Disclaimer: nerd alert, requires a lot of attention, my native language is Russian - so please accept my apologies in advance had I misused the English language or allowed some typos.
Our body is a very complex mechanism that features vast functionality and a variety of individual skills. Whereas the muscles, bones, and connective tissue play a crucial role in it, nothing will be possible without the brain and the nervous tissue.
Everything we do starts inside the brain in the form of chemical-electrical activity, which is transmitted to the body parts we are about to engage. It is worth noticing that the brain is in charge of many other processes such as digestion, respiration, metabolism, sleep, etc., but we will talk only about its involvement in muscle-related activities.
To communicate with the body, the brain uses a highly ramified network of the tissue we know as nerves. For example, if we want to walk, run, or jump - first, the brain needs to generate electrical signals and send them to the corresponding muscles. Only after that, we can expect any activity to happen. The brain also receives signals from the body parts to monitor their current state and control movement outcomes. This incoming information is called biofeedback. There are two primary means by which the brain sends the signals to run various processes within the body:
The chemical-electrical impulses, propagated via the nerves and produced by the neurons, the interconnected cells inside the brain, and the spinal cord.
The hormones, chemical compounds, transported via the bloodstream, and manufactured by the major glands, parts of the endocrine system. These chemical messengers are delivered into the targeted cells and affect their intrinsic activity in the way the brain deems necessary.
We have two main nervous systems: central and peripheral. The central nervous system (CNS) consists of the brain and the spinal cord. The latter has myriads of nerve breaches spread into the body, including the muscles, joints, and inner organs. These branches comprise the peripheral nervous system (PNS). A couple of more nervous systems exist, but they are subdivisions of the PNS. For the sake of simplicity, we will omit them.
The significance of brain involvement in everyday fitness is much overlooked. In pursuit of better well-being, we often focus on muscle training: muscle strength, muscle power, muscle flexibility, muscle coordination, and so on. You might be surprised to learn how little the muscles themselves are responsible for all of it. Let’s have a detailed look at the fitness aspects we talked about in my previous post. But first, let me address the burning question of how we gain the muscles.
To gain muscle mass, we need to lift weights. Sometimes it works, sometimes it does not. Especially after the age of 25, we see a significant decrease in our ability to put on badly wanted lean mass. What is the matter? The conventional theory is the following.
When we lift weights, we slightly overexert the muscle tissue, creating micro-tears inside. In other words, we cause damage to the muscle cells’ inner structure. Luckily, it is repairable. The damaged cells produce biochemical compounds leaking from them. These compounds interact with the other chemicals in the vicinity sending the biofeedback to the brain about the damage which triggers this chain of reactions:
The hypothalamus, a part of the brain, responds by producing hormones, which go to the pituitary gland, also located in the brain.
The pituitary gland produces other hormones that go to the testes. The latter secrete around 95% of testosterone.
When the testes receive the pituitary hormones, they increase testosterone production.
The extra testosterone goes into the damaged muscle cells via the bloodstream.
Every cell in the body, including the muscle cells, has a nucleus. The latter stores our DNA. The DNA is a very long molecule, shaped like a double-helix and comprised of millions of chemical elements, called nucleotides. These nucleotides form sequences of different lengths, known as genes. The DNA has 20 000 - 25 000 genes; most of them have protein-coding functionality. The genes tell the body how to build different proteins from amino-acids derived from food (the proteins we consume are disassembled into amino-acids and reassembled in a different sequence according to the genome code to form the body’s native proteins).
Upon arrival into the damaged muscle cell, testosterone goes into its nucleus.
Inside the nucleus, a molecule of testosterone binds with a specific gene that provides coding instructions on how to assemble a protein for this particular cell thereby initiating protein-production using amino-acids taken from the bloodstream.
After the assembly has finished, the new protein molecule is ready to be structurally incorporated into the cell to repair its damage.
Muscle growth occurs.
It is a long process with quite a few steps. Here is a condensed version of it:
lifting weight -> muscle cells damage -> extra testosterone production -> the gene activation -> new proteins assembly from available amino-acids -> damage repaired with the new proteins -> muscle growth happens
We can see that the key component of muscle growth is testosterone. Unfortunately, with age, the testes' ability to produce testosterone declines significantly. With not enough testosterone, there will be no gene activation, consequently no new protein assembly, therefore, no muscle growth. Even if the bloodstream swarms with amino-acids, the laying bricks of proteins, there will be no “workers” to lay them.
