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This lesson covers antagonistic muscle action as required by the AQA GCSE PE specification (3.1.1.1). You need to understand that muscles can only pull (contract) — they cannot push. Because of this, muscles work in pairs to produce movement at a joint. When one muscle contracts, the opposite muscle relaxes. This is called antagonistic muscle action.
A single muscle can only produce movement in one direction. To move a joint and then return it to its original position, you need two muscles working on opposite sides of the joint.
This is why muscles always work in antagonistic pairs.
flowchart LR
A["Muscle A Contracts"] --> B["Produces Movement in Direction 1"]
B --> C["Muscle B Relaxes to Allow Movement"]
D["Muscle B Contracts"] --> E["Produces Movement in Direction 2"]
E --> F["Muscle A Relaxes to Allow Movement"]
style A fill:#4a90d9,color:#fff
style D fill:#e67e22,color:#fff
style B fill:#27ae60,color:#fff
style E fill:#27ae60,color:#fff
| Term | Definition |
|---|---|
| Agonist (prime mover) | The muscle that contracts to produce the movement |
| Antagonist | The muscle that relaxes to allow the movement to happen |
| Antagonistic pair | Two muscles that work on opposite sides of a joint, taking turns as agonist and antagonist |
Exam Tip: The terms "agonist" and "prime mover" mean the same thing. Either term can be used in the exam. The agonist is always the muscle that is contracting to produce the current movement.
The biceps and triceps are the classic antagonistic pair at the elbow joint.
| Movement | Agonist | Antagonist | Sporting Example |
|---|---|---|---|
| Flexion at elbow | Biceps | Triceps | Bicep curl (upward phase) |
| Extension at elbow | Triceps | Biceps | Throwing a javelin |
The quadriceps and hamstrings are the antagonistic pair at the knee joint.
| Movement | Agonist | Antagonist | Sporting Example |
|---|---|---|---|
| Extension at knee | Quadriceps | Hamstrings | Kicking a football |
| Flexion at knee | Hamstrings | Quadriceps | Bending legs for a squat |
The hip flexors and gluteals are the antagonistic pair at the hip joint.
| Movement | Agonist | Antagonist | Sporting Example |
|---|---|---|---|
| Flexion at hip | Hip flexors | Gluteals | Lifting knee in running |
| Extension at hip | Gluteals | Hip flexors | Sprinting (drive phase) |
The deltoid and latissimus dorsi are the antagonistic pair for abduction and adduction at the shoulder joint.
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