Synovial joints
- A joint is where two or more bones meet. Most joints used in sport are synovial joints, which allow a lot of movement.
- The joint capsule surrounds the joint and holds it together.
- The synovial membrane lines the capsule and releases synovial fluid, which lubricates the joint and reduces friction.
- Cartilage covers the ends of the bones, stopping them rubbing together and absorbing shock.
- Bursae are small fluid-filled sacs that reduce friction where tendons rub over bones.
- Ligaments join bone to bone and keep the joint stable.
Types of joint
- Ball and socket joints (shoulder and hip) allow movement in every direction, including rotation.
- Hinge joints (elbow, knee and ankle) allow flexion and extension, like a door.
- Pivot joints (the neck, between the atlas and axis vertebrae) allow rotation.
- Condyloid joints (the wrist) allow flexion, extension, abduction and adduction but not full rotation.
Movements at joints
- Flexion: the angle at a joint gets smaller, such as bending the knee.
- Extension: the angle at a joint gets bigger, such as straightening the arm.
- Abduction: movement away from the midline of the body, such as raising the arm sideways.
- Adduction: movement towards the midline, such as bringing the arm back down.
- Rotation: a bone turns about its own axis, such as the shoulder in a tennis serve.
- Circumduction: a circular movement at a ball and socket joint, such as bowling in cricket.
- Plantar flexion: pointing the toes (the angle at the ankle increases). Dorsiflexion: pulling the toes up towards the shin.
Examples in sport
- Kicking a football: the knee extends at the moment of contact.
- A chest pass: the elbows extend to push the ball away.
- Jumping for a header: plantar flexion at the ankles helps push off.
Key terms
- Synovial joint
- A freely movable joint with a capsule and synovial fluid.
- Synovial fluid
- Liquid that lubricates a joint and reduces friction.
- Cartilage
- Smooth tissue on the ends of bones that absorbs shock.
- Ligament
- Tough tissue that joins bone to bone.
- Bursa
- A fluid-filled sac that reduces friction at a joint.
- Flexion
- A movement that decreases the angle at a joint.
- Extension
- A movement that increases the angle at a joint.
- Abduction
- Movement away from the midline of the body.
- Adduction
- Movement towards the midline of the body.