How Muscles Work

Muscle is tissue that your body uses for movement and strength. The tissue is made up of a continuous chain (filaments) of muscle cells (also known as muscle fiber). The muscle cells consist of protein filaments (a chain of protein molecules) called myofibrils. The myofibrils consist of further filaments called actomyosin filaments. Actomyosin filaments are a combination of actin (thin filaments) and myosin (thick filaments). Your body contains roughly 650 muscles, depending on which expert you talk with.

A chain of events occur when your muscles contract (shorten). This chain of events is known as the sliding theory of muscle contraction. Muscle contraction begins when the actin and myosin slide over one another never changing their size. The myofibrils shorten when the actin and myosin slide over one another. The shortening of the myofibrils causes the muscles cells to shorten and creates muscle contraction.

Muscle contraction results from your brain sending signals, through the nervous system, to nerves running through your muscles. Your muscles are connected to the bones by tendons. When muscles contract they pull your bones. Muscles never push your bones.

Your muscles consist of agonist and antagonist muscles, which are located on opposite sides of your joints. Agonist muscles cause movements in limbs. Antagonist muscles cause limbs to return to their normal position.

This is why muscles only pull bones and never push. An example of this is with your hamstrings and quadriceps. Your hamstrings are agonist because the cause movement in your leg. Your quadriceps are antagonist, because they return the leg back to the normal position.

It's the major goal of body builders. It's a popular goal for people who strength train. But, how do muscles grow in size?

When you resistance train you cause micro trauma (tears) in the myofibrils. Your body goes into action when this micro trauma occurs. It repairs your myofibrils and adds new ones with body chemicals, proteins, and other nutrients. The resulting increase in myofibrils creates muscle growth.

When muscles contract they create tension. Enough tension causes damage to the muscle. The soreness you experience is likely caused from toxins in the damaged muscle. If the tension is too great, your muscles will rip and you will feel great pain.