The Musculoskeletal System

How it Functions


Physical therapists work with the musculoskeletal system, evaluating, diagnosing and treating disorders.

The musculoskeletal system is a complex, interactive system that includes bones and soft tissues, including joints, ligaments, tendons, muscles and nerves. This system is composed of soft and hard connective tissues, which serve two basic functions: structural integrity and stable mobility.

The musculoskeletal system's primary roles include supporting the body, allowing motion, and protecting vital organs, such as the brain, heart and lungs. It includes the skeletal and soft tissue systems.

The skeletal system, which includes bones and joints, makes up the body’s supporting structure:

  • Bones are rigid organs that support and protect body organs, produce red and white blood cells and store minerals. Bones come in a variety of shapes, are lightweight yet strong and hard, and serve multiple functions. They are composed of calcium, phosphorus and sodium, along with the protein collagen. There are 206 bones in the adult human body.
  • Joints make movement possible. They are found at the location at which two or more bones make contact, and are designed to allow movement and provide mechanical support.


Just as important is the soft tissue system, which stabilizes bones and joints allowing them to move. A restriction anywhere in the soft tissue system can affect a patient’s mobility and ability to function. The system includes four types of tissue.

  • Muscles contract to move bones and joints.
  • Ligaments are fibrous tissues that connect bone to bone.
  • Tendons connect muscles to bones.
  • Fascia is a fibrous, web-like tissue throughout the body, often keeping organs in place.


Most muscles work in pairs. During a movement, the muscle responsible for moving a body part contracts or shortens. It acts against or in opposition to another muscle, which then is responsible for moving the body part back to its original position.

Major body areas that function in this manner include the chest and back, the front and back of the shoulder, the upper back and shoulder, the abdomen and lower back, the left and right side of the abdomen, the front and back of the thigh, the shin and calf, the top and underside of the upper arm, and the forearm.

Ligaments gradually lengthen under tension, and return to their original shape when the tension is removed. However, they cannot retain their original shape when stretched past a certain point or for a prolonged period of time. Athletes perform stretching exercises to lengthen their ligaments, making their joints suppler.

Tendons work in concert with muscles, but are subject to many types of injuries due to overuse. These types of injuries generally result in inflammation and degeneration or weakening of the tendons.

Fascia surrounds muscles, groups of muscles, blood vessels, organs and nerves. Muscle fascia reduces friction, making muscles more efficient by allowing them to easily glide over each other.

All this movement is coordinated and controlled by the nervous system. Nerve cells or neurons help regulate the signals between the muscles and tendons, and the brain and spinal cord. Muscles contain receptors that receive messages from the nervous system, and moderate the muscle movement.

When a limb is relaxed and manipulated, a physical therapist can often detect underlying problems in the musculoskeletal system. Then a therapist can begin treating, healing and strengthening the parts of the body that aren’t working properly.