Types of Muscle Contraction

This lesson covers the types of muscle contraction as required by the OCR GCSE PE specification (J587). You need to understand the difference between isometric and isotonic contractions, and within isotonic contractions, the difference between concentric and eccentric contractions. You must be able to define each type and apply them to sporting examples.

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Overview of Muscle Contraction Types

When a muscle is activated (receives a signal from the nervous system), it generates force. However, the way the muscle changes length — or whether it changes length at all — depends on the type of contraction occurring.

graph TD
    A["Types of Muscle Contraction"] --> B["Isotonic<br>(muscle changes length)"]
    A --> C["Isometric<br>(muscle stays the same length)"]
    B --> D["Concentric<br>(muscle shortens)"]
    B --> E["Eccentric<br>(muscle lengthens)"]

    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:#e74c3c,color:#fff

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Isotonic Contractions

An isotonic contraction is one in which the muscle changes length while generating force. The word "isotonic" comes from the Greek words for "equal tension" — the tension in the muscle remains roughly constant while the muscle changes length.

There are two types of isotonic contraction:

1. Concentric Contraction

A concentric contraction occurs when the muscle shortens while generating force. This is the most commonly understood type of contraction — the muscle contracts and gets shorter, pulling the bone and producing movement.

Feature	Detail
Definition	The muscle shortens while generating force
What happens	The muscle fibres actively shorten, pulling the bones closer together
Role	The muscle is acting as the agonist (prime mover)
Result	Movement occurs in the direction of the muscle's pull

Sporting Examples:

Action	Muscle	Explanation
Bicep curl (lifting phase)	Biceps	The biceps shortens as the weight is lifted, producing flexion at the elbow
Kicking a football (striking phase)	Quadriceps	The quadriceps shortens to extend the knee and strike the ball
Jumping (take-off)	Gastrocnemius, quadriceps, gluteals	These muscles shorten to extend the legs and push the body upward
Press-up (pushing up)	Triceps	The triceps shortens to extend the elbow and push the body upward
Sprinting (push-off phase)	Gastrocnemius, gluteals	These muscles shorten to drive the body forward

2. Eccentric Contraction

An eccentric contraction occurs when the muscle lengthens while still generating force. The muscle is under tension but is being stretched by an external force (such as gravity or the weight being lowered). It acts as a brake, controlling the speed of the movement.

Feature	Detail
Definition	The muscle lengthens while generating force
What happens	The muscle fibres generate tension but are stretched by an external force
Role	The muscle is controlling the movement (often acting as a brake)
Result	Controlled, smooth lowering or decelerating movement

Sporting Examples:

Action	Muscle	Explanation
Bicep curl (lowering phase)	Biceps	The biceps lengthens under tension as the weight is slowly lowered
Landing from a jump	Quadriceps	The quadriceps lengthens under tension to control the bending of the knee on landing
Running downhill	Quadriceps	The quadriceps eccentrically controls knee flexion to prevent collapse
Lowering into a squat	Quadriceps, gluteals	These muscles lengthen under tension to control the descent
Press-up (lowering phase)	Triceps	The triceps lengthens under tension as the body is lowered to the ground

Exam Tip: Think of eccentric contractions as the "braking" contraction. The muscle is still working (generating tension) but it is getting LONGER, not shorter. It is controlling the speed of the movement rather than producing it. A good way to remember: eccentric = elongating.

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Isometric Contractions

An isometric contraction occurs when the muscle generates force but does not change length. There is no movement at the joint — the muscle is working to hold a position or resist a force.

The word "isometric" comes from the Greek words for "equal measure" — the length of the muscle remains the same even though it is generating force.

Feature	Detail
Definition	The muscle generates force without changing length
What happens	The muscle fibres generate tension but no movement occurs
Role	Holding a position or resisting a force
Result	No visible movement at the joint

Sporting Examples: