Training from Scratch (IV): Stability (2)

‘Functional’ exercise pays lip service to biomechanics but forgets about mechanical stability, and that’s too bad because you can’t spell ‘biomechanics’ without ‘mechanics’.

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You can’t spell ‘biomechanics’ without ‘mechanics’

The engineering concept of mechanical stability, which I’ll refer to as stability2, was imported into biomechanics in the late 1980s.

The importer, Anders Bergmark, belonged at the time to the Department of Solid Mechanics at the Lund Institute of Technology (Lunds Tekniska Högskola, or LTH). In 1989, he published a thesis titled Stability of the lumbar spine: A Study in Mechanical Engineering.[1]

The subtitle is a dead giveaway of Bergmark’s intention: address the lumbar spine as a mechanical system.

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A thought experiment

The spinal system must be mechanically stable in essentially the same way as purely passive engineering structures […] namely by possessing stiffnesses that are high enough.
Anders Bergmark, The Stability of the Lumbar Spine, p.5

Bergmark’s hypothesis is that mechanical stiffness contributes to the support system of the spine. Bergmark illustrates how muscle stiffnesses do the stability2 job with a thought experiment (didn’t I mention that they were useful in science?): a T-structure with a weight and a spring attached to it that stands vertically on a base when the force of the spring matches the pull of the weight (see below, reproduced from Bergmark 1989:25)

In both A and B, the T is standing because the potential energy of the spring (P) and of the weight (Q) cancel one another. But the spring in structure A is stiffer than the spring in B: it has a higher (potential) energy P than the spring in the structure B and thus could compensate for forces that would act in the same direction as Q.

The next stage of Bergmark’s thought experiment is to introduce a small disturbance in the system that adds up to Q (“a clockwise angular deviation Δφ”, depicted below), such that the potential energy of spring A could compensate for it, but not the potential energy of spring B. Explicitly, if the disturbance happened, the potential energy of both springs A and B would be converted in actual kinetic energy, but only spring A would pull the T back in place: with spring B, the T would still be slanted (clockwise).

nullThe force Q tries to increase the disturbance angle Δφ, whereas the force P in the spring tries to move the system back to the equilibrium position Δφ = 0. Thus the question about stability and instability is reduced to the question about which one, P or Q, that wins.
Anders Bergmark, The Stability of the Lumbar Spine, p.25

So far, Bergmark’s thought experiment illustrates that both A and B are in equilibrium but only A is in stable2 equilibrium while B is in unstable2 equilibrium. In other words, that A is mechanically stable on it own, while B could only be made stable through non-mechanical control (a tightening of the screw).

And now for the last step of the thought experiment: substituting the spring with a muscle and identifying muscle stiffness with “passive stretching and spinal reflex tension modification” (Bergmark 1989:26). Passive stretching increases the potential energy stored in the muscle and is purely mechanical. The “spinal reflex” is the Liddell-Sherrington Reflex, or stretch reflex, and does not require CNS control. As such, it is not considered to be “active” (the equivalent of CNS control is tightening the screw by hand).

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The successive editions of McGill’s Low Back Disorders (2002, 2007, 2016) offer multiple examples of lingering misunderstandings in clinical and performance circles, and of their consequences, but I picked just one illustration of the confusion between stability1 and stability2 (p. 158).

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Conclusion: Let’s build a brick shithouse

The taxonomy of stability1, stability2 and balance matters for science, but what about you?

Well, I said at the beginning that with stability2, gentleness would be out of the window, but I also promised to be constructive, so I kinda got myself in a box. But I can let someone else put the final nail in the coffin of ‘functional’ training (and trainers) and their ‘stability’ stuff:

Of course, De Franco sells books, DVDs, programs, supplements, etc., so bullshitting might be in his interest and on his agenda. But I’m not overly familiar with the rest of his work, so I’ll just assume that he’s not as full of shit dishonest, ignorant, or both, as others.

Again, I promised to be constructive so I won’t name the others. Or their publishing houses. (But one of them rhymes with “Dumbledore”.)

Back to De Franco’s argument then. It builds on the notion that, for athletic performance, ‘functionality’ is specificity. I made the same point in part (III), only more pedantically, but there was a point to the pedantry: extending the argument to activities of daily life (ADLs) is tricky. There’s case to be made that this trickiness caused the otherwise sensible idea of ‘functional training for ADLs’ to become what some philosophers of science would call a ‘degenerated research program’. Or a degenerated exercise program, if you will.

I’ll make that case in a scholarly article, one day, but for today, I’ll jump to the culprit: ‘functional training’ degenerated because stability1 was considered the paradigmatic function for ADLs. Now, if you substitute stability1 with stability2 as the paradigmatic function for ADLs, ‘functional’ training for ADLs collapses on athletic training, give or take.

  • ‘Give’: De Franco’s argument for loaded carries, which develop strength, endurance, stability{1,2} and athleticism (however it’s interpreted).
  • ‘Take’: athletic excellence is often at the expense of health markers (strength athletes compromise cardiovascular fitness, endurance athletes are vulnerable to sarcopenia).

With this remark, we reach a turning point: the foundations for ‘training from scratch’ are laid down, and all that’s left is wrapping up everything in a nice ‘functional’ system that can take fitness goals as input and spit out a program that would make anyone who follows it as stable as a brick shithouse.

And that’s what I’ll do in the next part. No less.

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Notes

[*] This is a theoretical maximum under the assumption that each word carries marginal information. The actual information content may, in fact, be lower.

[1]^All quotes are from Bergmark’s introduction. The complete reference is: Anders Bergmark (1989) Stability of the lumbar spine, Acta Orthopaedica Scandinavica, 60: sup. 230, 1-54, DOI: 10.3109/17453678909154177.

[4]^ McGill, Stuart M & Marshall, Leigh W (2012), Kettlebell Swing, Snatch, and Bottoms-Up Carry: Back and Hip Muscle Activation, Motion, and Low Back Loads, The Journal of Strength & Conditioning Research, 26 (1): pp. 16-27, doi: 10.1519/JSC.0b013e31823a4063. Conclusions about total spinal load and spine stiffness are based on the combination of actual measures (“all muscles except the LEO [Left External Oblique] increased their activation with the bottoms-up carry”, p. 24) and theoretical arguments (“the sum of the muscle activities will probably be important in terms of total load on the spine and in terms of spine stiffness (not quantified in this study)”, ibid.), while joint compression and shear loads were measured and found “significantly greater in the bottoms-up position compared with that in the racked position.” (ibid.)

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