Muscle Contractility part 1

Muscle Contractility

Part 1 – Introduction

In the article “Muscles Limit Performance” I built the case that your muscles are the primary determining factor in your running performance.  Since we have now established that fact, you are probably asking for more specifics.  What specifically about my muscles limits performance?  What is the best kind of training to conduct in order to improve my muscles?  These are the questions we will answer in this series.

Muscle contractility is the primary factor that limits performance.  Runners with superior muscle contractility outperform those with inferior contractility.  Muscle contractility is composed of three muscle characteristics –strength, speed of contraction, and resistance to fatigue.

The bad news is that muscle contractility is heavily influenced by genetics.  As much as 70 – 80 percent of improvements from training are controlled by genetics.  If you want to be a world class runner the first thing you have to do is choose the right parents.  No amount of training will overcome poor genetics.  The good news is that muscle contractility can be improved, oftentimes improved significantly, with training.  If you improve any of the three characteristics your performance will improve.

Before we delve into the specifics of the three characteristics, we need a working knowledge of the basics of muscle composition and function.

As you are probably aware, there are different types of muscle fibers.  We don’t really need to go into excruciating detail on all the different types and classifications though.  There are just a couple of important things to know about fiber types.  First, there are two basic classifications of muscle fiber types – slow twitch and fast twitch.  Second, there are large differences between these two fiber types.  Basically, fast twitch fibers are stronger and contract faster than slow twitch fibers.  Though they are slower and weaker than their fast twitch brothers, slow twitch fibers are significantly more fatigue resistant.

Unfortunately, the distribution of fibers is genetically determined at birth and probably doesn’t change with training.  If you were born with a preponderance of slow twitch fibers training won’t change those fibers into fast twitch fibers.

Not only do slow and fast fiber types exhibit different characteristics but the same fiber types possess different capabilities across individuals.  Grades of fastness or slowness vary in both slow and fast twitch fibers.  For example, physiologists believe that some runners’ slow twitch fibers can contract at nearly the speed of the average runner’s fast twitch fibers.  This hypothesis would explain how Alberto Salazar, who was tested to have 92% slow twitch fibers, until recently held the world 8k road record.  His slow twitch fibers were of the variety that contracted at the speed of the average person’s fast twitch fibers, enabling him to run very fast for long distances.

Whether slow or fast twitch, muscles fibers work the same way.  When a muscle fiber receives a command from the brain, that muscle fiber either fires or it doesn’t fire.  This is called the all-or-none principle.  Additionally, when a muscle fiber fires, it contracts with all its strength.  There is no range of effort for an individual muscle fiber.  It either contracts all out or not at all.

Obviously we don’t perform every activity with all our strength or at an all-out running pace.  Instead, your brain controls the overall strength and speed of movement by controlling the number of fibers it activates.  If additional strength or speed is required to perform an exercise, the brain recruits more slow and/or fast twitch fibers.  Additionally, fibers will contract as quickly as they are capable unless some external force slows them down.  That’s why we can’t move heavy weights as quickly as we move lighter weights.  The weights are heavy enough to slow down the speed of contraction.

Muscle fibers are activated by the brain as they are needed, starting with slow twitch fibers and then recruiting additional slow twitch and fast twitch fibers as needed.  The more fibers activated the faster and stronger the movement will be.

The previous paragraphs are extremely important and it is imperative that you understand them.  Here’s why.  Muscle contractility controls performance.  Contractility can only be improved with training.  The only way to train muscle fibers is by activating them and working them hard.  An untrained fiber will not improve.  Unfired fibers are untrained.  Your brain will activate only the minimum number of muscle fibers needed to meet the needs of a particular exercise.  If your exercise program doesn’t cause a muscle fiber to be activated, that inactive muscle fiber will not improve.

In order to improve your overall muscle contractility you have to train all the muscle fibers you are capable of activating.  That can only be accomplished by 1) making sure your exercise program is set up to in such as way that you activate most or all of your fibers and 2) that you train those fibers at close to their maximum capacity.  These facts must form the basis for any effective training program.

One last thing; now you know why easy runs don’t cause improvement.  They don’t train the few fibers they do activate hard enough to cause an improvement.


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