Movement Analysis: Agonist and Antagonist Muscle Roles
Muscles can only pull, not push, so they work in opposing pairs across a joint to create movement in both directions.
Before you start
Make sure you're comfortable with these topics first:
Method
- Learn the definitions of agonist (the muscle that contracts to cause the movement) and antagonist (the opposing muscle that relaxes to allow the movement).
- Learn that the same muscle can be the agonist in one movement and the antagonist in the opposite movement at the same joint, so always identify the direction of movement first.
- Learn the three most commonly tested agonist-antagonist pairs: biceps brachii and triceps brachii at the elbow, quadriceps and hamstrings at the knee, gastrocnemius and tibialis anterior at the ankle.
- To identify the agonist for a given movement, ask which muscle's contraction would produce that exact joint action (e.g. which muscle shortens to cause knee extension).
- For 'explain' questions on muscle action, name the agonist, state that it contracts, name the antagonist, state that it relaxes, and name the joint action being produced.
- For an extended question analysing a sporting movement with multiple phases, work through the phases in order and identify the agonist and antagonist separately for each phase, since the roles will often swap.
Worked example
A weightlifter performs a biceps curl, lifting the weight up (elbow flexion) and then lowering it back down (elbow extension). Identify the agonist and antagonist during each phase of the movement.
- Identify the joint action in the lifting phase: elbow flexion, the angle at the elbow decreasing as the weight is raised.
- Identify the agonist for flexion: the biceps brachii contracts and shortens to pull the forearm upward, so it is the agonist during this phase.
- Identify the antagonist for flexion: the triceps brachii relaxes and lengthens to allow the movement, so it is the antagonist during this phase.
- Identify the joint action in the lowering phase: elbow extension, the angle at the elbow increasing as the weight is lowered back down.
- State the final answer: during flexion (lifting), the biceps brachii is the agonist and the triceps brachii is the antagonist; during extension (lowering), the roles reverse, with the triceps brachii as the agonist and the biceps brachii as the antagonist.
Practice questions
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Q1Define agonist.Show answer
Answer: The muscle that contracts and shortens to cause a movement (also called the prime mover).
Q2Define antagonist.Show answer
Answer: The muscle that relaxes and lengthens on the opposite side of the joint, to allow the movement to happen.
Q3Name the agonist during elbow flexion.Show answer
Answer: The biceps brachii.
Q4Name the agonist during knee extension.Show answer
Answer: The quadriceps.
Q5Name the muscle pair that acts as agonist and antagonist at the ankle.Show answer
Answer: The gastrocnemius and the tibialis anterior.
Q6During elbow extension, which muscle is the antagonist?Show answer
Answer: The biceps brachii.
Q7Explain why muscles need to work in agonist-antagonist pairs rather than alone.Show answer
Answer: Muscles can only pull, not push, so a joint needs an opposing muscle on the other side to reverse the movement and return the joint to its original position.
Exam-style questions
Written in the style of a GCSE Physical Education exam paper, with a full mark scheme.
State the antagonist muscle during knee extension.
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Explain the roles of the quadriceps and hamstrings during a knee flexion movement, such as bending the knee to bring the heel towards the buttocks.
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Analyse the agonist and antagonist muscle roles at the knee during the upward (concentric) and downward (eccentric) phases of a squat.
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See real GCSE Physical Education past-paper questions, with official mark schemes →
Free printable worksheet
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