How do muscles produce movement, and how do the fibre types and contractions suit different sports?
The muscular system: types of muscle, the main skeletal muscles, antagonistic muscle pairs and types of contraction, slow and fast twitch muscle fibres, and the effects of exercise on muscle.
A focused CCEA A2 Sports Science answer on the muscular system, covering the types of muscle, antagonistic pairs and types of contraction, slow and fast twitch fibre types and their suitability for different sports, and the effects of exercise on muscle.
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What this dot point is asking
CCEA wants you to know the types of muscle, how muscles produce movement in antagonistic pairs, the types of contraction, the two main muscle fibre types and the sports they suit, and how exercise affects muscle. The muscular system, working with the skeleton, generates all the force and movement of sport.
Types of muscle and antagonistic pairs
Skeletal muscles can only pull, never push, so they are arranged in antagonistic pairs. In any movement, the muscle that contracts to produce the action is the agonist (prime mover) and its relaxing partner is the antagonist. At the elbow, the biceps and triceps form such a pair: the biceps flexes the joint and the triceps extends it, swapping agonist and antagonist roles between the two phases.
Types of contraction
Recognising the type of contraction is needed to analyse movement: lifting a weight is concentric, lowering it under control is eccentric, and holding a static position is isometric.
Muscle fibre types and the effects of exercise
The body has two main fibre types. Slow twitch (type I) fibres contract slowly, produce less force and are very resistant to fatigue, with a rich blood supply and many mitochondria for aerobic energy; they suit endurance events. Fast twitch (type II) fibres contract quickly and produce large forces but fatigue rapidly, relying on anaerobic energy; they suit explosive events such as sprinting and weightlifting. Most people have a mix, with the proportion partly inherited. Exercise causes adaptation: resistance training produces muscle hypertrophy (larger, stronger fibres), while endurance training improves the muscles' aerobic capacity (more mitochondria and myoglobin and better fatigue resistance).
Examples in context
Example 1. Fibre type and the elite athlete. Elite marathon runners typically have a very high proportion of slow twitch fibres, which resist fatigue and sustain a steady pace for hours, whereas elite sprinters have a high proportion of fast twitch fibres, which contract quickly and generate the explosive force needed over ten seconds. This largely inherited difference is one reason athletes specialise: the fibre profile that makes a great sprinter is almost the opposite of the one that makes a great marathon runner.
Example 2. Eccentric contractions and muscle soreness. The eccentric (lengthening) phase of exercise, such as running downhill or lowering heavy weights, places particular stress on the muscle fibres and is strongly linked to delayed-onset muscle soreness felt a day or two later. Coaches use this knowledge to build up eccentric loading gradually so the muscles adapt without excessive soreness, which connects the type of contraction to practical training and injury management.
Try this
Q1. State the agonist and antagonist when the elbow extends to straighten the arm. [2 marks]
- Cue. The triceps is the agonist (contracts); the biceps is the antagonist (relaxes).
Q2. State which fibre type suits a 100 metre sprinter and give two reasons. [3 marks]
- Cue. Fast twitch (type II): they contract quickly and generate large forces, suiting a short, explosive event (though they fatigue quickly).
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 A2 20186 marksExplain how an antagonistic muscle pair produces movement at the elbow, using the biceps and triceps as your example.Show worked answer →
The marks come from the roles of agonist and antagonist and a worked example of each phase.
Muscles can only pull, not push, so they work in antagonistic pairs in which one muscle contracts while its partner relaxes. The muscle that contracts to produce the movement is the agonist (prime mover); the muscle that relaxes is the antagonist.
Flexing the elbow (the upward phase of a curl): the biceps is the agonist and contracts, while the triceps is the antagonist and relaxes. This decreases the angle at the elbow.
Extending the elbow (straightening the arm): the roles reverse. The triceps is now the agonist and contracts, while the biceps is the antagonist and relaxes, increasing the angle at the elbow.
Markers reward the agonist and antagonist roles, the pull-not-push point, and the correct muscle acting as agonist in each phase.
CCEA A2 20224 marksCompare slow twitch and fast twitch muscle fibres and state a sport suited to each.Show worked answer →
Contrast the two fibre types on their key properties, then match each to a sport.
Slow twitch (type I) fibres contract slowly, generate less force, and are highly resistant to fatigue. They have a rich blood supply and many mitochondria for aerobic energy, so they suit endurance events such as marathon running.
Fast twitch (type II) fibres contract quickly and generate large forces but fatigue rapidly. They rely more on anaerobic energy, so they suit short, explosive events such as sprinting and weightlifting.
Markers reward the contrast in speed, force and fatigue resistance and a correct sport matched to each fibre type.
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