Where the ends of two or more bones meet, they form joints. Most of these joints are movable. They let your body bend and take up different positions. The bendiest joints include the shoulders, knees, hips and elbows. Hinge joints, like the elbow and knee, work like a door hinge. They allow up and down movement, but not from side to side. The ball and socket joints in the shoulder and hip allow a wider range of movements, including circular movement.

Inside a joint

In a movable joint, the ends of the bones are covered with a smooth, slippery substance called cartilage (or gristle). It stops the bones rubbing against each other and wearing away. Special fluid fills the space between the bones. It keeps the joint moist, allowing it to move without friction. Movable joints are held in place by straps called ligaments.

Hands and feet

Only the human animal can touch its thumb with the tip of every other finger. Your hands enable you to do a wide range of delicate tasks, such as typing on a keyboard, playing a violin or holding a pen while unscrewing the top. They are also strong enough to allow you to grip or flick with great power.

​​​​​​​Your feet must bear the weight of your body, allow you to walk or run, and keep you balanced upright. For this reason, the toe bones are broader and flatter than those in the fingers. Like some bridges, the foot has an arched shape. This is specially designed to support a large weight.