Functions of Muscles

Working together, the muscles of the body perform several essential functions.

1. Movement

Muscles give the body strength, and by contracting and relaxing they produce every kind of movement. Movement can be broadly divided into gross movement, such as walking, and fine movement, such as writing. Most movements are produced not by one muscle alone but by groups working together: an agonist (prime mover) does the main work, an antagonist on the opposite side of the joint relaxes to let the movement happen (and can reverse it), and synergists assist or stabilise the joint - for example, the quadriceps and hamstrings act as agonist and antagonist in turn as a runner's knee extends and flexes with every stride.

2. Maintenance of posture

Muscles help us hold our body posture, whether sitting or standing. Good, strong muscles let us maintain a good posture; weak muscles lack the strength to hold one. Many postural muscles, such as those of the back and core, work almost continuously at a low level throughout the day without us noticing, which is why they fatigue and ache when posture is poor for long periods.

3. Heat generation

Muscles help maintain body temperature. Whenever body heat falls, the skeletal muscles begin to contract to bring it back to normal - for example, shivering is rapid muscle contraction that warms the body. The reverse is also true during exercise: hard-working muscles generate a great deal of heat as a by-product of contraction, which is why the body sweats to cool itself and why athletes need to replace fluids lost during prolonged exertion.

4. Respiration

A muscle called the diaphragm drives breathing. When it contracts, the chest cavity gets bigger and fills with air; when it relaxes, the chest cavity pushes the air out. This is how the exchange of gases is made possible. During vigorous exercise, additional muscles between the ribs (the intercostal muscles) also assist breathing to move more air in and out, matching the body's increased demand for oxygen.

5. Constriction of organs and blood vessels

The contraction of smooth muscle moves nutrients through the digestive tract, passes urine out of the body, and propels secretions out of the glands.

6. Pumping of blood

The heart pumps blood, and the smooth muscle in the walls of the veins and arteries helps move blood between the cells and the heart.

Why muscle function matters in training and injury prevention …