The human body consists of 600 muscles that are attached to bone by tendons. The muscular system makes us capable of a variety of actions by contracting and becoming shorter. That is, in fact, all that muscles can do. They pull, but cannot push.

Skeletal muscle is the most abundant tissue in the body, making up about 23% of a woman's body weight and about 40% of a man's body weight.

Each muscle gets its instructions from the nervous system that is composed of the central nervous system (CNS) and the peripheral nervous system (PNS). The function of the latter is to continuously deliver information about all body parts to the CNS, the brain and the spinal cord, for processing.

The interaction between the muscular system and the nervous system makes out how we move and is subject to the study called "kinesiology";  the science of anatomy in action.

Because of the fact that a muscle can only pull means that it needs an  opposing muscle to bring it back in its resting length.

For example, when the biceps muscle in the upper arm contracts, it needs the triceps muscle to oppose that movement. This makes the biceps the prime mover or the "agonist" and and the triceps the "antagonist". A third category, the "synergists" are necessary to reduce or prevent undesirable movements that may occur while the agonist and the antagonist are doing their job.

It is important to realize that all muscles can play the role of agonist, antagonist or synergist. It just depends on the specific movement.  

In relation to fitness, it makes sence that the better one's muscular capacity, the more it contributes to one's level of fitness. Muscular capacity comprises strength, endurance and power. The better its condition, the more one is physically capable of and the more challenges one can withstand.

Muscles contribute to the level of fitness in more ways than with "just" movement, strength, endurance and power. Muscles are the real motor of human body in the sense that the better their condition, the better the condition of the human body as a whole.

If muscles get stronger the rest of the body cannot stay behind; it must follow accordingly. Think of it. If, with training, you would only improve your muscular system you would likely tear your body apart on the first forceful contraction of your muscles.

In other words a better devolped muscular system leads to:

• increased bone, tendon and ligament strength,
• improved joint function (flexibility),
• increased bone density (helps prevent osteoporosis),
• improved balance and stability,
• improved core strength (included reduced low-back pain) and posture,
• improved body control and awareness,
• improved function of the nervous system,
• Increased metabolic rate,
• increased cardiovascular and cardiorespiratory condition,
• reduced bodyfat levels.

And these are just some of the benefits. For as all bodily systems are connected, all will develop/improve proportially with the improvement of the muscular system. Realize however, that the opposite is true too.

Strength training is by far the best way to improve the cardiovascular condition. I will go more into detail on this on other pages of this website, but it is not hard to understand that the more muscles, the bigger the demand for oxygen and nutrients, the stronger a heart needs to be to meet with the demands of the muscles.

An increased metabolic rate is another consequence of an improved muscular system. One pound of muscles requires between 50 and 100 calories a day. Having said that, it makes sense that an increased metabolic leads to reduced bodyfat. All bodily systems interact with each other.

The muscular system plays a central role when you want to improve your level of fitness. An improved condition benefits all of the other components of fitness; the cardiorespiratory system, flexibility and body composition.

The next page is about flexibility, the third component of fitness.