In my post on 8th Feb I described how the Pose Method of Running has strongly influenced my understanding of running style. In that post I focused mainly on the features of Pose that I have found helpful. Here is a summary of those features:
1) Running style matters for all runners; amateurs whose major goal is to enjoy running injury free and elites who are eager to maximize their speed and efficiency.
2) High cadence, at least 180 steps per minute, is efficient
3) Short time on stance maximizes both speed and efficiency; short time on stance demands landing only a short distance in front of the centre of gravity
4) Landing on the ball of the foot is efficient and can reduce risk of injury to joints, especially hip and knee.
5) When making changes to running style, it is sensible to employ drills to make the new style habitual and exercises to develop the strength required to sustain the new pattern of motor activity.
I will return to consider most of these positive features in greater detail in the future, but now it is time to address what appear to me to be negative or misleading aspects of Pose.
The metaphor of gravity as the source of energy
The role of gravity is central to the theory of Pose, but it is not all that easy to determine what Dr Romanov believes about gravity. In the first chapter of Pose Method of Running he states that we should use gravity as the source of energy. Elsewhere he talks about gravity providing propulsion for running. The statement that gravity is the source of energy must be taken as a metaphor: words that invoke an image rather than words that are literally true. This image might well be useful, but confusing metaphor with reality can be misleading. Gravity can be a source of kinetic energy only if the centre of gravity of the object falls. Over the course of the gait cycle, the body does not fall so gravity provides no net energy.
At Loughborough in 2008 when I had endeavored to engage him in discussion about the role of gravity, Dr Romanov had been unwilling to discuss this issue, but by 2009 he was prepared to acknowledge explicitly that gravity is not literally the source of energy for running. In a presentation on accelerated running presented at the 22nd ISBS conference in Limerick, Ireland, in 2009, Dr Romanov and his colleagues acknowledged that: ‘Gravity completes no net work during stance in constant speed running,’ [This paper is available at http://w4.ub.uni-konstanz.de/cpa/article/viewFile/3291/3092]
Dr Romanov further obscures the meaning of the statement in chapter 1 of Pose Method of Running that gravity is the source of energy, by use of misleading analogies. In chapter 12 (page 64) he compares the deflection of the vertically acting force of gravity to provide horizontal propulsion for the runner with the way a yachtsman sets the sails to utilize the wind to propel a boat into the wind. However, this analogy is misleading and largely irrelevant because the pressure of wind on the sails imparts energy to the boat; the setting of the sails deflects the direction of the force, but the crucial issue is that the wind provides energy. Elsewhere in Pose Method of Running (page 210) he uses the illustration of a lumberjack felling a tree on a hillside so that it falls in the uphill direction as a description of how Pose allows a runner to use gravity to propel him or herself uphill, but fails to point out that the felled tree ends up with its centre of gravity lower after being felled, whereas the uphill runner must raise his or her centre of gravity. So these analogies do not explain how gravity might provide the energy for running.
Pose, fall, pull
Behind the smokescreen of misleading analogies and motivational material such as accounts of the achievements of Tiger Woods and Lance Armstrong, Pose Method of Running does provide a description of the core of the Pose technique, which can be summarized in three words: ‘pose, fall, pull’. At mid-stance, for a brief instant, the Pose runner adopts the posture which Dr Romanov calls the pose. This is a position in which the ankle, hips and shoulder are aligned. The knee is slightly flexed so the legs and torso form a shallow S shape. Although momentarily in balance, this posture is poised on the brink of instability. Slight forward movement results in a face forward-and-downwards fall, driven by gravity. As the body rotates forwards and down, the weight is taken off the foot, allow the pull: a swift hamstring contraction that pulls the foot towards the buttocks. The body is now airborne and moving forwards towards the point at which the other foot is allowed to drop to the ground virtually under the centre of mass, with the point of support under the ball of the foot; and from footfall the body moves to the next pose, fall and pull. At first sight this might seem plausible.
The common-place experience of leaning forwards from a standing position to commence running makes the sequence of pose, fall and pull appear plausible. Indeed the Pose description does capture some of the features of accelerated running moderately well, though even in accelerated running gravity is a stimulus to promote muscle contraction rather than a source of free energy. But when it comes to running at a steady speed on a level surface, the sequence of pose, fall and pull does not describe the essence of how we run.
What is missing from pose, fall, pull?
