When it comes to building strength, the first place in the body people often think of is the muscles. After all, these are the main tissues involved in coping with loads of all kinds, and it’s relatively easy to feel and see how the presence of muscle corresponds with greater capacity to load. But it turns out the power the muscles afford the body originates elsewhere—in the brain, technically the central nervous system (CNS)—which is a reason to reconsider one’s approach to strength training, as well as its possible benefits.
What Muscles are Made Of
Before we get into the mechanics of how muscles work, let’s start with their basic structure and anatomy. Muscle fibers (which is what we call “muscle cells”) appear throughout the body in bundles. You can think of individual muscle fibers like pipe cleaners, as I demonstrate in this video, which is part of a longer course I created for a course in my Virtual Studio called Strength Science 101.
Each fiber in a bundle is innervated by a motor neuron—the passageway that transmits signals from the CNS to the fiber. All of the fibers and motor neurons of a bundle together comprise a motor unit, which will always fire together.
Motor units (and muscle fiber bundles) come in all sizes, as I show in the video. Some have fewer fibers and some have more, but muscle fibers of high threshold motor units make up the majority of a muscle’s mass. Meaning: most of our muscles are made of big bundles. Meaning: if we want to access most of our muscles, we need more powerful movement.
How Muscles Work
Getting muscle bundles of any size to “work” (by which we generally mean contract, or produce force) requires the same process. First, the CNS will send a signal along the motor neuron to the muscle fiber—a process called central motor command or neural drive. If the signal fires, all all those muscle fibers connected to the motor neurons will contract.
Muscle contraction happens at the place where the muscle fiber and motor neurons meet—called the neuromuscular junction. Muscle activation is a little different—it happens at the level of the whole motor unit. Both, however, require a clear connection to the CNS.
So, if we want to get stronger, and strength requires CNS signals, can we simply think our way to strength? Not quite. What we do see, though, is a direction connection between exposures to activities/movements that require strength and capacity for muscle activation, and by extension muscle contraction.
The Brain-Brawn Connection
People who strength train in some capacity are simply able to access a lot more of their muscle fibers.
People who don’t strength train leave a lot of muscle fibers sitting there doing nothing. This becomes a bigger problem after age 30. The old use it or lose it phenomenon speeds up and those unused muscle fibers go, “I guess I’m not needed here.”
Then they go away!
But when we start a new movement practice—especially one that requires strength—we get to access muscle fibers that previously went untrained. Because those fibers were already there, like rooms behind closed doors in a house, you can discover a whole new way to experience your body, but without having to move to a new house or even renovate the old one.
Accessing these hidden rooms requires that our brain send bigger signals. The CNS (central nervous system) is queen!
This starts with giving the queen a reason to send bigger signals—like exposing our body to higher effort activity, like lifting substantially heavy weights. And like anything you do repeatedly, with practice, the bigger the signals our brain sends, the better it gets at sending big signals.
Our neural drive improves. So does our strength. And together, we feel more capable of exploring areas of life even beyond our home. There are fewer consequences for hard work, spontaneous adventure, or that pick up game of basketball with your nephews.
The thing to remember is that, in this case, the size of our signals (determined by loads) matters. Because of how muscle activation works—motor units are recruited from small to large—if I never engage in effortful enough activity, I never get to activate the majority of muscle fibers (of the large “high threshold” motor units). If I never cross the threshold to effortful—let’s say I only do life activities plus things like yoga and Pilates—the high threshold motor units don’t get used, and the majority of my body’s total muscle mass goes largely untrained.
That’s a lot of closed doors and undiscovered space.
Again, this use it or lose it phenomenon explains sarcopenia—the involuntary loss of muscle mass and strength—as we age. While sarcopeonia is a natural outcome of aging, by strength training, we slow down the process exponentially.
In other words, we extend the quality of our life by ensuring our own physical capacity, which is our ability to participate and engage to the fullest in the activities of our life that are meaningful to us. With more load, more muscle activation, and more muscle contraction, we have more options for how to live our lives.
What used to be heavy is light.
What used to seem impossible is possible.
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