The skeletal system

A joint is a place where two or more bones meet and is also called an articulation.

Synovial joints (freely movable joints) allow us the free movement to perform skills and techniques during physical activity.

Synovial joints have synovial fluid in the joint cavity that lubricates or ‘oils’ the joint so it moves smoothly. Synovial fluid is made by the synovial membrane.

In synovial joints, the ends of the bones are covered with cartilage(called articular cartilage) which cushions the joint and prevents friction and wear and tear between the bone ends. Cartilage is a soft, spongy connective tissue. The articular capsule prevents wear and tear on the bones.

The bones in a synovial joint are connected by ligaments, which:

• are a type of connective tissue and are tough, fibrous and slightly elastic
• connect bone to bone and help keep the joint together
• stabilise the joints during movement and prevent dislocation by restricting actions outside the normal joint range
• can absorb shock because of their elasticity, which protects the joint
• help maintain correct posture and movement

The movement at a synovial joint is caused by the muscles attached across the joint. Muscles are attached to bone by tendons. Tendons are very strong, inelastic connective tissues that allow a muscle to pull on a bone to move it.

The main features of a synovial joint

Four of the synovial joint types are responsible for a range of sporting techniques.

1. Hinge – these can be found in the elbow, knee and ankle. Hinge joints are like the hinges on a door, and allow you to move the elbow and knee in only one direction. They allow flexion and extension of a joint. At the ankle, different terms are used. When the toes are pointed downwards, it is plantar flexion and when the toes are pointed upwards it is dorsiflexion.
2. Ball and socket – these types of joint can be found at the shoulder and hip and allow movement in almost every direction. A ball and socket joint is made up of a round end of one bone that fits into a small cup-like area of another bone.
3. Pivot – this joint can be found in the neck between the top two vertebrae. It allows only rotational movement such as moving your head from side to side as if you were saying ‘no’.
4. Condyloid – this type of joint is found at the wrist. It allows you to flex and extend the joint, and move it from side to side.

 

Four important synovial joints

Four important synovial joints used in most sporting actions are the elbow and shoulder joints in the arm, and the knee and hip joints in the leg.

The elbow and knee joints are both hinge joints. A hinge joint is a type of synovial joint that works like the hinge on a door, allowing bending and straightening only.

The shoulder and hip joints are both ball and socket joints. A ball and socket joint is a type of synovial joint that allows movement in almost every direction. A ball and socket joint is made up of a round end of one bone that fits into a small cup-like area of another bone.

Elbow joint

• Hinge joint.
• Articulating bones are humerus, radius and ulna.
• Allows bending (flexion) and straightening (extension).
• Muscles which move the elbow are biceps and triceps.

The different components of the elbow joint that allow a hinge action

Knee joint

• Hinge joint.
• Articulating bones are femur and tibia (the patella is not classed as part of the joint, nor is the fibula).
• Allows bending (flexion) and straightening (extension).
• Muscles which move the knee are quadriceps and hamstrings.

The different components of the knee joint

Hip joint

• Ball and socket joint
• Articulating bones are pelvis and femur (head of femur is ‘ball’ and cup in pelvis is ‘socket’)
• Allows a large range of movement in all directions
• Many muscles are used to move the hip joint, including the gluteals

The different components of the hip joint

Shoulder joint

• Ball and socket joint.
• Articulating bones are humerus and scapula (the clavicle is not part of the shoulder joint).
• Allows a great range of movement in all directions.
• Many muscles are used to move the shoulder joint, including the deltoid, trapezius and latissimus dorsi.

The different components of the shoulder joint

Types of joint movement

The different types of movement that are permitted at each joint are described below.

Flexion – bending a joint. This occurs when the angle of a joint decreases. For example, the elbow flexes when performing a biceps curl.

Extension – straightening a joint. This occurs when the angle of a joint increases, for example, at the elbow when putting a shot.

Abduction – movement away from the midline of the body. This occurs at the hip and shoulder joints during a jumping jack movement.

Adduction – movement towards the midline of the body. This occurs at the hip and shoulder, returning the arms and legs back to their original position from a jumping jack movement.

Circumduction – this is where the limb moves in a circle. This occurs at the shoulder joint during an overarm tennis serve.

Rotation – this is where the limb moves in a circular movement around a fixed joint towards or away from the midline of the body. This occurs in the hip in golf while performing a drive shot.

Plantar flexion – pointing the toes – this movement only occurs at the ankle, for example, pointing the toes in ballet.

Dorsiflexion – the foot moves towards the shin as if you are pulling your toes up. This movement only occurs at the ankle.

The table summarises the body locations and types of movements associated with each type of joint.

Type of joint	Body location	Types of movement
Ball and socket	Hip, shoulder	Flexion/extension, rotation, abduction, adduction, circumduction
Hinge	Knee, elbow	Flexion/extension
Pivot	Neck	Rotation
Condyloid	Wrist	Flexion/extension, abduction, adduction, circumduction

Muscular-skeletal system

The muscular system works in conjunction with the skeleton to produce movement of the limbs and body.

Ligaments and tendons are two main types of connective tissues that help the muscular-skeletal system produce movements.

Ligaments:

• attach bone to bone
• act to give stability to joints
• are tough, white and inelastic

Tendons:

• attach muscle to bone
• carry the force from muscle contraction to the bone
• are tough, greyish and inelastic

The muscles contract to pull on the bones to produce movements. Joints are able to move in a variety of directions to allow us to perform a range of sporting movements.

An analysis of a netball shot shows how the muscular-skeletal system works together to produce this throw.

	Joint	Type of movement	Bones	Muscles	Muscle contraction
Phase 1	Elbow	Flexion	Humerus, radius, ulna	Biceps, triceps	Concentric
Phase 2	Elbow	Extension	Humerus, radius, ulna	Triceps, biceps	Concentric

Bibliography: BBC – Education

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