PE2: The Muscular System
Major muscles of the body, antagonistic pairs, roles of muscles and types of muscular contraction.
💪 Major Muscles of the Body
Key Fact: The human body has over 600 skeletal muscles. For GCSE PE, you must know the location and function of the major muscles listed below.
| Muscle | Location | Primary Action | Sporting Example |
|---|---|---|---|
| Biceps | Front of upper arm | Flexes the elbow | Pulling up in a chin-up |
| Triceps | Back of upper arm | Extends the elbow | Pushing phase of a press-up; throwing a javelin |
| Deltoids | Shoulder | Abducts the arm at the shoulder | Bowling in cricket; raising arm in volleyball block |
| Pectorals | Chest | Adducts and flexes the arm at the shoulder | Bench press; butterfly stroke in swimming |
| Latissimus dorsi | Back (lateral/sides) | Adducts and extends the arm at the shoulder | Pulling phase of rowing; pull-up |
| Abdominals | Front of trunk | Flexes the trunk; core stability | Sit-ups; stabilising the core during a plank |
| Gluteals | Buttocks | Extends and abducts the leg at the hip | Driving phase of a sprint; rising from a squat |
| Quadriceps | Front of thigh | Extends the leg at the knee | Kicking a football; upward phase of a squat |
| Hamstrings | Back of thigh | Flexes the leg at the knee; extends the hip | Bending the knee before a long jump; sprinting |
| Gastrocnemius | Back of lower leg (calf) | Plantar flexes the foot | Rising onto toes in a sprint start; jumping |
| Tibialis anterior | Front of lower leg | Dorsiflexes the foot | Lifting toes when walking; keeping feet up in skipping |
⚙️ Antagonistic Pairs
Definition: Muscles work in antagonistic pairs - when one muscle contracts (shortens), the other relaxes (lengthens). This allows bones to move at joints in opposite directions.
Muscles can only PULL; they cannot push. Therefore, to return a bone to its original position, the antagonist must contract while the agonist relaxes.
How Antagonistic Pairs Work - Bicep Curl
Flexion (lifting the weight):
- Biceps contracts (shortens) - this is the agonist
- Triceps relaxes (lengthens) - this is the antagonist
Extension (lowering the weight):
- Triceps contracts (shortens) - now the agonist
- Biceps relaxes (lengthens) - now the antagonist
| Joint | Flexor | Extensor |
|---|---|---|
| Elbow | Biceps | Triceps |
| Knee | Hamstrings | Quadriceps |
| Hip | Iliopsoas (hip flexors) | Gluteals |
| Ankle | Tibialis anterior | Gastrocnemius |
🎭 Roles of Muscles
Agonist (Prime Mover): The muscle that contracts to produce the desired movement. It is the main muscle responsible for the action.
Antagonist: The muscle that relaxes (lengthens) to allow the agonist to work. It may offer some controlled resistance to smooth the movement.
Fixator (Stabiliser): A muscle that contracts isometrically to stabilise the origin of the agonist so it can work effectively. It holds a body part steady while another part moves.
Roles in Action - Bicep Curl
- Agonist: Biceps contracts to flex the elbow and lift the weight
- Antagonist: Triceps relaxes to allow the elbow to flex
- Fixator: Deltoids and rotator cuff contract isometrically to hold the shoulder still, so the biceps can work efficiently on the elbow
Roles in Action - Kicking a Football
- Agonist: Quadriceps contracts to extend the knee and strike the ball
- Antagonist: Hamstrings relaxes to allow the leg to straighten
- Fixator: Gluteals and core muscles stabilise the hip and trunk so the leg can swing powerfully
📐 Types of Muscular Contraction
Isotonic Contraction: The muscle changes length while producing force. Two types exist:
- Concentric: The muscle shortens as it contracts (e.g. upward phase of a bicep curl)
- Eccentric: The muscle lengthens as it contracts under tension (e.g. controlled downward phase of a bicep curl)
Isometric Contraction: The muscle produces force but does not change length. The joint angle stays the same and no visible movement occurs.
| Contraction Type | Muscle Length | Joint Angle | Sporting Example |
|---|---|---|---|
| Concentric (isotonic) | Shortens | Changes | Upward phase of a squat (quadriceps shorten); lifting phase of a bicep curl |
| Eccentric (isotonic) | Lengthens | Changes | Downward phase of a squat (quadriceps lengthen under tension); lowering a weight slowly |
| Isometric | No change | No change | Holding a plank; rugby scrum pushing against equal force; gymnast holding an iron cross |
Identifying Contractions in a Press-Up
- Pushing up (extending arms): Triceps and pectorals contract concentrically (muscles shorten)
- Lowering down (flexing arms): Triceps and pectorals contract eccentrically (muscles lengthen under tension)
- Holding the press-up halfway: Triceps and pectorals contract isometrically (muscles stay same length)
Key Distinctions:
Isotonic = same tension, changing length (movement occurs)
Isometric = same length, no visible movement (holding position)
Concentric = muscle gets shorter
Eccentric = muscle gets longer while under tension (controlling movement)
Isotonic = same tension, changing length (movement occurs)
Isometric = same length, no visible movement (holding position)
Concentric = muscle gets shorter
Eccentric = muscle gets longer while under tension (controlling movement)
🔗 Muscle Fibre Types
| Feature | Type I (Slow Oxidative) | Type IIa (Fast Oxidative Glycolytic) | Type IIx (Fast Glycolytic) |
|---|---|---|---|
| Contraction speed | Slow | Fast | Very fast |
| Force production | Low | Medium | High |
| Fatigue resistance | High (resistant) | Medium | Low (fatigues quickly) |
| Energy system | Aerobic | Aerobic and anaerobic | Anaerobic (lactic acid) |
| Myoglobin content | High (red fibres) | Medium | Low (white fibres) |
| Mitochondria density | High | Medium | Low |
| Capillary density | High | Medium | Low |
| Sporting example | Marathon, long-distance cycling | 800m, team sports, swimming | 100m sprint, weightlifting, shot put |
❓ Practice Questions
Q1: Name the antagonistic pair at the elbow joint and identify the agonist during flexion.
