You are viewing a free preview of this lesson.
Subscribe to unlock all 10 lessons in this course and every other course on LearningBro.
This lesson covers the types of muscle contraction as required by the AQA GCSE PE specification (3.1.1.1): isometric contraction and isotonic contraction (which is subdivided into concentric and eccentric contraction). You need to know the definition of each type, understand how they differ, and apply them to sporting examples.
When a muscle is activated (receives a signal from the nervous system), it generates tension. However, the result of that tension depends on the forces acting on the muscle. This gives us two main categories:
| Type of Contraction | What Happens | Does the Muscle Change Length? | Does Movement Occur? |
|---|---|---|---|
| Isotonic | The muscle changes length while generating tension | Yes | Yes |
| Isometric | The muscle generates tension but does NOT change length | No | No |
graph TD
A["Types of Muscle Contraction"] --> B["Isotonic"]
A --> C["Isometric"]
B --> D["Concentric"]
B --> E["Eccentric"]
D --> F["Muscle shortens"]
E --> G["Muscle lengthens under tension"]
C --> H["Muscle stays the same length"]
style A fill:#4a90d9,color:#fff
style B fill:#e67e22,color:#fff
style C fill:#27ae60,color:#fff
style D fill:#9b59b6,color:#fff
style E fill:#9b59b6,color:#fff
Exam Tip: The prefix "iso" means "same" and "tonic" means "tension." So "isotonic" means the tension remains roughly the same while the length changes. "Isometric" uses "metric" (meaning "measure/length"), so "isometric" means the length stays the same while tension is generated.
Isotonic contraction occurs when a muscle changes length while generating force, resulting in movement at a joint. There are two subtypes:
Definition: A concentric contraction occurs when the muscle shortens while generating force. The muscle contracts and gets shorter, pulling the bone and producing movement.
This is the type of contraction most people think of when they hear the word "contraction."
| Sporting Action | Muscle | Joint | Movement Produced |
|---|---|---|---|
| Upward phase of a bicep curl | Biceps | Elbow | Flexion — biceps shortens |
| Kicking a football (follow-through) | Quadriceps | Knee | Extension — quadriceps shortens |
| Jumping (take-off phase) | Gluteals, quadriceps, gastrocnemius | Hip, knee, ankle | Extension / plantarflexion |
| Push-up (upward phase) | Triceps | Elbow | Extension — triceps shortens |
| Sprint start (driving off blocks) | Quadriceps, gluteals | Knee, hip | Extension |
| Throwing a ball (release phase) | Triceps | Elbow | Extension — triceps shortens |
Exam Tip: In a concentric contraction, the muscle is the agonist and it is shortening. The movement goes in the direction of the pull.
Definition: An eccentric contraction occurs when the muscle lengthens while still generating force. The muscle is under tension but is being stretched because the external force (e.g., gravity, an opponent, the weight of a limb) is greater than the force the muscle is producing.
This is often described as a "controlled lengthening" or "braking" action.
| Sporting Action | Muscle | Joint | What Is Happening |
|---|---|---|---|
| Downward phase of a bicep curl | Biceps | Elbow | Biceps lengthens under tension to control the lowering of the weight |
| Landing from a jump | Quadriceps | Knee | Quadriceps lengthens to control the bending of the knee on landing |
| Lowering into a squat | Quadriceps, gluteals | Knee, hip | Muscles lengthen to control the descent |
| The backswing before kicking a ball | Quadriceps | Knee | Quadriceps lengthens eccentrically as the knee flexes |
| Walking downhill | Quadriceps | Knee | Quadriceps controls the bending of the knee as the body descends |
| Decelerating after a sprint | Hamstrings, quadriceps | Knee, hip | Muscles lengthen to slow the body down |
Exam Tip: Eccentric contractions are the ones students find hardest to understand. The key point is that the muscle is still working (it is under tension) but it is getting longer, not shorter. Think of it as the muscle acting like a brake — controlling and slowing down a movement rather than producing it.
The bicep curl is the perfect example to illustrate both types of isotonic contraction:
| Phase | Direction | Muscle Action | Type of Contraction |
|---|---|---|---|
| Upward phase (lifting the weight) | Weight moves up | Biceps shortens to lift the weight | Concentric |
| Downward phase (lowering the weight) | Weight moves down | Biceps lengthens to control the lowering | Eccentric |
Subscribe to continue reading
Get full access to this lesson and all 10 lessons in this course.