First of all, the unbalancing after midstance is due mainly to momentum. In fact, once one is up to speed, momentum carries us forwards, as dictated by Newton’s first law of motion. Forward propulsion is only required to overcome wind resistance and to compensate for the braking that occurs in early stance. The major energy consuming actions of running are getting airborne and swinging the leg forward fast enough so it is ready to support the body at the next footfall. By focusing on the proposed role of gravity in providing forward propulsion when running at constant speed, Pose focuses on one of the aspects of running that consumes relativley little energy, apart for the situation when there is a very strong headwind. Furthermore, in attributing the forward propulsion to gravitational torque, Dr Romanov is almost certainly wrong. Gravitational torque in late stance generates a forward-and-down rotation, not a forward linear motion. If a face-down crash is to be avoided, this rotation must be corrected at some other point in the gait cycle.
At least part of the cancellation of the head forward-and-down rotation is provided by the oppositely directed gravitational torque that acts in early stance. A calculation based on force plate data acquired by Cavanagh and Lafortune which I performed during my debate with Simbil in the comment section of my post on Feb 24th, 2009, demonstrated that about 2/3 of the head forward-and-down rotational momentum was cancelled by the oppositely directed gravitational torque acting in early stance. I consider it probable that the remaining one third of the rotational momentum in that instance was cancelled by the wind resistance, but in the absence of a precise measurement of wind resistance, that remains speculation. Nonetheless, the central issue is that gravitational torque cannot generate forwards linear momentum. According to Newton’s second law of motion, linear acceleration in a forward direction at any instant is proportional to the forward directed forces acting on the body at that instant. Apart from wind, the only horizontal force is the horizontal component of ground reaction force (GRF), and that must be the source of forward propulsion.
It should be noted that recording of the electrical signals associated with muscle contractions demonstrate that the major extensor muscles of the leg which might be expected to push against the ground to generate the forward ground reaction force are largely silent in late stance. However force plate data (eg Cavanagh and Lafortune, Journal of Biomechanics, 1980) clearly demonstrated that there is a forward directed horizontal GRF in the second half of stance. The push that generates this is the elastic recoil of muscles that had been subjected to eccentric contraction in early stance. The Pose emphasis on gravitational torque fails to acknowledge the role of horizontal GRF in providing the forward propulsion that is required when maintaining a constant speed.
A further illustration of Dr Romanov’s under-estimation of the role of horizontal GRF is provided in the paper by Fletcher, Dunn and Romanov on accelerated running presented in the ISBS conference in Limerick in 2009. In that paper the authors present data which they claim shows that maximum horizontal acceleration of the centre of mass (COM) occurs before maximum horizontal GRF. They conclude that acceleration of the COM occurs via a gravitational torque with GRF being the consequence of, not the cause of these movements. In contrast, equation 1a in that same paper correctly shows that the horizontal acceleration at any instant in time is proportional to horizontal GRF (in accord with Newton’s second law) and hence the maximum horizontal acceleration must occur at the same time as the maximum horizontal GRF. The author’s conclusion appears to be in direct contradiction to equation 1a and to Newtonian mechanics.
As stated above, when running, the issue of horizontal propulsion is not the major issue. From the point of view of energy consumption, getting airborne is a bigger issue. Pose theory emphasizes the role of a pull by the hamstring that pulls the foot towards the buttocks. I find this concept of the pull interesting and believe that conscious focus on producing the pull as recommended by Dr Romanov is indeed very helpful. However, a hamstring pull cannot lift the body – that would be like lifting oneself by one’s own bootstraps. The force that gets us airborne is the vertical component of GRF. Force plate data demonstrates that through most of the stance period vertical GRF is much greater than body weight – typically 2 or 3 times body weight. In late stance, the silence of the extensor muscles implies that GRF is maintained by elastic recoil of muscles and tendons that had been subjected to eccentric contraction in early stance.
Dr Romanov’s serious under-estimation of the magnitude of GRF is illustrated in figure 7 in the article by Romanov and Fletcher in Sports Biomechanics, 2007 (volume 6, pp 434-452) entitled: ’Runners do not push off the ground but fall forwards via a gravitational torque.’ Figure 7 illustrates the forces acting during the part of stance after the centre of mass (COM) has passed over the point of support. The authors conclude that the resultant force acting on the body is equal to the component of gravity at right angles to the line from point of support to the COM. They base this conclusion on the statement that the component of gravitational force along the axis from support to COM is equal and opposite to the ground reaction force vector. Force plate data such as that presented by Cavanagh and Lafortune clearly demonstrate that this is simply wrong. Throughout most of stance GRF is much greater than body weight, and it is the vertical component of this GRF that gets us airborne.
