How do muscles work in antagonistic pairs, and what are the types of muscle and muscle contraction used in sport?
The major muscles of the body, how muscles work in antagonistic pairs as agonist and antagonist, the types of muscle (voluntary, involuntary and cardiac), and the types of contraction (isotonic and isometric) applied to physical activity.
A focused CCEA GCSE Physical Education answer on the muscular system, covering the major muscles, antagonistic muscle pairs and the roles of agonist and antagonist, the types of muscle, and isotonic and isometric contraction in sport.
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What this dot point is asking
CCEA wants you to name the major muscles, explain how muscles work in antagonistic pairs as agonist and antagonist, know the three types of muscle, and describe isotonic and isometric contraction, all applied to sporting movement. Antagonistic pairs and the two types of contraction are favourite CCEA questions, so learn the worked biceps curl below.
The major muscles
Muscles are attached to bones by tendons. When a muscle contracts it shortens and pulls on the bone, creating movement at the joint. Muscles can only pull, not push, which is why they have to work in pairs.
Antagonistic muscle pairs
The key pairs to learn are:
| Joint | Antagonistic pair | When flexing | When extending |
|---|---|---|---|
| Elbow | Biceps and triceps | Biceps agonist | Triceps agonist |
| Knee | Quadriceps and hamstrings | Hamstrings agonist | Quadriceps agonist |
Types of muscle
Isotonic and isometric contraction
Examples in context
Example 1. The press-up. Pushing up from the floor, the triceps and pectorals contract as the agonists to straighten the arms, while their antagonists relax. Lowering down, the roles reverse so the movement stays controlled. If a gymnast holds the press-up position halfway, the muscles contract isometrically: they generate tension to hold the body still without any change in length. CCEA likes you to identify both the pair and the type of contraction in a named action.
Example 2. Why cardiac muscle is special. The heart is made of cardiac muscle, which contracts continuously throughout life without tiring and is not under conscious control. During exercise it contracts faster and harder to pump more blood to the working muscles. Because it never rests, a fit performer's cardiac muscle becomes stronger with training, which links the muscular system to the cardiovascular topic and to the long-term effects of exercise.
Try this
Q1. Name the antagonistic pair of muscles that move the lower leg at the knee. [2 marks]
- Cue. The quadriceps and the hamstrings.
Q2. State whether holding a plank is an isotonic or isometric contraction and explain why. [2 marks]
- Cue. Isometric, because the muscles contract but do not change length and there is no movement.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 2019 Paper 14 marksExplain the action of the antagonistic muscle pair as a person performs a biceps curl.Show worked answer →
Four marks for naming the muscles and explaining the antagonistic action through the lift and lower.
The muscles involved in the biceps curl are the biceps and the triceps, an antagonistic pair at the elbow.
As the weight is lifted (the elbow flexes), the biceps is the agonist (prime mover); it contracts and shortens to pull the forearm up.
At the same time the triceps is the antagonist; it relaxes and lengthens to allow the movement to happen.
As the weight is lowered (the elbow extends), the roles swap: the triceps becomes the agonist and the biceps relaxes.
Markers reward the pair named, the contracting agonist, the relaxing antagonist, and the swap of roles on lowering.
CCEA 2022 Paper 13 marksFigure 5 shows the quadriceps and hamstrings working as an antagonistic pair producing isotonic contraction at the knee. Explain what is meant by isotonic contraction and identify the agonist as the knee straightens.Show worked answer →
Three marks: one for defining isotonic, one for the muscle changing length, one for identifying the agonist.
Isotonic contraction is when the muscle changes length as it contracts, producing movement at the joint.
During the movement the muscle shortens or lengthens under tension, so the joint angle changes, as the leg straightens or bends.
As the knee straightens (extends), the quadriceps is the agonist (prime mover); it contracts to extend the leg while the hamstrings relax.
Markers reward isotonic defined as a contraction with a change in length producing movement, and the quadriceps named as the agonist on extension.
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