A reply I made on Bearpowered last week about why I feel enhancing fiber length should be one of the main focuses in our pursuit of faster running:

The reason longer fibers cause a faster contraction is basic geometry, see the following:

Sprint performance is related to muscle fascicle length in male 100-m sprinters.

https://jap.physiology.org/content/88/3/811.full

“Differences in maximal shortening velocity between muscles were determined, to a much greater extent, by differences in muscle fiber length rather than by biochemical differences (11, 27).”

AKA maximal shortening velocity is determine to a much greater extent by muscle fiber length than it is by fiber type proportions(% fast twitch).

Then check out this diagram to see how a longer fascicle creates a greater shortening velocity: https://jap.physiology.org/content/88/3/811/F3.expansion.html

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Relationship between sprint performance and muscle fascicle length in female sprinters.

https://www.ncbi.nlm.nih.gov/pubmed/11385937

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Fascicle length of leg muscles is greater in sprinters than distance runners.

https://www.ncbi.nlm.nih.gov/pubmed/10862540

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Then there are plenty of studies showing fascicle/fiber length can easily be increased by eccentric training, sprint-jump training (plyometrics), ballistic resistance training, basically anything quick and explosive, utilsing the stretch-reflex is best. Even chronic stretching protocols have been shown to greatly increase fiber length.

Effects of dynamic resistance training on fascicle length

and isometric strength

https://investigacion.uclm.es/documentos/fi_1166966171-Alegre_LR_501-508.pdf

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Acute and chronic effects of passive stretching on voluntary and evoked muscle force, the length-tension relationship, ankle joint range of motion, and musculotendinous stiffness in the plantar flexors

https://gradworks.umi.com/33/52/3352823.html

This one is only a dissertation, but again the postulation is that chronic stretch may stimulate longitudinal hypertrophy (fiber lengthening).

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This one is very important to read. Look at the section on Eccentric Training especially:

The Use of Eccentric Strength Training to Enhance Maximal Muscle

Strength, Explosive Force (RDF) and Muscular Power – Consequences for

Athletic Performance

https://www.benthamscience.com/open/tossj/articles/V003/52TOSSJ.pdf

“Animal experiments have shown that eccentric resistance

training, especially when performed at long fiber lengths (i.e.

at highly flexed joint positions, such as in deep squats) may

lead to sarcomere addition and elongated muscle fiber

lengths [29-32]. Notably, elongated muscle fiber lengths will

contribute substantially to the gain in maximal muscle power

induced by training. Thus, simulation analysis using empirical F-V and P-V relationships obtained for single human

muscle fibers reveals that a 10% increase in maximal isometric muscle fiber force leads to a 10% gain in maximum

(peak) power production, while a 10% increase in fiber

length with a corresponding increase in maximal fiber shortening speed (Vo) cause maximum (peak) power to also increase by 10%. However, the relative gain in muscle power

generated at high contraction speed (corresponding to 75%

of Vo) is 4-fold higher (42% vs 10%) when comparing the

effect of increasing muscle fiber length by 10% vs increasing

maximum isometric force by 10%, respectively. Most

potently, however, if a 10% gain is achieved both for maximum force and muscle fiber length, respectively, this yields

a 56% gain in high-speed power (at 75% Vo). In comparison, maximum (peak) power production is increased by

21%. Thus, any training induced increase in muscle fiber

length is likely to have a strong positive influence on the

magnitude of maximal muscle power production, especially

during very fast movements.”

It doesn’t need to be said that this is very exciting information indeed. I hope you all static/pnf stretch before and after your workouts 😉 .

There are other studies pointing to the idea that arginine (or aakg) supplementation may enhance the fiber lengthening process, and thus it would be wise to supplement with that too while training for longer fibers. Generating high levels of relative force is still a huge focus, yet to me, this, fiber lengthening should be an even bigger one, since it is ignored by almost everyone (amazing how people miss things that were right under their noses).