Muscle and Motor Neurons

Movement matters. We are physical beings made to move — not sit behind a computer 8, 10, 12 plus hours a day.  The body falls apart when it doesn’t get the exercise it needs to stay strong, healthy, and lithe.  Bones weaken. Fat accumulates.  Joints stiffen and mobility diminishes.  Muscle, beautiful muscle, wastes away.  Use your body intelligently.  Move!

The human body is an adaptive system. That is, it remolds itself to meet the physical demands placed upon it. The SAID principle — Specific Adaptation to Imposed Demands. Said another way ;), a sedentary lifestyle produces a frail body more susceptible to injury and disease. A lifestyle that includes intermittent physically demanding workouts, nutritious food, and sufficient rest produces a body you will be proud to walk around in. There is hard science behind the effectiveness and benefits of resistance based exercise. Of the multitude of systems that make up your body, today I will talk two: muscle fibers and the nervous system. That is, the motor control system.

A benefit of resistance training I have yet to read about in fitness and health magazines is the importance of being in better control of your body. Improved body awareness and coordination could mean reacting quickly and catching yourself, and thus avoiding a painful fall because you didn’t realize the sidewalk ends abruptly. Or, it could mean saving your back, and weeks of painkillers, because you knew how to properly position your body when lifting and moving that couch.

By correctly training on the squat, deadlift, overhead press, and other compound multi-joint exercises — the so called “big lifts” — you are essentially training your nervous system and muscles to be more responsive. Since these exercises are functional in that they require you to use your body efficiently and in a manner it evolved to be used, this has a large carryover effect to life outside the gym. Put another way, because of the way you trained inside the gym, you’ve built a stronger and more coordinated body that better meets life’s demands outside it.

All a muscle can do is contract when stimulated from the firing of motor neurons. That’s it. Though there is considerable more taking place to enable human movement, here are two similar (in that they’re discrete) but different analogies to describe the same function; how the nervous system and muscle work to produce movement:

  1. A light switch.  The light is either turned on or turned off; there is no in-between state.  The same holds true for muscle and the associated muscle fibers that make it up.  The action potential from when a motor neuron fires is either great enough to cause the muscle to contract, or it is not.

  3. A flight of stairs.  At the bottom of the stair case reside your Type I slow twitch muscle fibers that  don’t require a strong neural drive to contract.  They are relatively small in diameter and do not produce much force, but they can work for a long time.  These are the fibers that come into play when performing weightlifting sets of 15 plus repetitions, or when slaving away on the elliptical machine for hours on end in the pursuit to burn fat. Climbing the stairs, near the top reside your Type II fast twitch fibers; to contract these require a strong neural drive in terms of both magnitude and frequency of motor neuron firing. Type II fibers are associated with fast, explosive movements such as performing the snatch exercise, or saving yourself from a debilitating fall because of that damn sidewalk. Though strong and powerful, these fibers are subject to quick fatigue.

The human body on average is made up of 50% of each muscle fiber type. As you may surmise, by not exercising at all or maybe by focusing only on low intensity endurance type exercises, you are leaving out a big part of the fitness equation. Namely, the heavy explosive lifts and the strong neural drive required to activate Type II muscle fibers and the benefits associated with stimulating them. So, why does movement matter? Your quality of life depends on movement, and at times so does your safety. By using a sound science backed approach to physical conditioning and including the “big lifts”, you can build a body that looks great and responds just as well.

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