In the figure showing forces acting on a runner after mid-stance, diagram (a) depicts fig 7 in Romanov & Fletcher (Sports Biomechanics, 2007). GRF is cancelled by the opposing component of gravity. The resultant force (thick black arrow) is equal to the forwards and downwards component of gravity. Diagram (b) is based on a more realistic estimate of GRF (from Cavanagh & Lafortune, Journal of Biomechanics, 1980). GRF exceeds the opposing component of gravity. The resultant force (thick black arrow) is directed forwards and upwards.
Insofar as Pose theory encourages an under-estimation of the magnitude of ground reaction forces, it creates an illusion that puts us at risk of failing to develop adequate strength of muscle and sinew to withstand forceful eccentric contraction, and thereby to store adequate elastic potential energy which can produce the recoil required to generate both the horizontal GRF that provides the required horizontal propulsion and the even larger vertical GRF that is required to get us airborne. Failure to develop the required strength will result in sub-optimal performance and might place us at risk of injury.
Physics is not the only science
On the other hand, it is not purely a matter of physics. In fact the human brain processes intended whole actions rather than muscle contractions. With its focus on a rapid pull, the imagery (and drills ) of Pose can facilitate a remarkably rapid lift off from stance without any conscious awareness of the push against the ground. While the notion that this is achieved purely by a pull is as fanciful as the idea of lifting one by one’s own bootstraps, Pose does encourage a fairly efficient take-off with minimal conscious muscular effort. I was fascinated at Loughborough to see just how quickly jonp could get off stance. So despite rather questionable theoretical underpinning, in practice Pose works fairly well. Nonetheless, I am inclined to think that an elite athlete, especially a middle distance runner, would probably be well advised to work more explicitly on developing the strength and coordination to capture and release the maximum amount of elastic energy. I doubt if Pose drills augmented by hamstring exercises are adequate.
It might be that Pose enthusiasts will complain I have mis-represented the actions involved in the sequence pose, fall, pull. If so, I will gladly listen to their criticism and hope to improve my understanding. There is a certain mysticism in the way that Pose is described and in my attempt to provide a concise, concrete account I have omitted some of the subtleties. Nonetheless, I am quite confident that Dr Romanov’s exposition of the mechanism violates the laws of physics, as is illustrated both in the paper in Sports Biomechanics in 2007 and the paper presented at the ISBS conference in 2009.
Are there practical problems with Pose?
While I have little faith in the theory of Pose, that in itself would not necessarily undermine the practical utility of the Pose technique. After all, many of the images created in the Alexander technique such as imagining the neck extending or the back broadening have relatively little correspondence to what actually happens to the relevant part of the body during practice of the Alexander technique. Yet there is little doubt that Alexander technique promotes good posture. In many circumstances the image is more important than the precision of the anatomical description.
Unfortunately, I believe that Pose has not only theoretical problems but also some practical problems, most importantly in regard to foot dynamics. The most extensive scientific study of the effectiveness of Pose technique was the study performed in Tim Noakes laboratory in Capetown in 2002 and published in the Journal Medicine and Science in Sports and Exercise by Arendse and colleagues in 2004. The investigators examined the stresses acting at knee and ankle during Pose running compared with mid-foot running and heel striking. Dr Romanov was the coach who instructed the Pose runners, so we can assume that the teaching was in accord with Pose principles at the time. The measurements revealed less stress around the knee joint in the Pose runners – a credible and important finding which has been strongly proclaimed in subsequent literature promoting Pose. The study also showed that Pose was associated with greater stress around the ankle joint – a warning of risk of injury to Achilles tendon, calf muscles and plantar fascia, unless special precautions are taken. This adverse finding of the study has received much less prominent publicity in the Pose literature.
I suspect this problem arose because prior to the Arendse study, orthodox Pose teaching placed too much emphasis on maintaining the foot in plantar flexion while on stance. This potentially damaging foot posture is still shown in a very large number of the illustrations in the 2004 edition of the Pose Method of Running. That edition does at least acknowledge in the text that the heel might brush the ground, but the reasons for this are not discussed. I suspect that currently, many Pose coaches do adjust their teaching to minimize the risk of stress around the ankle, though I know from talking to beginner Pose runners that Achilles problems still occur, and I consider that Dr Romanov should have been more active in emphasizing the risks.
There is another topic that I have touched on indirectly above: the psychological effects, good and bad, about the way Pose is taught and marketed. In my next post I will discuss these, before returning to the topic which I regard as one of the most important aspects of running style: how to achieve a short time on stance while minimizing stress on muscles and joints. That topic will include a discussion of foot dynamics taking account of some of the recent studes that have compared shod and barefoot running.