What are voluntary muscles?

Voluntary muscles, also known as “red muscles” or “striated muscles” are muscles of the human body whose contraction is regulated by voluntary brain activity (i.e. control by the will of the subject).

Voluntary muscles are divided into two categories: superficial and deep. Superficial muscles are mimic muscles, present only at the neck and head. Deep muscles, on the other head, are divided into skeletal muscle (moving bones under conscious control) and muscles attached to other organs (or to organs such as the eyes and ears/ tongue and pharynx). Each muscle fiber that makes up the voluntary muscle is connected to a nerve ending that receives orders from the brain; the latter through the release of a neurotransmitter, which in turn triggers a series of chemical reactions. It is then able to cause nerve stimuli that, transmitted by the motor nerve fibers, induce the contraction of the muscle.

Voluntary muscles can be classified according to their nodes of action. Agonist muscles are known as muscles that perform a movement by creating joint contraction, while antagonist muscles are muscles that oppose the action of another muscle. They include:

  • Flexor: muscles that contract and cause a joint to close
  • Extenders: muscles that contract and cause a joint to open


Abductor muscles are muscles whose contraction moves a limb away from the midline of the body, or from another part; while adductor muscles are muscles whose contraction moves a limb toward the midline of the body, or toward another part. Synergistic muscles involve two muscles that perform the same action. Voluntary muscles can also be classified according to their shape as well as the areas of the body where they are located (biceps, triceps, and quadriceps).

When at rest, muscles are neve fully relaxed. Under physiological conditions, they are characterized by moderate and constant voltage known as muscle tone or postural tone. A condition known as hypotonia (muscle tone below normal) is usually caused due to the reduction in the levels of potassium in the blood, whereas hypertonia (excessive muscle tone at rest) is a condition that is generally caused by the reduction of calcium levels in the body.

Diseases that affect the muscles and/or their nervous control include neuromuscular diseases. Problems can lead to spasticity or paralysis, depending on the location and severity of the individual’s condition. Also, a large number of neurological disorders can lead to problems relating to movement or motor coordination. Seeking the most appropriate form of treatment is essential in order to prevent further complications from arising.


What function do voluntary muscles serve?

The main function of the muscular system is movement. Muscles are the only tissue in the body that have the ability to contract and therefore move the other parts of the body. They also perform different functions such as: enable the body to maintain posture and body position (sitting or standing positions), stabilize and strengthen joints, as well as produce heat to maintain normal body temperature. Whether it is a facial expression or movement of the hand, tongue or finger, the main function of voluntary muscles is always the same: to allow the subject to perform muscle movements controlled by their own will.