running, 2004 edition, p 42). In fact because of Newton’s first law of motion, (a moving body will continue to move in a straight line at constant velocity unless acted upon by a force) a direct propulsive force is not required to maintain a constant pace when running on a level surface in the absence of wind resistance. However, because we run upright on two legs rather than rolling like a billiard ball, we do have to move our legs rapidly forwards in each stride if the body is to remain supported in an approximately upright orientation. The goal of efficient running is to move the legs forward rapidly enough to prevent a face-down fall in a way that uses minimal energy with minimal risk of injury. A focus on minimizing muscle action makes sense.

Dr Romanov emphasizes the incredible lightness of running – in other words, minimizing the impact of gravity which tends to pull us to earth with a thud. So if we are to achieve this incredible lightness we need to understand the points within the gait cycle at which gravity is likely to play a strong role.

Free-fall while airborne
Gravity is at its most remorseless when we are airborne. It is inevitable that we will fall freely during this time. Gravitational potential energy is converted to kinetic energy that will bring us forcefully into contact with the ground at foot-strike. At this point, some of the energy can be captured in the stretching of the quadriceps muscles, provided the knee is slightly flexed, and in the muscles and tendons of the foot and calf, provided we land on the ball of the foot. These are features of the Pose style. The stored energy can be recovered by elastic recoil as the foot is lifted from the ground at the end of stance. However, some energy will inevitably be lost, so one of the cardinal goals of efficient running is to minimise the amount of free fall. Because the speed of falling increases with longer duration of fall, less energy will be lost by a series of frequent short airborne periods than by series of fewer longer airborne periods, of the same total duration. Hence high cadence is essential. For a mathematical proof of this, see the calculations page in the side bar.

Footfall
What about the foot fall itself? Because the leg begins to fall while the body is already falling, gravity is unable to pull the foot down relative to the trunk. A very light muscular action is in fact required. However, consciously forcing the foot down creates a grave danger of excessive force. The task of applying the slight force to bring the foot down while simultaneously adjusting muscle tension in a way that establishes sufficient tension in the muscles of the thigh to stabilise the knee is beyond conscious control. Fortunately, by virtue of learning to walk in the omnipresence of gravity, we have already acquired a great deal of automatic skill in summoning the right amount of force. If we are applying too much force, foot-strike will generate a thudding sound. However, the incredible lightness of running described by Dr Romanov cannot be attained by conscious adjustment of muscle tension; rather it is done by listening to the sound of foot-strike and simply aiming to reduce the thud to a light patter. Our brain has a remarkable capacity to adjust muscular activity to produce the goals we set for it.

While on stance
Once the foot is on the ground, gravity serves one useful goal: it tends to anchor the foot in place and minimizes the risk of slipping. However, now our body will begin to rotate in a head forward and downwards direction because our trunk is carried forwards by momentum, while the foot is stationary. This rotation unbalances the body and after a short period, will stimulate a reflex action that lifts the foot from the ground and initiates the next swing forwards. This lift-off can be promoted by conscious effort, and indeed a strong intentional pull is essential if we wish to run fast.

As the long axis of the body rotates away from vertical during the early part of the stance phase, gravity will have a component at right angles to the axis of the body and therefore, will tend to increase the speed of rotation. Dr Romanov suggests that this effect of gravitational torque offers a free source of energy. However by virtue of the law of conservation of energy, any energy gained from gravity at this point of the gait cycle must be paid back at some other point in the gait cycle. Furthermore, according to the calculation presented on the calculations page (in the side panel), the amount of acceleration due to gravity is relatively small, at least until the lean becomes quite marked.

The gravitational torque induced by the transient marked lean as a sprinter drives from the starting blocks almost certainly plays an important part in generating the rotational motion that stimulates rapid and forceful lift-off from stance. However, in my opinion, during steady running at the more moderate pace of the long distance runner, the contribution of gravitational torque to destabilization is likely to be small relative to the contribution from forward momentum. Even if the degree of lean is sufficient to produce an appreciable contribution of gravitational torque to the de-stabilization, this energy would have to be paid back, and it cannot be regarded as a free source of energy. So, I suspect that gravitational torque generated while on stance plays at most a very small part in running.

Conclusion
Where does this leave the teaching of Dr Romanov and Danny Dreyer regarding gravity. The crucial importance of their contributions is their emphasis on running lightly. In practice, they offer several very useful suggestions for achieving this. In Pose Method, the recommendations are:Run with a high cadence to minimise free fall. Land with the knee flexed, and on the ball of the foot, to absorb the energy of impact in quadriceps, and the tendons and muscles of the foot and calf. (But allow the heel to touch the ground to prevent excessive load on the Achilles tendon). Spend a short time on stance to promote efficient recovery of this stored energy through elastic recoil. And if your ears tell you that you are not running lightly, simply focus your mind on achieving lightness. The brain will do the rest.

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5 Responses to “Gravity and running”

  1. Bill McGuire Says:

    Canute, great stuff. I have been running in the Pose style for almost three years and I enjoy it immensely, but I welcome questioning about the way Pose is presented, if you catch my drift. Which I assume you do.

  2. richh Says:

    At least three things are going on:
    1. What our bodies are actually doing and what we them them to do.
    2. Our thoughts and images, as they affect what our bodies are doing.
    3. Coaches words and actions, as they affect our thoughts and images.

    Statements about gravity by Romanov, Dreyer, et al. may not be literally true, but they can change our thoughts in ways that help our bodies move better.

  3. canute1 Says:

    Bill Mcguire, Thanks very much for your comments on this and other recent posts.

    richh, I agree that the images created by Dr Romanov and Danny Dreyer can be very helpful. Indeed, that was the main conclusion of my article. However, there is a sub-text, perhaps implied in the comments of Bill McGuire. It can be very frustrating (and potentially injurious) for a student to be told some things that are intended as literal truths and other things that are false but might nonetheless evoke useful images, within a context that implies that all of the information is literally true. This is especially a problem for the student who purchases a book or DVD in good faith but does not have easy access to expert coaching. In that circumstance, he/she must also assume the role of his/her own teacher, and teachers who do not understand the material they teach are likely to be poor teachers.

  4. richh Says:

    Canute,
    I agree with you. I, for one, would feel better served by a coach saying, for example, “You should strive to feel that you are landing directly under your GCM, although in fact you will land a bit in front – try to minimize this ‘bit in front”” rather than having him say, “Land under your GCM.” Other runners may not be as picky and literal-minded as am I. Part of the art & skill of coaching is to adapt the teaching method to the student – obviously much harder in the context of a book or DVD than in person. That said, the POSE book worked for me (the DVD gives me a headache).

  5. Greg Davidson Says:

    This is something I can think about the next time I go out for a jog.

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