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# Muscle Contractions Allowing Movements Muscles contract and relax to allow for movement. When a muscle contracts, it becomes shorter and thicker. When a muscle relaxes, it becomes longer and thinner. Two muscles work opposite to one another to allow for movement. For example, during the flexion...

# Muscle Contractions Allowing Movements Muscles contract and relax to allow for movement. When a muscle contracts, it becomes shorter and thicker. When a muscle relaxes, it becomes longer and thinner. Two muscles work opposite to one another to allow for movement. For example, during the flexion of the forearm, the biceps contracts while the triceps relaxes. However, during the extension of the forearm, the biceps relaxes while the triceps contracts. **Diagram Description:** The diagram shows a human arm with the biceps and triceps muscles labeled. The diagram shows two positions of the arm: one where the forearm is bent (flexion), and one where the forearm is straight (extension). The biceps and triceps muscles are shown in different states of contraction and relaxation in each position. An arrow indicates the direction of the movement. A person playing tennis is shown in the background.