Thursday, March 14, 2013

A Primer on Size, Strength, and Skill

Let me begin this article with a quick apology about the gap between this article and the last few.  I have a good reason - my daughter being born!  While this has easily been the happiest time of my entire life, it's also been one of the busiest.  Hopefully now that we're all settling into a bit more of a routine, I'll be able to get back to it.

Anyway, there's a few articles I'll be posting soon that shed light on what exactly drives hypertrophy, strength, where they overlap, and where they differ.  The ultimate goal of these articles is to discuss how we can optimally train these two components of fitness.  These topics do require a cursory understanding of muscle physiology to be useful, so let's start with the basics.

Your Body, the Electrician
Imagine your bicep muscle as thousands of little electric winches all strung together in parallel.  These winches, which represent individual muscle fibers (NOT your entire "muscle", but the individual strands that make up a muscle) can only pull or release, which is to say that they can only create tension by pulling inwards.

To operate a winch, you need to have power, which is where your motor neurons come in.  Motor neurons are essentially power cables that power a group of winches.  Generally speaking, the finer the muscle movement must be, the closer the ratio of winches to cables.  The very small muscles that direct eye movement have a much higher ratio of winches to cables, where a larger muscle responsible for gross movement pattern have a much lower ratio.  In either case, one single cable (nerve) and all the winches (fibers) that it powers (innervates) is called a motor unit.  

Its important to understand that a single fiber contracts at a variable frequency, but is ultimately either flexing or relaxing.  A muscle can and does have varying intensity of contraction and force production, but a single muscle fiber is binarily on or off.  Each contraction of an individual muscle fiber is known as a twitch.

The Contraction
The force of a muscle contraction can be modulated in a few different ways.  The nervous system can call on a higher percentage of available motor units, recruiting more fibers which participate and add to overall force production.  This is known as recruitment, or the amount of cables sending power to each group of winches.

Secondly, the nervous system can stimulate each motor unit with a stronger or higher frequency signal, causing each fiber to twitch more frequently.  This is can be thought of as an individual cable sending more power to each group of winches so that they pull and release at a faster rate.

Ultimately, a muscle can increase force production by altering how many winches are used at one time, as well as how frequently the winches are pulling and releasing.  

There's a lot more to it, but this is enough for now.

Differentiating Strength, Size, and Skill
All other variables held equal, a larger muscle will produce more force than a smaller muscle.  This is generally due to the increase in contractile proteins within the fiber, which can be thought of as increasing the amount of winches.  The bottom line is that force production is influenced by the cross-sectional diameter of a muscle.  Simply put, bigger muscles equal a stronger contraction.

In contrast, a muscle can produce more force through improvements in neural efficiency.  More motor units can be utilized, fiber recruitment increases, transmission speed increases, and force production improves.  It must be understood that the nervous system will only allow a contraction that it deems is safe.  Just as a stretching program signals the body that it's safe to increase ROM over time,  a strength training program conditions the nervous system that it won't rip your muscle off its attachment site if it allows you to use a higher percentage of your maximal strength.

These are the two primary adaptations to strength training.  The body also makes improvements in fuel delivery - intramuscular capillary concentration increases, glycogen (sugar) storage and fuel oxidation improves, and so on.

The last factor I want to mention is improvement to motor pattern efficiency, an often unspoken but very important topic.  In the context of strength training, this is the strength-skill connection.  In reality, it's the improvement of any skill as a result of getting better at the skill itself, not from any improvement in a physical attribute.  This phenomenon accounts for a much larger portion of gains than most trainees ever realize.  The bottom line is that strength is a skill; squat 5x a week and you'll get exceptional at squatting, but you won't be exceptional at even quite similar skills.  An 8 week squat program that yields a 15% increase in squat performance does not confer anywhere near a 15% increase in pure strength.  Much of that 15% comes from improvements in the skill of squatting. 

Motor pattern adaptation is more specific than we in the fitness world would like to think it is, but it's a readily observable occurrence.  Throw an untrained individual in a pool seven days a week and have them only breaststroke - that person would get somewhat faster at all swimming strokes and become a slightly better all around "swimmer", but would make far and away the most dramatic progress in solely the breaststroke.  Even more so, those general improvements would taper off severely once the person has a few months of training under their belt.  Generally speaking, the more the individual progresses, the less "global" their training benefits become. 

For now, it's enough to understand that when you get in the weight room and train, you get stronger, but you also get good specifically at whatever lifts you are performing.  This increase in skill accounts for a difficult to quantify but very significant portion of your gains.  The more advanced you become, the less general strength and size you gain.

Future Topics
We use the word "gains" loosely.  It should be obvious by this point that no training program can maximize gains in hypertrophy, neural efficiency, and strength-skill efficiency.  In the next article(s), we'll dive into how the body responds to various training protocols, and what you're really getting out of different types of training. 

The science might surprise you.  Some of it surprised the hell out of me.