The musculo-skeletal system and its role in movement

The skeletal system provides the framework for the body, but it cannot create movement by itself. It works closely with the muscular system to allow actions like walking, running, or lifting. Together, these two systems form what is known as the musculo-skeletal system.

During physical activity, muscles need a steady supply of oxygen to function and produce movement. The heart plays a key role here by pumping blood that carries oxygen to the working muscles.

How muscles attach to bones and enable movement

Muscles are connected to bones through strong, fibrous tissues called tendons. These attachments allow muscles to pull on bones, creating movement at joints. When a muscle contracts - meaning it shortens and generates tension - it tugs on the tendon. This pull then moves the bone, resulting in actions like bending an arm or extending a leg.

Muscles can only pull; they cannot push. This limitation means that movement in opposite directions requires coordinated effort from different muscles. Each muscle in the pair attaches to two bones via tendons, but during movement, only one bone at the joint typically shifts, while the other remains stationary.

Major muscle groups and their functions

The body has several key muscle groups that perform specific movements at various joints.

Key muscle groups and movements

• Pectorals - Located in the chest; responsible for adduction and flexion at the shoulder.
• Deltoids - Found in the shoulders; enable flexion, extension, abduction, or circumduction at the shoulder.
• Trapezius - In the upper back and neck; performs extension at the neck.
• Abdominals - In the core; allow flexion at the waist.
• Biceps - On the front of the upper arm; cause flexion at the elbow.
• Triceps - On the back of the upper arm; produce extension at the elbow.
• Quadriceps - On the front of the thigh; enable extension at the knee.
• Latissimus dorsi - In the mid-back; facilitate extension, adduction, or rotation at the shoulder.
• Gluteals - In the buttocks; handle extension, rotation, and abduction of the leg at the hip.
• Gastrocnemius - In the calf; allow pointing the foot downwards (plantar flexion).
• Hamstrings - On the back of the thigh; perform flexion at the knee.

Antagonistic muscle pairs and their coordination

To achieve movement in two directions at a joint, muscles often work in antagonistic pairs. These are sets of two muscles that oppose each other: one pulls to move the joint one way, while the other relaxes to allow it.

In an antagonistic pair, the muscle that contracts to create the movement is called the agonist. The opposing muscle, which relaxes and lengthens, is the antagonist. When the movement reverses, their roles switch.

How antagonistic pairs function

1. The agonist contracts and shortens, pulling on its tendon to move the bone.
2. The antagonist relaxes and lengthens, allowing the joint to change position without resistance.
3. Roles reverse for the opposite movement, ensuring balanced control.

The role of fixator muscles in supporting movement

Fixator muscles (also called stabilisers) contract to hold parts of the body steady, preventing unwanted movement and supporting the agonist. They typically stabilise the origin point of the agonist - the attachment to the stationary bone - so the force is directed effectively.

For example, during elbow flexion (bending the arm), the deltoids and trapezius act as fixators to keep the shoulder stable. Similarly, for movements at the knee or hip, the abdominals serve as fixators to maintain core stability.

Specific antagonistic muscle pairs by joint

Different joints rely on specific antagonistic pairs to enable a range of movements.

Elbow joint antagonistic pairs

• Flexion - Biceps (agonist), triceps (antagonist)
• Extension - Triceps (agonist), biceps (antagonist)

Knee joint antagonistic pairs

• Flexion - Hamstrings (agonist), quadriceps (antagonist)
• Extension - Quadriceps (agonist), hamstrings (antagonist)

Shoulder joint antagonistic pairs

• Flexion - Front part of deltoid (agonist), back part of deltoid (antagonist)
• Extension - Back part of deltoid (agonist), front part of deltoid (antagonist)
• Adduction - Latissimus dorsi (agonist), middle part of deltoid (antagonist)
• Abduction - Middle part of deltoid (agonist), latissimus dorsi (antagonist)