It's a fiber thing.

Nurse: “Doctor: there’s an invisible man in the waiting room.”

Doctor: “Tell him I can’t see him.”

A recent study found that in exhumed cadavers, there were no type II muscle fibers.  The question asked is, where did they go?

In every person there are 2 broad types of muscle fibers: type I and type II.  There are several sub strata of type II but for our discussion let’s keep focused on these two types.   

 If you’ve ever had turkey on thanksgiving, you’d know them by another name: dark and light meat.  Dark meat is typically type II muscle fiber (short burst of energy muscle fiber) and light meat is usually type I (or endurance energy using muscle fiber). 

As you know, when you strength train you’re actually energy system training.   What, you say?  Energy system training?  You don’t know what that is, either?   Given what I see on the gym floor on a daily basis, I know that many people don’t know what this means because very few of us are actually making use of it in our workouts.

 Here are the three energy systems that a body uses to do work:   ATP-PC system, Anaerobic system, and Aerobic system.  At all times, all three energy systems are always working simultaneously.   Depending on the activity, one of the three systems gets focus. 

The ATP-PC energy system is used during short durations of work; say 10 seconds or less.

The Anaerobic system is typically focused on 2 minutes of effort or less.

The Aerobic system is used for activity lasting more than 2 minutes.

Here’s the idea. 

When you do short bursts of activity (for example strength training and sprinting) we focus on the ATP – PC energy system to do work.  This typically recruits the type II muscle fibers to do these high intensity short burst of energy.

When we use the anaerobic system, we shift focus from type II to type I as we near the 1 – 2 minute range of work time.    This could be longer sprinting (400 meters for example) or a timed strength set less than 2 minutes long. 

We kick the endurance work in when we go to 2 minutes or longer and typically this is distance running biking, swimming, or some other activity that lasts longer than 2 minutes.  This is usually a low intensity activity to kick in the type I fibers.

The problem here is usage.  Can you think of any other activities that last longer than 2 minutes?  I can.  Walking, sitting, driving, and practically any other number of activities that we do on a regular basis is a low level endurance activity.  We consistently use our type I muscle fibers all day long, every day.  Where do the type II muscle fibers go?  

Use it or lose it is a phrase I bet you’ve heard.  That’s exactly what happens.  They don’t get used and so the body adapts.  It stops focusing on them and they atrophy to the point of disappearance. 

Forgetting for a second that a person’s genetics determine their makeup of type I and type II muscle fibers, we can influence whatever types we do have.  But you may be asking me, why should I care about type II fibers?  Who cares?

I’ll tell you why you should care.  I heard this story about a trainers 80 year old client.  Firstly, congrats being 80 years old and working out.  But here’s where we can care about muscle fiber recruitment:  during a walk a gust of wind blew and her hat picked up off her head.  Like anyone, she quickly reached to grab the hat but in doing so injured her shoulder because she was moving too quickly!  Yikes!

What can we do?  Genuine strength training, I argue.  Now we don’t teach a client who has never run in their life, to run by making them run a marathon.   Nope.  We start off with significantly shorter distances and intensities.  The same is true for strength training.  Safely progressing someone at lower intensities (in the 15 to 20 rep range) will help to build strength so that they build not only strength but skill (i.e.: compound movements like a squat).  Building that skill is usually dependent on what the client wants to achieve and what their current fitness level allows.  Ask a professional if you have any questions.   

Let’s bring type II muscle fibers back by learning to progress into explosive activities that promote short duration work.  The fitness industry is full of endurance activity.  Let’s work on the short duration, high intensity energy systems too. 

Mo-tate.  Motivate your life to motion.