Hypertrophy Explained Part One: The Nervous System

                I honestly think that the majority of the confusion that I alluded to in my blog post “The Mass Confusion” could be avoided if people knew and understood the actual mechanisms involved in the growth of skeletal muscle, and how they interrelate with one another. Unfortunately, very few personal trainers are even aware of these concepts, let alone the average gym member.

                Read a magazine, talk to your average personal trainer, or start up a conversation with another gym member, and many issues with regards to “getting bigger” will come up. Reps, weight, exercise selection, and other topics may be deliberated, but very rarely will you ever hear the actual physiological aspects involved with muscle growth discussed. I can honestly say that I cannot think of one time that the human nervous system has ever been a central aspect to any of the questions that I have received over the years. Before you can understand muscle growth, you must first realize that you are not training the muscular system when you are in the gym, you are training the neuromuscular system.

                Some quick anatomy/physiology background: The basic functional unit of the neuromuscular system is known as the motor unit. The motor unit is comprised of a somatic motor neuron (a component of the somatic nervous system) which branches out and connects to multiple muscle fibers at neuromuscular junctions. All of the muscle fibers in contact with this specific somatic motor neuron functionally act as a unit, hence the term motor unit. Each muscle fiber is comprised of numerous smaller fibers called myofibrils, and each myofibril is comprised of even smaller thin (actin) and thick (myosin) myofilaments. During a muscle contraction, these myofilaments slide along one another in small contractile units called sarcomeres that are arranged end to end in repetitive fashion along the length of the myofibril. This contractile action within the muscle fibers does not take place unless their postsynaptic receptors are activated by neurotransmitters, which are released into the neuromuscular junction site (the synaptic cleft) by the somatic motor neuron. The point here is that the nervous system is "the boss” so to speak, as it is in charge of deciding which motor units will be recruited to perform the contraction, how many will be recruited, as well as in what order. But how does all of this carry over to resistance training and muscle growth?

                The goal for most of us that begin resistance training is to increase the size and density of our skeletal muscle, which is the physiological process known as hypertrophy. Many get discouraged after a while because their strength is increasing week to week at a rapid rate, but when they look into the mirror there is no noticeable increase in the size/density of their skeletal muscle. This is a fundamental aspect of the process of skeletal muscle hypertrophy: An increase in the strength of your muscles will always precede an increase in the size of your muscles. This phenomenon is especially apparent when novice trainees are observed. This initial increase in strength is not from muscular hypertrophy itself, but from neuromuscular adaptations made by the nervous system. As a trainee progresses, his/her somatic nervous system becomes more efficient at recruiting multiple motor units for contraction, and synchronizing the order in which they fire, thereby increasing the muscles overall contractile ability. Further training also stimulates a neural adaptation in which the frequency of motor unit activation increases, thereby causing a more rapid “firing” rate of each individual motor unit. So regular resistance training will cause an increase the number of motor units recruited for contraction, as well as the rate at which they fire.

The most significant aspect of how the nervous system directly relates to the maximal stimulation of skeletal muscle hypertrophy is a concept that most of you should be familiar with. It is the neural adaptation of creating new and familiar motor engrams. The first time you attempt to perform a specific movement or exercise that requires significant neural activation throughout your skeletal muscular system, you will be uncoordinated, feel uncomfortable, and it will take a great amount of mental concentration. However, if you repeatedly perform that exercise or movement on a regular basis, it will become “second nature” to you, and you will be able to perform that exercise/movement with very little input required from your brain. A classic example of this is learning to ride a bicycle. At first, it is very difficult to learn how to balance and control the movement required to ride the bicycle successfully, and it also requires a high amount of mental concentration. After a few weeks or so, however, you can just get on the bike and ride down the street with almost zero conscious input from your brain. This is possible because your CNS creates a specific motor engram for that particular exercise/movement, and you no longer need to consciously force the muscular system to perform the activity. A motor engram allows your nerves to “remember” the specific motor unit recruitment and firing protocol required to perform the activity. The cool thing is that most motor engrams are permanent. If you go 20 years without riding a bicycle, it does not matter. Once you are on the bike your body will “remember how” to ride it with minimal brain input, and motor engrams are what make this possible.

These neural adaptations apply to all resistance training exercises, and translate into noticeable strength gains upon beginning a new workout routine. The muscle itself has not grown, or undergone hypertrophy, the nervous system has just become way more efficient at utilizing available motor units to perform the required muscular contractions. These initial neural adaptations are required before true hypertrophy can take place. Short term or transient hypertrophy is a temporary increase in skeletal muscle size during physical activity due to increased fluid levels within the interstitial and intracellular spaces of the myofibers involved with the contraction. Long term or chronic hypertrophy is a result of physical adaptations within the muscle cells themselves, which I will explain in part two.

The main point for part one here is that the human nervous system is what dictates the performance of your skeletal muscular system. Only by maximizing the efficiency of your nervous system can you in turn maximize the efficiency of skeletal muscular contraction, thereby maximizing your ability to stimulate hypertrophy. It is important to train correctly with proper form and cadence from the beginning of your resistance training experience. If you use incorrect form, a sloppy cadence, and place no consideration into ensuring that the target muscle/muscle group is bearing the greatest percentage of the stress, then you will be setting yourself up for failure. Doing so may result in the creation of motor engrams that are not efficient at utilizing the motor units within the target muscle itself, thereby causing you a very difficult time in stimulating hypertrophy in the tissue of interest.

End Part One