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Anatomy & Physiology - Body Systems

The Muscular System

The branches of science that will help you understand the body parts and functions are anatomy and physiology. Anatomy deals with studying the human body (the components, structure and position), and physiology is the study of how the body functions.

Body Systems

The body comprises several systems: The Cardiovascular system, Digestive system, Endocrine system, Muscular system, Neurological system, Respiratory system and Skeletal system.

The Muscular System

Muscle tissue has four main properties: Excitability (ability to respond to stimuli), Contractibility (ability to contract), Extensibility (the ability of a muscle to be stretched without tearing) and Elasticity (ability to return to its normal shape).

Through contraction, the muscular system performs three essential functions:

  • Motion - walking, running etc.
  • Heat production - maintain normal body temperature
  • Maintenance of posture - standing, sitting etc.


To understand how the muscles combine with the skeleton to provide motion, we must look at the movement's basic mechanics. The main framework of the body is covered by muscle, whose function is to permit movement. We know that to move or lift a load against another force, it is easier to use levers, and it is this principle that the musculoskeletal system adapts and that we must examine.

The parts that are used in a lever are as follows:

  • Lever - nearly always the bone
  • Fulcrum - the pivot point of the lever, which is usually the joint
  • Muscle Force - a force that draws the opposite ends of the muscles together
  • Resistive Force - a force generated by a factor external to the body (e.g. gravity, friction etc.) that acts against muscle force
  • Torque - the degree to which a force tends to rotate an object about a specified fulcrum

There are different types of levers dependent upon the position of a fulcrum, effort and resistive force.

First Class lever: Muscle force and the resistive force is on different sides of the fulcrum, e.g. the head resting on the vertebral column. As the head is raised, the facial portion of the skull is the resistance, the fulcrum is between the atlas and occipital bone, and the effort is the contraction of the back's muscles.

Second Class lever: Muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through the level longer than through which the resistive force acts - e.g. raising the body up onto the toes. The body is the resistance, the ball of the foot is the fulcrum, and the effort is the calf muscle contraction.

Third Class lever: Muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through the lever shorter than that through which the resistive force acts - e.g. adduction of the thigh. The thigh's weight is the resistance, the hip joint is the fulcrum, and the adductor muscle contraction is the effort.of the adductor muscle is the effort.

Most of the limbs of the human body are articulated by third-class levers.

Agonist, Antagonist, Fixator & Synergist Muscles

Muscles can only exert a pulling force, so work in pairs. When we move a limb one muscle, the agonist muscle, also known as the prime mover causes the movement and an antagonist muscle works in opposition to the agonist muscle.

Example: Biceps curl - the biceps is the agonist muscle causing the movement, and the triceps are the antagonist muscle working in opposition to the biceps.

A fixator muscle's function is to stabilize the agonist muscle's origin so it can move efficiently.

Other muscles, known as synergist muscles, stabilize muscle movements to keep them even and control the action so that it falls within a range of motion which is safe and desired.

Heat production

Muscle contractions produce heat, and as much as 70% of body heat is produced by energy produced in muscle tissue. Blood is an essential element in temperature control during exercise, taking heat from the body's core and working muscles and redirecting it to the skin when the body is overheating. When the body's internal heat reaches too low, a level of thermoreceptors in the skin relays a message to the hypothalamus in the brain. In response to this signal, the skeletal muscles contract and relax involuntarily (shivering), increasing muscle activity to generate heat. In turn, muscles are also responsive to exterior heat - cold air improves muscle tone, and hot conditions have a relaxing effect on muscles.

Maintenance of posture

As well as enabling movement, muscles also maintain posture and body position. Sensory receptors in the muscles monitor the muscles' tension and length and provide the nervous system with crucial information about the location of the body parts, therefore enabling posture to be maintained. Muscles are never entirely at rest, nor do they have to shorten in length when they contract. The tension or tone produced due to these contractions between opposing muscle groups helps us remain in a static position, even when we are asleep.

Muscle Origin & Insertion

Each muscle end is attached to a bone, and these connections are known as the origin and insertion. The muscle's origin is attached to the immovable bone, and the muscle's insertion is attached to the movable bone.

Effect of exercise on the muscular system

The effects of regular exercise on the muscular system:

  • Strengthens muscles and the connective tissues
  • Improves muscle control and balance
  • An increase in muscle size and efficiency
  • The amount of myoglobin within skeletal muscle increases
  • Muscles are capable of storing a larger amount of glycogen
  • Muscle became more efficient at disposing of waste products through the bloodstream
  • Increase in muscle recruitment

Page Reference

If you quote information from this page in your work, then the reference for this page is:

  • MACKENZIE, B. (2001) Physiology - Muscular System [WWW] Available from: [Accessed