Wednesday, June 24, 2009

Plastic vs Elastic when talking about Human Perfomance

The body is often variously described as plastic and/or elastic. Sometimes it seems the terms are used interchangeably. But what do they mean - at least in terms of the body? The are complementary. Elastic: to stretch away from a shape but be able to return to the original form. Plastic: to stretch out (or not) to a new form, and be able to maintain that new form, way, approach. How these concepts apply to the body have inspired some compelling models in human performance training.

Elastic is the more common term. Elastic bands: they stretch out; the snap back. That ability to expand and have the object return to its original state is the biggie part of elastic.

Elastic also has this interesting property with energy. For example, pulling back a bow string loads the bow with the energy to drive the arrow. When the bow string is released, the bow springs back to its "relaxed" position. Entropy is achieved once more.

Muscles are often described as "elastic:" they stretch out; they snap back.

Depth Jump - stretch shortening
Muscles also takes advantage of elastic energy, in particular stored elastic energy. Elastic energy is a big part of plyometrics. For instance "depth jumps." A person wants to leap up in the air. So before they do this, they stand on a box about a foot off the ground, jump down and then quickly leap straight up. That jump will be higher than if they just leapt up from a standing position. Why?

Well the theory goes (and it's been tested a lot), that pre-stretching a muscle (eccentric contraction) stores up energy in the muscles and tendons that if translated very quickly from storage to use (the brief transition between storing to using, called amortization), that energy can be used by the muscles as a kind of power assist.

The difference between muscles and a bow string is that the bow string can maintain that stored energy longer than our muscles. Stored elastic energy in muscles translates very quickly into heat if it's not used immediately by the muscles for work.

This is also in part why plyometrics is about very quick movements: translate the stored energy into work before it dissipates into heat.

an aside - what don't stretch

Since elasticity is related to stretching, a note about what does stretch and what doesn't. Generally speaking, muscle and skin stretch. Tendons, the bits that join most muscle to bone, don't stretch. But for a few types, ligaments, the bits that connect up joints, don't stretch either. Fascinating, eh? And here's another bit: tendons carry electricity to the muscle; ligaments are without charge.

Plastic - constant adaptation

Elastic is about being pulled from an original state and returning to its original state. Plastic is the complement of this about being able to be pulled from an original state into a new state and then staying in that new state.

Despite its relatively recent use to describe a material, plastic as a concept is rather old. According to an online etymology, it's been used in English (1632) to refer to something "capable of being molded" and 1839 - surgically - talking about "fixing a deficiency of structure," and finally 1905 as a "solid substance that can be molded."

When folks talk about the body as plastic, they're also talking about this ability to be reshaped. Scientists have studied this reshaping for some time. There's Wolff's law, which considers how bone is constantly remodeling based on use - or lack of use. Then there's Davis's law which talks about soft tissue remodeling, similar to Wolff's on bone remodeling. And these both can be seen to act along the lines of the SAID principle: specific adaptation to imposed demand
(aside: just try to find the history of this term - everyone talks about it, but the source? i'm sorry i haven't found who first started talking about it, but with Wolff and Davis, it's easy to support it; that said the principle of specificity (seemingly used interchangeably with SAID) is similar but perhaps different in intent, suggesting that training should be similar to the action to be performed. Anyway).

Only more recently though has research begin to show that our brains and nervous system remain plastic. It used to be thought that after infancy, our brains effectively set. Work since the last part of the 20th century, discussed in the Brain the Changes Itself, shows that this is not the case. Our nerves and brains, too, re-pattern based on demand.

This patterning is refered to as neuroplasticity. If a limb is injured, a nerve cut, it rewires to utilize other nerves available. Likewise if the brain has an issue, it's been found that with work, it will rewire itself to use another part of it to make up the difference.

This knowledge of neuroplasticity, of brain and nerves rewiring, has made it possible to develop new practices to address challenges from stroke recovery to reducing the effects of dyslexia to autism. Some of this work has been put into research-tested products like those by Posit Science to help older folks especially recover brain function. I've been watching some of my elders benefit hugely from "playing" with these brain practices to help retune the brain to a sharper form that can attend, focus, hear better.

Plastic and Elastic: Always On, All the Time
Organic life is pretty amazing. We as such are also pretty amazing: bio-mechanical, electro-chemical, neurological beings. We stretch out and snap back; we also adapt. All the time. Not just in shape but in practice, learning.

A profound challenge in research seems to be how we can best design training to enhance best adaptations for best performance.

One of the attractions of Z-Health, at least to me, is that it takes advantage of the elastic and the plastic, using the plastic to enhance the elastic (as per this discussion of form and efficiency in the front squat). It works with the SAID principle, neuromechanically.

Z-Health extends the SAID principle to suggest that we are always adapting, always and exactly to what we do, and rather immediately. Therefore what we practice is what we become (we are what we eat?). Practice the most efficient neural patterns for plastic adaptation; enhance elastic performance. The intriguing thing is just how immediately these adaptations do take place.

This all started as a discussion of plastic and elastic. While elastic is so well known and used in muscular training, it's perhaps the research in plasticity that will be the new plyometrics in sports and well-being training.


Rannoch Donald said...


IO hope you get as much from writing this stuff as I do reading it. thanks once again for making me stop and think.

Insightful as always.

Anonymous said...

I think the new book, "Move into Life" by Anat Baniel talks about this concept as well.

Nice blog - very interesting stuff.


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