A Puzzle and a Tribute

The puzzle

The proposed third section of my series on Dancing with the Devil will deal with the mental state necessary to allow us to achieve the movements required by the principles of biomechanics to achieve efficient running – the psychodynamics of running. However, I am delaying tackling the psychodynamics because there is one large question of the biomechanics of running that still puzzles me. The problem is deciding on the most efficient muscle action to achieve an adequately long stride when running at fairly high speed.

Evidence strongly suggests that once cadence reaches 200 steps per minutes, further increases in cadence would require a rate of muscle contraction that becomes increasingly inefficient. Therefore, efficient increase in speed required an increase in stride length. A longer stride length at fixed cadence requires a faster average speed of the leg as it moves forwards from stance to stance to support the body, because the distance from footfall to footfall is greater but the duration of the stride is unchanged.

One way to achieve a higher average speed of the leg is to use more vigorous hip flexion in early swing. However, this action will tend to bring the foot forwards rather than upwards at lift-off, resulting in the foot being carried at the end of a longer lever arm In contrast, if lift-off is largely via hamstring contraction with minimal hip flexion, the knee flexes more, the foot rises behind the line for point of lift-off to hip, the lever arm is shorter, and hence the leg naturally swings faster under the influence of gravity while the other leg is on stance.

In fact the swing is a power assisted pendulum rather than a simple pendulum driven by gravity. To the extent that we use muscle power rather than gravity to drive the swing, it makes sense to drive the foot along the shortest path from lift-off to foot fall. The shortest trajectory is a low arch in which the highest point of the foot trajectory is achieved at approximately mid-swing, rather than the pear-shaped trajectory that includes the initial high upward loop to a position behind the buttocks.

So to resolve the issue, we need either a complex mechanical model which is impractical, or alternatively, we need to examine the evidence from observation of elite runners. Many elite runners, such as Haile Gebrselassie, do lift the heel quite high behind the buttocks, so that the foot trajectory is not a simple symmetrical curve, but it does nonetheless appear that the foot is pulled forwards at lift off as well as upwards. So the answer appears to be a compromise.

While I have a fairly clear mental image that promotes a strong hamstring contraction and a different mental image that promotes hip flexion, I have not yet been able to decide on the mental image that promotes the optimum compromise. So for the immediate future, I am postponing part three of ‘’Dancing with the Devil’ until I have had a greater opportunity to try different mental images.

The tribute

The tribute is to the ‘Efficient Running’ thread on the Fetcheveryone website (http://www.fetcheveryone.com ). This thread was started on 20th August 2007 with a question about heel striking, and reached its 10,000th entry a few days ago. That reflects an average of about 50 entries a day, so keeping up with the torrent of material has been enough to leave one breathless, or maybe just sleepless. The entries have included many thought provoking ideas about efficient running, in addition to much social chit-chat.

At times people have complained that very little is ever decided on the thread because too many individuals are fixed in their thinking and unprepared to change. My own view is that most people hold fairly strong opinions largely because a particular way of running ‘feels right’ and/or is based on concepts which appear to make a great deal of sense: concepts such as the notion that it is best to land with the foot under the centre of gravity (COG). This seems to make sense because it minimizes the inevitable braking effect when the point of support is in front of the COG. However, as discussed previously in this blog, unless the foot lands in front of the COG, the body must continually accelerate or suffer a face down crash after a few strides. It is impossible to land under the COG when running at constant speed on a level surface in the absence of wind resistance

Despite some skepticism regarding the laws of physics, illustrated by the statement of one Pose coach that arguments based on physics ‘matter diddly squat’, the discussions on the thread have often sparkled and have challenged me to examine carefully what I am doing when I run, and also to think deeply about biomechanics. I hope this has led to some useful conclusions.

Looking back, I think that the Fetcheveryone thread has been the second strongest influence (after Gordon Pirie’s book ‘Running Fast and Injury Free’) on my thinking about efficient running. The scene was set by an entry by Cabletow, posted 5 hours after the initiation of the thread, which provided a succinct summary of the five principles espoused by modern schools of thought about efficient running. In his words, the principles are:

‘increase cadence to 90 per leg
Land under your cog with a bent knee to release plyometric energy
Land with a rearward moving foot and relaxed ankle
Do not push off but lean forward into the run
Limit arm movement, bend the elbows and do not reach too far forward.’

These principles have exerted a huge influence on much of the discussion on the thread. I think they are excellent principles, though I would take issue with two features. As already discussed, landing under the COG is impossible when running at constant velocity on a level surface in the absence of wind resistance. The other issue is the recommendation to lean forward. This is a confusing and sometimes confused issue. At times, people take it to mean a forward inclination of the long axis that passes through point of support, hips and shoulders at mid-stance, as illustrated in the spectacular picture of a muscular young man running on a beach in the PoseTech advertising literature. At other times, as emphasized by Cabletow himself in recent posts, it is taken to mean the forward lean of the line from point of support to COG that occurs as a result of hip extension in the second half of stance.

