2.3 Movement: joints
Summary: Without muscles and joints, we would all look like statues. Muscles move bones, and joints allow the skeleton to bend. Together, muscle and joint movement is called biomechanics. Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- describe the role of joints in movement
- describe the structure of a joint
- describe how to measure the force exerted (applied) by different muscles.
Think back
Key idea Joints help us move in different directions.
Key words muscle, joint, bone, biomechanics, ligament, cartilage, newton (N)
Without muscles and joints, we would all look like statues. Muscles move bones, and joints allow the skeleton to bend. Together, muscle and joint movement is called biomechanics.
What are joints?
Joints occur where two or more bones join together. Most joints have a range of movement. However, some bones in your skeleton are joined rigidly together and cannot move.
How do joints allow you to move?
Your joints need to be strong to hold your bones together. They also need to let your bones move. Different types of joint allow movement in different directions. Figure 1 shows a pivot joint.
Figure 1Pivot joints allow movement around a point. Your neck is a pivot joint. It allows you to turn your head from side to side.
Other types of joint include:
- hinge joints – for movement backwards and forwards. The knee and the elbow are examples of hinge joints.
- ball-and-socket joints – for movement in all directions. The hip and the shoulder are examples of ball-and-socket joints.
- fixed joints – do not allow any movement. The skull is an example of a fixed joint.
A Name four types of joint in the body.
What does a joint look like?
Most joints consist of two bones held together by ligaments. Figure 2 shows two different types of joint.
Figure 2Structure of a hip joint and a knee joint. Full text alternative to the content
If your bones moved against each other, they would rub, causing lots of pain. Eventually, the bone would wear away. To stop this happening, the ends of bones in a joint are covered with cartilage. This is a strong, smooth tissue. Fluid (liquid) in the joint keeps the cartilage slippery. This allows the bones to move without rubbing together.
B Name the tissue which holds bones together.
How can you measure muscle strength?
Different muscles in the body have different strengths. For example, arm muscles are much stronger than the muscles in your face that let you smile.
The strength of a muscle can be measured by how much force it exerts (applies). You can measure the strength of your muscles using a newton scale. The harder you push on the scale, the greater the force exerted. Force is measured in newtons (N).
C Give the unit of force.
You can use a newton scale to measure the strength of many different muscles. For example:
- To measure the strength of your triceps – push down as hard as you can on the scale.
- To measure the strength of your biceps – put the scale under the table and push up as hard as you can. Look at Figure 3 to see how this is done (ask another student to sit on the table so that it does not move).
- To measure the strength of your forearms – hold the scale in the air between your hands, and press your hands together as hard as you can without using your thumbs.
In each technique, read the force you exerted (in newtons) from the scale.
Figure 3How to measure the strength of your biceps.
Working scientifically Many people go to the gym and lift weights to improve the strength of their muscles. What are the risks of trying to lift the heaviest weights?
Stretch zone
- Copy and complete the sentences. Joints occur where two or more bones/muscles join together. Different types of joint allow movement/support in different directions. For example, ball-and-socket joints in the elbows/hips allow movement in all directions. Cartilage/Ligament covers the ends of the bones in joints to stop them rubbing together. Muscle strength is measured in metres/newtons.
- Describe how the structures in a joint prevent bones rubbing together.
Stretch zone
- The ankle joint allows forwards and backwards movement. Identify the type of joint in the ankle.Compare the movement of the ankle joint with the skull and the shoulder joints.