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Muscles and Joints Investigation

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Muscles and Joints Investigation

How do muscles create movement at a joint? Use the model, data and evidence on this sheet to investigate. You will need a timer, a light object such as a pencil case, and a partner if available. Do not use heavy weights or continue if you feel pain. Stop and rest if your arm feels uncomfortable.

Build a movement model

A forearm moves around the elbow, a hinge joint. The biceps and triceps work as an antagonistic pair: when one contracts, the other relaxes. Try bending and straightening your elbow without adding a load, then with a light object in your hand.

1.During elbow flexion (bending), which muscle contracts most directly to pull the forearm upwards?

Biceps
Triceps
Both relax

2.Match each term to the best description: flexion; extension; contraction; antagonistic pair.

Flexion
Extension
Contraction
Antagonistic pair

Two muscles that produce opposite actions at a joint
Bending a joint
Straightening a joint
A muscle develops tension and usually shortens

3.Explain why a muscle can pull a bone but cannot push it back to its starting position. Use the elbow example.

Test and collect evidence

Investigation question: Does holding a light object with the elbow bent change how long a person can maintain the position? Method: Sit safely with your upper arm close to your side. First hold your forearm horizontally with no object; time up to 60 seconds or until you choose to stop. Rest for two minutes. Repeat holding a light object. Keep the elbow angle and posture as similar as possible. Record actual results; do not copy the example table as data.

Trial

Load

Time (s) and observations

No object

________

Light object

________

4.Identify one variable you kept the same to make this test fair, and explain why it matters.

5.Which statement best describes the main limitation of using only one timed trial for each condition?

A single result may be affected by chance or inconsistent effort, so it may not represent a reliable pattern.
It proves that the object caused every difference.
It removes the need to control variables.

6.Write a conclusion using your own results: compare the two times, state whether your evidence supports the idea that the load affected holding time, and include one reason for uncertainty. If your times were similar, say so rather than forcing a difference.

7.During a sustained hold, muscles may remain active even when the joint barely moves. What is this type of muscle action called, and what observation could indicate effort?

Apply your understanding

A joint model is useful, but it simplifies a living system. Think about what it can and cannot represent.

8.The shoulder is a ball-and-socket joint, while the elbow is a hinge joint. Give one movement the shoulder can make that the elbow cannot, and explain how joint shape helps.

9.Choose one limitation of a simple cardboard or lever joint model and suggest an improvement that would make it represent a real joint or muscle action more accurately.