How do the different types of muscle contraction differ, and when is each one used in sport?
Describe concentric, eccentric, isometric and isokinetic contractions and identify examples of each in sporting movements
A focused answer to the WACE Year 12 Physical Education Studies Unit 3 content on types of muscle contraction. Isotonic concentric and eccentric contractions, isometric contractions and isokinetic contractions, what each one does to muscle length and tension, and clear sporting examples of when each occurs.
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What this dot point is asking
The key to this content is describing what happens to muscle length and tension in each contraction, then attaching a sporting example. Examiners often show a phase of a movement and ask which contraction is occurring in a named muscle.
Isotonic contractions
An isotonic contraction is one where the muscle changes length while moving a load. It has two directions.
A concentric contraction is when the muscle shortens as it develops tension and overcomes the resistance. The upward phase of a biceps curl is concentric for the biceps, as is the push up phase of a squat for the quadriceps. This is the contraction people usually picture when they think of a muscle working.
An eccentric contraction is when the muscle lengthens while still under tension, acting as a brake to control the movement against gravity or momentum. Lowering the dumbbell in a biceps curl is eccentric for the biceps, and the controlled descent into a squat is eccentric for the quadriceps. Eccentric contractions absorb force and are strongly linked to muscle soreness after unfamiliar exercise.
Isometric contractions
An isometric contraction produces tension but the muscle length does not change and no visible movement occurs. It is used to hold a position or to stabilise a joint. Holding a plank, gripping a barbell at the top of a deadlift, or a gymnast holding a crucifix on the rings are all isometric. The muscle is clearly working hard, yet the joint angle stays fixed.
Isokinetic contractions
An isokinetic contraction is one performed at a constant speed throughout the full range of movement, with the resistance varying to match the force the muscle can apply at each joint angle. True isokinetic work needs specialised machines that adjust the load, so it is used mainly in rehabilitation and testing. The closest everyday example is the pulling phase in swimming or rowing where the resistance of the water adjusts to the effort, keeping the speed of the movement fairly constant.
How this maps to the exam
A stimulus may show one frame of a movement and ask you to name the contraction in a stated muscle and justify it. Decide whether the muscle is shortening, lengthening or holding, then name concentric, eccentric or isometric and give the length change. Adding a second example of your own shows command of the concept.