Strength training and intramuscular coordination
Strength training doesn’t make a beginner stronger just because the muscle immediately grows bigger. The first visible progress often comes from the nervous system: the body learns to make better use of the muscle it already has.
When people say that neural adaptation drives the strength gains in the first 6–10 weeks, it sounds complicated. The actual idea is simple: the brain, nerves and muscles start working together more precisely on the same movement.
Why do you progress so quickly at the beginning of strength training?
A beginner walks into the gym, and within a few weeks the weights are going up. That doesn’t yet mean the muscle has grown much bigger. A large part of the progress comes from the body making better use of the muscle fibers it already has.
This phenomenon is called neural adaptation. It happens through both intramuscular and intermuscular coordination mechanisms. Here we focus on the intramuscular side: what happens inside a single muscle as the effort becomes stronger and the movement becomes more secure with practice.
It’s also important to know that intramuscular coordination doesn’t improve only at the start of training. It keeps developing later on as your training age grows. The difference lies in whether the progress comes more from better functioning of the nervous system or from metabolic changes. This is influenced by factors such as rep count, set length and the weight used.
Strength training and the motor unit
Before we can break down intramuscular coordination, you need to understand one basic concept: the motor unit. It means an alpha motor neuron and the muscle fibers controlled by that same nerve cell.
The nervous system controls muscle work. Higher-level control starts in the cerebral cortex, but the command reaches the muscle via the spinal cord. The long axons of the upper motor neurons in the cortex don’t go straight into the muscle; instead, they act on the lower motor neurons in the spinal cord, also known as alpha motor neurons. Only the axons of these neurons travel within the nerves to the muscles, where they branch out and connect with muscle cells.
A neuron can be very long. In humans, the length of a neuron can exceed 1 m. A neuron usually has 1 long axon, which carries signals away from the cell body, and several dendrites, which receive signals. It is the communication network of the nervous system, not just a single wire.
The muscle fibers belonging to the same motor unit are all of one type and contract at the same time. The motor neurons of slow motor units are smaller and innervate 10 to 180 muscle fibers. The neurons controlling fast muscle fibers are larger, and each of them controls the work of 300–800 muscle cells on average.
The number of muscle fibers also depends on the muscle’s function. In the eye muscles, where movement has to be extremely precise, there are about 15 muscle fibers per motor unit. In large muscles, such as the gastrocnemius, a single motor unit can contain as many as 20003000 fibers. So from the nervous system’s point of view, not all muscles are alike.
How does strength training teach a muscle to work?
Intramuscular coordination improves mainly through three mechanisms.
- An increase in the number of active motor units.
- Regulation of the motor units’ firing rate.
- Synchronized recruitment of motor units, meaning how they are brought into action.
In practice, this means a muscle doesn’t always work at full capacity. Different types of motor units kick in depending on how much strength is needed. At low loads, slow oxidative fibers, also known as type I fibers, are mostly enough. As the load increases, faster oxidative-glycolytic fibers, or type IIa, are added. At the greatest effort, glycolytic fibers, or type IIb, come into play as well.
That is why motor units made up of type I fibers are the ones the body uses most often. Type IIb muscle fibers are recruited less often, because they are needed only when the effort is maximal or very close to it.
To be honest, there is one important nuance here: even at very high effort, a person doesn’t usually activate all motor units at once. Even a heavy set at 85% or more of your maximum doesn’t mean the full potential is in use.
Here’s an analogy. Imagine 10 people pulling on a rope, but 4 of them are only holding on and not really pulling. After practice, 7 people may be pulling actively, later 8. If 8 people pull instead of 6, the result is immediately stronger. Something similar happens in a muscle.
If a biceps had, say, 100 muscle fibers, but only 80 took part during maximal effort, some of the strength would go unused. Over time, training pushes more of those fibers to contribute. That still doesn’t mean 100% of the potential is constantly available in an ordinary situation. The body always keeps a certain reserve.
In practice: what to pay attention to in strength training
If your goal is to build strength, your training has to give the nervous system a clear signal. Work that is too light doesn’t require activating a large number of motor units. Heavier, technically clean work teaches the body to use more muscle fibers at once.
That doesn’t mean every workout has to be maximal. Beginners benefit most from consistency, good technique and raising the weight gradually. If the movement breaks down, the body no longer learns to produce strength better, but to compensate.
The simple truth: getting stronger isn’t only about muscle size. Just as important is how well the nervous system drives that muscle. That is why a person can progress quickly at the start even when the mirror hasn’t changed much yet.
Link to the original source: Reference.
FAQ: strength training and neural adaptation
Does strength increase at first without any gain in muscle mass?
Yes, partly. During the first weeks, much of the improvement comes from the nervous system: the body activates muscle fibers more efficiently and the movement becomes more stable.
Why don’t all muscle fibers work at the same time?
The body uses muscle fibers according to need. Under a light training load, it makes no sense to call on maximal reserves. A very large effort recruits more motor units, but usually not all of them.
Does this progress continue in advanced lifters too?
It does, but more slowly. As training experience grows, progress comes more from the interplay of several factors: the nervous system, muscle mass, technique and how the training is structured.
Author: Janar Rückenberg
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