At a young age, the level of testosterone is much higher to facilitate tissue growth while the organism is still taking its final form. That is why in your teens, almost any sports activity produces a noticeable result for the body's musculature. In early adulthood testosterone level starts declining, making it harder to assemble new muscle cells and repair their internal damage caused by physical activity. There are other factors limiting muscle growth, but testosterone reduction is the most significant of all. In a way, it is a natural body's mechanism to prevent the tissue from constant development.
In no way, I want to discourage you from lifting weights. There is a potential for some muscle growth at any age, especially if one has no previous experience of weightlifting. Genetics is enigmatic and might still facilitate some gain. However, this gain will be a far cry from a professional bodybuilder's musculature. It is crucial to set our expectations right.
After the muscle formation has finalized, it is crucial to continue training to maintain and improve what we gained starting with strength.
In my last article, we have already defined what strength is - the ability to produce the force required to overcome an object’s weight. That force is produced by the muscles, more precisely by contraction of their inner structures.
The inner structures are protein filaments, called myofilaments.
The myofilaments are bundled into myofibrils.
The myofibrils are grouped to form a muscle cell or muscle fibre.
The muscle cells are arranged into a muscle fascicle.
The muscle fascicles are packed into a single muscle.
You can think of a muscle as tiny wires (myofilaments) within slightly bigger telephone wires (myofibril) inside big telephone wires (muscle cells) bundled up to make huge telephone wires (muscle fascicles) which wrapped around by electrical tape into a vast single cable - the muscle itself. (Pic. 1)
The myofibrils are divided into compartments, called sarcomeres, where each of them has myofilaments, protein structures: actin, myosin, and titin. The actin and myosin are partially overlapping with each other. (Pic. 2)
When the electrical impulses, generated by the CNS, reach the muscle, the actins and myosins in each sarcomere start pulling against each other using their cross-bridges, thereby producing muscle contraction. When the electrical activity ceases, the actin and myosin filaments stop interacting and the muscle completely relaxes. Without the participation of the CNS, no muscle activity is possible, no pulls are produced.
Stepping aside from the topic, I need to mention that during lifting weights we cause damage to the myofilaments (actin and myosin), which the body repairs resulting in their extra thickness or quantity - the muscle gain.
The fact that the muscles need commands from the CNS to produce any activity makes them the receiving side. Now let's have a look at the related organization of the sender, the CNS.
As we already know, the CNS is constituted from the brain and the spinal column; both are composed of nervous cells (neurons) and their interconnections. A neuron sends and receives information (electrical activity) to and from other neurons. It does so using an axon (only one) and myriad dendrites. The dendrites are used for inbound information, and the axon is for outbound information. Whereas a neuron might have hundreds of thousands of dendrites, it has only one axon (pic. 3).
Among these neurons, there is one type of great interest for us - the motor neurons. They are located in the motor cortex (a part of the brain), brainstem (another part of the brain), and the spinal cord. A motor neuron can have hundreds or even thousands of connections with the muscle cells. The number of muscle connections varies from neuron to neuron. Some might have only a few, and others might have quite a few.
As mentioned before, a neuron has only one axon. A motor-neuron axon connects to a muscle and can ramify on the other end connecting its neuron with many other muscle cells at once. Bifurcation of a single axon is interesting because it means that once the neuron starts generating outcoming electrical signals via its only axon, those signals will be delivered to all muscle cells associated with this motor neuron, thus simultaneously activating all muscle cells linked to this particular motor-neuron. The compound of a motor neuron and its muscle cells is called a motor unit. (Pic. 4)
Now, after we got some idea of how the muscles are structured and connected to the CNS, we can have a look into the strength concept.
When the motor neurons are firing, sending electrical currents down along their axons to their muscle cells; the latter are responding with contraction producing a muscle pull. The strength of the pull does not depend on the power of the electrical stimulus. If the stimulus is above a certain threshold ( -70 mV known as resting potential), the muscle cells fire generating maximum pull. This principle is the all-or-none law. However, there are factors the strength of the pull will depend upon:
On the side of the CNS:
The number of motor neurons in the CNS. The higher the number, the more neurons can be potentially involved to generate a single contraction. Nevertheless, this factor is genetically predetermined and varies only slightly amongst individuals.
The number of motor neurons active at the time of muscle exertion. The more neurons are active, the more muscle cells can be recruited.
Quantity of connections with the muscle cells each acting motor neuron has. The all-or-none law states that once the motor neuron fires, it excites all associated muscle cells to their max. Therefore, the more muscle cells connected to a single-acting motor neuron, the stronger contraction is produced.
The firing frequency of the motor neurons. If the firing frequency is high, then the muscle cells produce individual twitches with less delay in between. As a result, those twitches supe