Friday, January 24, 2014

Let's talk about strength

I am going to write a couple of posts about strength, what is it, how to develop it and how to maintain it.

First of all, let's define what is strength in physic:

Strength = mass*acceleration

As we can see, strength is the product of two factors: mass and acceleration.
Moving from physic to physiologic, the mass (m) corresponds to the muscular cross-sectional area, roughly “how big the muscle is”, and the acceleration (a) corresponds to the nervous system (Kenney, Costill & Wilmore, 2011).

All clear so far?
Let's go a little bit deeper.

Our muscles are made of fibers and there are three kinds of them:
  • Type I
  • Type IIa
  • Type IIb

Type I are our "slow twitch" fibers, aka "red fibers" due to the elevated number of mitochondria that are located within them. This kind of fibers have a great endurance capacity and are the ones most developed in endurance sports.

Type IIa are kind of hybrid of Type I and Type IIb fibers. Their color is pinkish and they share the characteristics of both fibers. According the kind of training, your body is able to convert them in Type I or Type IIb.

Type IIb are our “fast twitch” fibers, aka “white fibers” due to the lack of mitochondria. They rely solely on the anaerobic system and they get fatigued very quickly. Yet, they are able to contract very rapidly and they are the main fiber developed in power and strength sports.

While I was training in the gym, I have been listening to a lot of people say stuffs like: “I gotta training this way 'cause my biceps are made of red fibers” and so on. Unless you put a needle in arm and you take a bit of your muscle to analyze it, it is impossible to know the percent of fibers composing your muscles. On the other hand, with proper training, is possible to “shape” the Type IIa; for instance, a 10000m runner is more likely to have more red fibers than an Olympic weight lifter due to the different kind of training that they follow. By the way, the number of slow and fast fibers it predetermined from the birth.

When we are talking about acceleration (a), we are considering the motor units and the central nervous system.

Motor units are composed of a the neuron and all the muscle fibers that it innervates. Each neuron innervates only one kind of fiber although it can innervated more than one fiber.

The central nervous system (CNS) is composed of the brain and the spine cord. The CNS govern the activation of the motor units.

(for all this session: Birch, MacLaren & George, 2005)

Ok, for today is enough.
In the next post I will cover in which ways the CNS can affect the strength output.


Birch,K., MacLaren, D. & George, K. (2005). Sport and Exercise Physiology. Oxford: BIOS Scientific

Kenney, W., Costill, D., & Wilmore, J. (2011). Physiology of Sport and Exercise. Leeds : Human Kinetics

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