Both forms of lean result in a gravitational torque that tend to rotate the body in a face forwards and downwards direction. More confusing is the notion that lean promotes forward propulsion by means of this gravitational torque. This is a concept that arises from the questionable biomechanics proposed by Dr Nicholas Romanov in the theoretical underpinning of the Pose Method. It is a concept that ignores the law of conservation of angular momentum. If a face forwards and downwards torque is applied at some point in the gait cycle, it must be counteracted by an oppositely directed torque at some other point in the gait cycle if a face down crash is to be avoided. Nonetheless, the concept that gravitational torque provides useful forward propulsion continues to exert a strong influence on the discussions on the Fetcheveryone thread.

In relation to my personal priorities, the main limitation of the five principles proposed by Cabletow are that they do not adequately address the question of how to run with maximal mechanical efficiency, in the sense of using the minimum amount of energy per unit distance at a fixed speed. The five principles encourage a safe running style that minimises risk of injury. Minimising risk of injury is crucial to promoting good performance, but it leaves unanswered the question of the most efficient way to get the legs forward quickly enough to allow running at a constant high speed.

In my opinion, three of the modern schools of efficient running do make a coherent attempt to address the issue of how to run efficiently at high speed. These are Evolution Running developed by Ken Mierke (http://www.evolutionrunning.com); Stride Mechanics developed by Jack Cady (http://www.stridemechanics.com ); and the BK method developed by Frans Bosch and Ronald Klomp (http://www.runningdvd.com/content/en/). The concepts of Stride Mechanics have been presented occasionally on the Fetcheveryone thread by Jack Cady himself. However, as far as I can discern, neither Evolution Running nor BK method have been presented so far by individuals who are experts in those schools of efficient running, and I hope that they might be at some time in the future.

This tribute has not been a eulogy to a departed friend, but an account that reflects my own personal priorities, and includes an expression for hope for a broader perspective in the future. The Fetcheveryone Efficient Running thread has been a major source of inspiration to me. Thank-you to all who have contributed.

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2 Responses to “A Puzzle and a Tribute”

  1. Simon Says:

    Canute,

    Good stuff, thought provoking and well though out as usual – I’ve been reading through each of the ‘putting the steps together’ sections and have a few thoughts:

    Torso

    I agree with the upright torso with a lean being needed for change of pace and for uphill running or running into a strong headwind. My personal view of the lean is that it changes the relative position of mid-stance and so effects the balance of horizontal braking and acceleration either side of mid-stance. So a forward lean effectively shifts mid-stance back a little so producing less braking and more accelerating horizontal forces.

    Arms

    Most people find an arm focus easier, but for those that can successfully develop perception of the legs they can get a more holistic feeling to running where everything is moving together – I believe that to be the very best perception but it takes a lot of effort to achieve.

    Long axis rotation

    Seems to have a very low energy cost and a small benefit in extending stride length. Over rotation will misallign limbs though. I think the rotation should be allowed to happen but not overly encouraged.

    Swing phase

    The eccentric loading of the hip flexor coupled with a hamstring contraction and release of muscular elasticity in the achilies/calf all conspire at terminal stance to prevent the leg from being left behind. If the leg is left behind due to late intervention, the requirement for acceleration and later deceleration will be even greater. A certain amount of forward acceleration and later deceleration seems unavoidable, but luckily each part of the change in speed can make use of eccentric loading followed by concentric contraction and release to make efficient movement. I think this is glossed over somewhat in Pose because of the potential for harmful perceptions to generate an overstride and/or a badly formed landing.

    Regarding the puzzle mentioned above, I think the key lies in the well timed use of the hip flexor plus a precise hamstring contraction that is not overly strong. The hamstring contraction needs to be just enough to prevent the knee from fully extending and enough to allow momentum to continue to flex the knee (release of muscular elasticity in the calf and achilies causes an upwards impulse that will flex the knee). Once the hip flexors move the upper leg forward, the lower leg will tend to undergo a further acceleration in a ‘whip-lash’ manner that will complete the shortening of the leg making the forward drive easier.

  2. canute1 Says:

    Simon,
    Thanks for your thoughts. Overall we are in close agreement. Here are my thoughts in response to thoughts

    Torso: Yes, the forward lean effectively shifts mid-stance back a little (if we assume that midstance is when point of support, COG and shoulder are aligned). When leaning the acceleration due to a backward component of the push on the ground (generating forward GRF) begins even before midstance. However, at constant velocity in absence of wind resistance, the acceleration must be balanced by braking so we must spend less time on the ground after mid-stance than before, and there will be less hip extension at lift-off. This results in less pre-loading of hip flexors. So on balance, it appears than lean is only useful when we need to accelerate, or overcome wind resistance.

    Arms: When I get to the section on psychological factors I will discuss arms some more, but I am interested in your proposal that focus on perception of the legs gives a more holistic feeling. In fact, in the psychology section, I will discuss focussing on ‘the whole image.’

    Long axis rotation: I suspect you are right that it should not be overly encouraged. I would be interested to hear the comments of a Chi runner on how conscious the rotation should be.

    Swing phase: Thanks for your thoughts on the ‘puzzle’. The whip lash following release of load on the calf sounds plausible, and should achieve the desired shortening of the lever.

    Canute

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