Fig. 1 shows the upper arm of a performer lifting a weight. The diagram shows two muscles working together to produce movement at the elbow. (a) Name the mu...
Question 1 Report
Fig. 1 shows the upper arm of a performer lifting a weight. The diagram shows two muscles working together to produce movement at the elbow.
(a) Name the muscle that is contracting to produce the upward movement of the forearm. [1]
(b) State the role of the other muscle shown in the diagram during this movement. [1]
(c) Explain why muscles must work in pairs to create movement at a joint. [1]
Answer Details
(a) Muscle producing the upward movement
The muscle contracting to lift the forearm is the biceps. It is the agonist (prime mover) for elbow flexion, located on the front of the upper arm. When it shortens, it pulls the forearm upward. [1]
(b) Role of the other muscle
The triceps acts as the antagonist. It relaxes and lengthens to allow the biceps to produce the bending movement at the elbow. Without this coordinated relaxation, the movement would be opposed and could not occur smoothly. [1]
(c) Why muscles must work in pairs
Muscles can only pull (contract) - they cannot push. Therefore, once a muscle has contracted to produce a movement in one direction, a second muscle on the opposite side of the joint is needed to contract and produce the reverse movement. For example, the biceps bends the elbow, but it cannot straighten it again; the triceps must contract to extend the elbow back. This is why muscles work in antagonistic pairs. [1]
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