Types of muscle contraction: WACE Physical Education Studies Unit 3
“Describe concentric, eccentric, isometric and isokinetic contractions and identify examples of each in sporting movements”
A concentric contraction shortens the muscle as it produces force, an eccentric contraction lengthens the muscle while still under tension to control or brake a movement, an isometric contraction produces tension with no change in length, and an isokinetic contraction works at a constant speed through the range. WACE wants the muscle length change plus a clear sporting example for each.
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.
In a biceps curl the biceps works on both the way up and the way down. Lifting is concentric, lowering is eccentric. The muscle does not switch off and let gravity do the work on the way down; if it did, the weight would drop. Recognising that one muscle controls both directions, just with different contraction types, is a common exam discriminator.
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.
Two errors recur. First, students write that an isometric contraction means the muscle is not working because nothing moves; in fact it is generating high tension to resist movement. Second, students label ordinary gym lifts as isokinetic. Most free weight and machine exercises are isotonic, because the speed varies through the range. Reserve isokinetic for constant speed, variable resistance work such as specialised dynamometers or water based pulling.
Step 1: identify the muscle and the joint action
For a press-up, focus on the triceps at the elbow. In the lowering phase the elbow flexes; in the pushing phase the elbow extends.
Step 2: decide if the muscle is shortening, lengthening or holding
On the way down the triceps lengthens under tension to control the descent; on the way up it shortens to extend the elbow. If the body were held halfway with no movement, the triceps would be holding length.
Step 3: name the contraction type
Lowering is an eccentric contraction (lengthening under tension), pushing up is a concentric contraction (shortening under tension), and a paused hold is an isometric contraction (tension, no length change).
Step 4: justify with length and tension
State the length change and that the muscle stays under tension throughout, then add that most such free-body exercises are isotonic (variable speed), not isokinetic. Adding a second example of your own shows command of the concept.
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.
Exam-style questions
Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
WACE 2021-style6 marksFor the downward (lowering) and upward (lifting) phases of a barbell squat, identify the type of contraction occurring in the quadriceps in each phase, describe what happens to muscle length and tension, and give one reason eccentric work is linked to muscle soreness.Show worked answer →
A 6 mark answer needs both phases named with length/tension changes plus the soreness link.
- Lowering phase
- The quadriceps performs an eccentric contraction: the muscle lengthens while still under tension, acting as a brake to control the descent against gravity.
- Lifting phase
- The quadriceps performs a concentric contraction: the muscle shortens as it develops tension to overcome the load and extend the knee, driving the body up.
- Tension
- In both phases the muscle is under tension and actively working; the difference is whether it lengthens (eccentric) or shortens (concentric).
- Soreness link
- Eccentric contractions generate high tension while lengthening, causing more microscopic damage to muscle fibres, which is associated with delayed onset muscle soreness after unfamiliar exercise.
Markers reward eccentric on the way down, concentric on the way up, the correct length change under tension in each, and the eccentric-soreness link.
WACE 2023-style4 marksDistinguish between an isometric and an isokinetic contraction, giving one sporting or training example of each.Show worked answer →
A 4 mark distinguish answer needs both defined and exemplified.
- Isometric
- The muscle produces tension but does not change length and no visible movement occurs; it holds a position. Example: holding a plank or a gymnast holding a still position on the rings.
- Isokinetic
- The muscle works at a constant speed throughout the full range while the resistance varies to match the force the muscle can apply at each joint angle. It usually needs specialised equipment. Example: a constant-speed pull on an isokinetic dynamometer in rehabilitation, or the resisted pull in swimming where water adjusts to effort.
- Key contrast
- Isometric means no length change and no movement; isokinetic means movement at constant speed with variable resistance.
Markers reward the no-length-change definition with example, the constant-speed/variable-resistance definition with example, and a clear contrast.