Recruitment Part I – What Is It?

“Strengthening your core” is quite a common movement practice.

I wrote previously about a problem when using voluntary exercises to improve postural core strength. You are not hard-wired to work this way. The ability is there as a backup. You could say it is a secondary or redundant system – meaning it’s there, it works, but your primary design for strengthening your core is quite different.

More efficient and pleasant to use. But takes longer to understand - 7 years is my estimated training period.

FIRST, Let’s talk about redundancies. What is a redundant system?

Redundancies are backup systems we have when the primary method fails. For example, we have two functionally distinct brain hemispheres, two sets of limbs, two kidneys, two eyes and two ears - you find many instances when you reflect upon this. One of the amazing things about us is the sheer number of binary redundancies built into our biology.

We make the 1960s moon-shot look like a picnic.

Our movement system is organised in this same binary way.

You have a:

1. VMS - Voluntary Movement System for learning and controlling motor activities;

2. PSS - Postural Support System for maintaining balance during motor activities.

Together, these two movement systems operate as a whole to guide your muscular activities within gravitational forces on Earth. Understand that both systems have control over the exact same muscles, it all depends upon Recruitment. Recruitment is the process of selecting individual muscle fibres (cells) TYPES to do the work. Which is the best muscle fibre TYPE to use at any one micro-second of time?

So…

SECOND, Let’s talk about muscle fibres TYPES

This binary design continues into the design of muscle fibres (cells). Since the 19th century, it was thought that we have two TYPES of skeletal muscle fibre:

TYPE I: slow-twitch 'red' muscle fibres which are aerobic and resist fatigue;
TYPE II: fast-twitch 'white' muscle fibres, which are anaerobic and fatigue quickly.

Every voluntary muscle in our body was found to contain both TYPES.

However, from the 1960s, research started to reveal a new category of fibre that is transitional. i.e. it is a fast-twitching power delivering fibre that reconstitutes itself as a fatigue-resisting stamina type fibre when need dictates. This discovery caused a minor sensation in Olympic sports. One of the researchers had to redact portions of his scientific paper lest athletes use his discoveries to chemically bias their muscle mass to overcome training limitations.*

The situation grew even more complex - with these three fibre types being further divided into subtypes. However, we can still say today that muscle fibre structure is the expression of two distinct physiological parameters: resistance to fatigue and speed of contraction, with three distinct types existing along a spectrum between these two endpoints.

Do you notice any similarities between the two functional types of muscle fibres and the two functional types of movement systems?

Remember, BOTH SYSTEMS have control over EVERY MUSCLE. Who wins that war?

Dynamic postural balance (PSS) requires ongoing TYPE I contraction - the ability to avoid fatigue is particularly useful. However, voluntary motor activities (VMS) often require TYPE II speed/power – the ability to generate fast, powerful movements is also useful, even though these fibres fatigue quickly.

How do these two systems cooperate in selecting muscle fibre TYPES?

“Recruitment” describes the process of VMS & PSS choosing the fibre TYPES best suited for the current movement. Both VMS and PSS have rights over every muscle fibre - both can call upon muscles in different ways…

As it turns out - it’s a bit of a competition between VMS & PSS!!!

And it doesn’t always turn out well for us….