Movement at joints
Movement at hinge joints
Hinge joints (the knee and elbow) allow two movements:
- bending a joint, so the angle between the bones decreases. Example: the knee flexes as a sprinter brings the leg forward; the elbow flexes when a weightlifter curls a dumbbell up.
- straightening a joint, so the angle between the bones increases. Example: the knee extends as a footballer kicks the ball; the elbows extend as a basketball player shoots.
Ball and socket joints can flex and extend too: the hip flexes as a hurdler lifts the leading leg.
Key terms
Movement at ball and socket joints
As well as flexion and extension, the shoulder and hip allow four more movements:
| Movement | What happens | Example |
|---|---|---|
| A bone turns around its own long axis | The shoulder in a tennis serve; the hip in a golf swing | |
| A limb moves away from the middle of the body | Arms and legs moving out in a star jump | |
| A limb moves towards the middle of the body | Legs squeezing together in a breaststroke kick | |
| A limb moves in a circle, so the end of it draws a circle | The arm in a cricket bowling action; arm circles in a warm-up |
Circumduction combines flexion, extension, abduction and adduction.
Remember
Abduction takes the limb away, like 'abduct'. Adduction adds it back to the body.
Key terms
Ligaments, cartilage and tendons
- join bone to bone. They hold the joint together and keep it stable, stopping it moving too far: the knee ligaments stop the knee twisting when a footballer changes direction.
- is a smooth, tough tissue covering the ends of the bones. It reduces friction and absorbs shock: it cushions the knees when a netball player lands.
- join muscle to bone, so when a muscle contracts it pulls the bone: the Achilles tendon joins the calf muscle to the heel, so a sprinter can push off the ground.
Common mistake
Don't mix up ligaments and tendons: ligaments link bone to bone; tendons tie muscle to bone.