What Muscles Control How Fast You Run?

We all know that our muscles are responsible for moving our body. But it is the make up of those muscles and how they function that determine how fast we run.

What Are Muscles Really

A muscle – like your bicep, quadriceps or calf muscle – is really made up of a large number of muscle fibers. These fibers respond to motor units which are controlled by the brain. So when you do physical work, the brain sends a signal to the motor unit which then causes the fibers to contract or relax.

Those muscle fibers are also different, being made up of slow twitch and fast twitch fibers. As the name suggests, slow twitch fibers move slowly and fast twitch fibers respond quickly. There are actually 2 different type of fast twitch fibers – A & B – and the B fibers respond twice as quickly as the A.

The Task Makes a Difference

Muscles are made up of bundles of muscle fibers. Each muscle fiber acts as an individual unit and either contracts fully or not at all when called upon.

If you do something easy, like lifting a pen, your brain will recruit a small number of muscle fibers to do the work. The remaining muscle fibers aren’t required and so remain relaxed.

On the other hand, if you are weight lifting a heavier load than you ever have before, your brain will engage every muscle fiber.

Now if you’re walking, your brain will engage the motor units to fire predominantly slow-twitch fibers. Since there is no speed required, there is no need to fire those fast-twitch fibers.

On the other hand, if you’re running, more fast twitch fibers will be called upon to do the work. Now as runners, we know that there is ‘running’ and then there is ‘running fast.’ As you move from aerobic running – the type you can do for hours and hours – to anaerobic running – like sprinting or speed intervals – your brain will engage more fast twitch fibers through their motor units.

If you were to compare 3 groups of individuals and their prominent muscle fibers, you might expect to find the following:

  • Couch Potatoes: Predominantly slow twitch fibers
  • Endurance Runners: Lots of Slow Twitch fibers and Type A fast twitch fibers
  • Sprint Distance Runners: Lots of Type B and A fast twitch fibers

So That’s All Very Interesting. What Can I Do About It?

That’s a very good question. You see a lot of what determines our muscle fiber make-up is genetic. Yes, you were born with a certain set of muscle fibers and – to a certain extent – you are stuck with them.

BUT, the good news is that – if you want to run faster, or longer, or both – you can influence your ratio of fast to slow twitch muscle fibers. A pair of Canadian research scientists have estimated that 45% of muscle fiber make-up is determined by genetics while around 40% is due to environmental factors.

In other words, you have influence over 40% of your muscle fiber make-up. The way that you can get faster is by training faster and engaging in those activities that cause your brain and motor units to call on fast twitch fibers.

You see, if you’re a slow runner right now, you’re probably not engaging many of your fast twitch muscle fibers simply because the neural (brain to nerve) connections do not exist. However, the right training will train your brain to recruit more of the right fibers.

Okay, that’s Great. Now Tell Me What To Do.

As a runner, one of the simplest ways to engage more fast twitch fibers is to sprint train or intervals. This is why interval training is almost always included in running programs beyond beginners.

Fartlek training (which means speed play in Swedish) is a form of interval training that combines short speed bursts during a somewhat longer run. In addition to helping develop fast twitch muscle fibers, fartleks are great for improving overall aerobic endurance.

Another group of exercises are plyometrics which are explosive movements done repetitively. Examples are squat jumps, drop jumps, bounding or skipping. There are many different plyometric exercises available and you should choose those that resonate with you.

So pick some exercises, incorporate them into your training program 1 or 2 days per week with adequate rest time in between and watch your speed increase.

What Muscles Control How Fast You Run? by Jim Oldfield

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