How do muscles work in pairs to create movement, and what are the different types of muscle contraction?
The major muscles of the body, how muscles work as antagonistic pairs, the types of muscle contraction (concentric, eccentric, isometric), and the types of muscle fibre.
A focused answer to the WJEC GCSE PE topic on the muscular system, covering the major muscles, how muscles work as antagonistic pairs (agonist and antagonist), the types of muscle contraction (concentric, eccentric and isometric) and the two types of muscle fibre.
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What this dot point is asking
WJEC wants you to name the major muscles, explain how muscles work as antagonistic pairs, describe the types of muscle contraction, and outline the types of muscle fibre.
The major muscles
Know the location and a sporting role for the main muscles.
- Biceps (front of upper arm): flexes the elbow.
- Triceps (back of upper arm): extends the elbow.
- Deltoids (shoulder): move the arm at the shoulder.
- Pectorals (chest): adduct the arm, used in a press-up or throw.
- Abdominals (stomach): flex the trunk, used in a sit-up.
- Quadriceps (front of thigh): extend the knee, used in kicking and jumping.
- Hamstrings (back of thigh): flex the knee, used in running.
- Gastrocnemius (calf): plantarflexes the ankle, used in pointing the toes and pushing off.
- Gluteals (buttocks): extend the hip, used in running and jumping.
Antagonistic muscle pairs
In a biceps curl:
- Flexion (lifting): the biceps is the agonist (contracts); the triceps is the antagonist (relaxes).
- Extension (lowering): the roles swap, so the triceps becomes the agonist and the biceps relaxes.
Other pairs include the quadriceps and hamstrings at the knee, and the abdominals and back muscles at the trunk.
Types of muscle contraction
Types of muscle fibre
There are two main fibre types, and a performer's mix affects the sports they are suited to.
- Slow-twitch (type I): contract slowly, resist fatigue, suited to endurance events such as a marathon.
- Fast-twitch (type II): contract quickly and powerfully but tire fast, suited to power and speed events such as sprinting and jumping.
Why this matters
The muscular system works with the skeletal system: muscles pull on bones at the joints to create the movements analysed in the movement analysis topic. Muscle fibre type and contraction also connect to the components of fitness and to the long-term effects of training, such as muscle hypertrophy.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain how an antagonistic muscle pair produces movement, using the biceps and triceps as an example.Show worked answer →
A 4-mark question: reward the idea of agonist and antagonist working together, with the biceps and triceps example.
Muscles can only pull, not push, so they work in antagonistic pairs where one muscle contracts as the other relaxes. The muscle that contracts to cause the movement is the agonist (prime mover); the muscle that relaxes is the antagonist.
To bend the arm (flexion at the elbow), the biceps contracts as the agonist while the triceps relaxes as the antagonist. To straighten the arm (extension), the roles swap: the triceps contracts as the agonist while the biceps relaxes. Markers reward the contract or relax pairing and the correct agonist for each movement.
WJEC style6 marksDescribe the three types of muscle contraction and give a sporting example of each.Show worked answer →
A 6-mark question: two marks for each type (description plus example).
A concentric contraction is when the muscle shortens under tension as it contracts, for example the biceps shortening on the way up of a biceps curl. An eccentric contraction is when the muscle lengthens under tension while still contracting, usually to control a movement against gravity, for example the biceps lengthening as you lower the weight in a biceps curl, or the quadriceps controlling the landing from a jump. An isometric contraction is when the muscle contracts but stays the same length, producing no movement, for example holding a plank or a gymnast holding a crucifix on the rings.
A top answer correctly describes the length change (or lack of it) for each type and gives a clear sporting example of each.
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Sources & how we know this
- WJEC GCSE Physical Education specification (from 2016) — WJEC (2016)