How Skeletal Muscles Work

how do skeletal muscles function

By John Cardillo, Body Building Champion

In order to make our skeletal muscles work, we send messages from the brain via nerve impulses through our central nervous system to particular muscle fibres commanding them to contract (shorten by contracting). The nerve endings fire bursts of energy into the fibres. As a result, they contract and pull on our tendons, which then move the bones, thereby allowing us to move around. During exercise, muscle fibres contract to their fullest extent, not just partially – a fact that is the basis for what’s called the all-or-none law of muscle physiology. This does not mean that all the muscle cells/fibres contract when movement occurs, but the fibres that do contract do so to their fullest capacity.

The demand placed on the muscle determines how many muscle fibres are called into action to contract simultaneously and complete the task. Logically, the more difficult the task or exercise, the more muscle fibres are activated. Intense muscle contractions cause small tears in the Actin and Myocin. They will have to repair themselves once the activity ends. If you do light exercise, you need little effort, so fewer muscle fibres will be activated. This cycle continues, as muscles contract and repair themselves over various periods of time in anticipation of future intense work that may be asked of them.

Our bodies expend the least amount of effort possible to complete a task. When we exercise, in addition to the muscle fibres needed for the task, other muscle fibres may become involved indirectly, but are not stimulated in a major way. The muscles in our body are arranged in groups that usually work in pairs to perform opposite movements. An example is the bicep, or the upper arm, which we use to lift something up (to bend the elbow). This muscle has behind it the triceps, which we engage when we push something down (to straighten the elbow).

Whenever we go to the gym to exercise, whether it be weight training, swimming, running or bicycling, we perform repeated, co-ordinated movements that originate in our brains. As we gain experience doing the exercises we love, we get better and better at it because our brains learn to send the messages more efficiently, and this improves our skills. Just like learning to ride a bicycle, exercise movements at first may feel a bit awkward or uncoordinated, but after a few sessions, movement will feel much smoother and productive.

During high-Intensity HIT3 exercise, our muscle fibres contract to perform each repetition, and they use primarily energy supplied the cells ATP cycle, produced from stored glycogen. As we continue to exercise, however, glycogen becomes depleted. Exercise, as performed as per my HIT3 fashion, increases the uptake of glucose from the bloodstream or from the liver storage. The harder the repetitions (contractions) performed during the latter part of a set of exercise, the more glucose will be used by the muscles being worked.

How Muscles Grow

The larger a muscle is, the more force it can generate on the bone to which it is connected. The role of nerve impulses in human movement is critical; therefore, healthy muscles depend on a healthy nervous system. This is achieved by resting between workouts to allow the muscles and their associated nerve endings to recover from the demands of HIT3 exercise.

When we place demands on our muscle cells and they contract, they in fact cause minute tears in the muscle fibres. Muscles are self-healing, and it is the healing process during the rest between exercise sessions that allows muscles to actually grow. The muscle cells’ growth fills in the tears, adding strength and size to the muscle that is repairing itself.

To engage as many muscle cells as possible during an exercise movement, we need to use the most resistance we can handle without hurting ourselves. By using high intensity of effort and performing an exercise in strict form with progressively heavier weight, we call to action a maximum number of muscle fibres, eventually requiring more recuperation and to facilitate cell repair and growth. Performing light exercises that involve high numbers of repetitions with minimal resistance will benefit you in only a small way. It simply doesn’t call on enough muscle cells to contract fully and stimulate muscle cell growth.

Our nervous system is fundamental to our skeletal muscles, and the amount we exercise affects the nervous system. Performing progressive resistance hi-intensity exercises that contract as many muscle fibres as possible to muscular fatigue (until you cannot perform another repetition) means you have reached the limit of strength and muscle fibre contractions at that moment. Training in this fashion is the most important principle of the HIT-3 workout system,

Long, laboursome workouts involving performing too much exercise per body part are counterproductive and lead to overtraining (over-stimulus), which will in fact, cause the muscle fibres to get smaller and weaker.

How Muscles Atrophy

Sometimes the nerve supply to a muscle is damaged because of an accident. This will lead to the muscle fibres becoming smaller and therefore weaker. Exercising too much, which is referred to as overtraining, can also exhaust a muscle to such a degree that it loses the ability to contract effectively. This will cause a muscle cell to become smaller and weaker. In both cases, the muscle will reduce in size. In sedentary people who perform no exercise or muscular demanding tasks, the muscle becomes inactive and reduced in size, also an example of atrophy. Inactivity (the non-use of muscles), will lead to muscle weakness and wasting. This effect occurs since our bodies adapt with lesser or more strength, according to the demands of exercise or work that we ask them to perform, or to the lack of exercise or work. That is why the right type of hi-intensity exercise is key to maintaining muscular size and strength, especially as we age.

John Robert Cardillo is a well known and respected Bodybuilding Champion from Canada, who also specializes as a Workout expert. Cardillo is thought of as a real trailblazer when it comes to Hi-Intensity training. He was involved in the development of the HIT3 workout, as well as the SHREDDED NUTRITION program.

He is also responsible for the TRANSFORMATION MASTERY program, which is unique system that combines the HIT3 workout system with the SHREDDED NUTRITION diet.

For more information, please visit



James Williams
James is our Lead Content Publisher here at Feeds Portal. He has worked with many top websites over the years, including BuzzFeed.

Log In

Forgot password?

Forgot password?

Enter your account data and we will send you a link to reset your password.

Your password reset link appears to be invalid or expired.

Log in

Privacy Policy

Add to Collection

No Collections

Here you'll find all collections you've created before.