Q2: Explain the difference between concentric and eccentric isotonic contraction, giving a sporting example of each.
Q3: What is the role of a fixator muscle? Give an example from a sporting action.
Q4: During the downward phase of a squat, which type of contraction are the quadriceps performing? Explain why.
Q5: Which muscle is the agonist at the elbow during the pushing phase of a press-up?
Q6: Explain why Type I muscle fibres are more suited to marathon running than Type IIx fibres.
✅ Answers
- The antagonistic pair at the elbow is the biceps and triceps. The agonist during flexion is the biceps (it contracts to flex the elbow while the triceps relaxes).
- Concentric: the muscle shortens while contracting - e.g. the quadriceps shortening during the upward phase of a squat. Eccentric: the muscle lengthens while contracting - e.g. the quadriceps lengthening during the controlled downward phase of a squat.
- A fixator stabilises the origin of the agonist muscle so it can work effectively. During a bicep curl, the deltoids contract isometrically to hold the shoulder still while the biceps works on the elbow.
- Eccentric contraction. The quadriceps are lengthening (the knee is flexing as the body lowers) but the muscle is still under tension to control the speed of descent.
- The triceps is the agonist at the elbow during the pushing phase (it contracts concentrically to extend the elbow).
- Type I fibres are slow-contracting with high fatigue resistance, high myoglobin and mitochondria density, making them ideal for endurance events. Marathon running requires sustained aerobic effort over 26.2 miles. Type IIx fibres fatigue quickly and rely on anaerobic energy, making them unsuitable for prolonged exercise.
🎯 Exam Tips
- Always name the joint, the movement, and the specific muscle in your answers
- Use the words "contracts" and "relaxes" precisely - do not say a muscle "works"
- When asked about antagonistic pairs, name both muscles and state which contracts
- Concentric = shortening, Eccentric = lengthening under tension, Isometric = no change
- The agonist is also called the prime mover
- Isometric contractions are common in gymnastics holds, rugby scrums and yoga
- Muscle fibre types are Higher-tier content - make sure you can compare all three types
⚠️ Common Errors
Watch Out!
Students often say muscles "push" bones. Wrong: "The triceps pushes the arm straight." Correct: "The triceps contracts (pulls) to extend the elbow."
Students often confuse agonist and antagonist. Wrong: "The antagonist is the muscle doing the work." Correct: "The agonist (prime mover) is the muscle contracting to produce the movement."
Students think eccentric contraction means the muscle is relaxed. Wrong: "In the downward phase of a squat, the quadriceps relaxes." Correct: "In the downward phase, the quadriceps contracts eccentrically (lengthening under tension) to control the descent."
📝 Exam Technique
PE Exam Tips — The Muscular System:
1. For The Muscular System questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of The Muscular System to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
1. For The Muscular System questions, use subject-specific terminology precisely
2. Support every point with specific evidence or examples
3. Show balanced analysis — consider different perspectives before reaching a conclusion
4. Link your understanding of The Muscular System to real-world contexts where possible
5. For longer answers, plan your response to address all parts of the question
⚠️ Common Errors
Watch Out!
Students often think lactic acid causes doms. Wrong: Lactic acid causes DOMS Correct: DOMS (delayed onset muscle soreness) is caused by micro-tears in muscle fibres, not lactic acid. Lactic acid is cleared within an hour of exercise.
Students often think veins always carry deoxygenated blood. Wrong: Veins always carry deoxygenated blood Correct: Pulmonary veins carry oxygenated blood from the lungs to the heart. It is arteries and veins relative to the heart that matters, not oxygenation.
Students often think the heart beats faster during exercise just because you need more oxygen. Wrong: The heart beats faster during exercise just because you need more oxygen Correct: Heart rate increases due to anticipatory rise (before exercise), increased CO2 in blood detected by chemoreceptors, and decreased vagal tone. It is a coordinated response, not just oxygen demand.
✍️ Model Answer
Full-Mark Response
6 marks: Explain how the muscular system affects sporting performance.
The Muscular System has significant effects on sporting performance. [Key concept 1]: explain the mechanism with specific detail. [Key concept 2]: how this applies in a named sporting example. [Key concept 3]: the relationship between this topic and overall performance. A grade 9 answer uses precise anatomical/physiological terminology, specific sporting examples, and evaluates the relative importance of different factors.
Mark scheme: 2 marks per explained point with specific evidence, evaluation for top marks
📊 AO Deep Dive
Assessment Objective Analysis
GCSE PE tests four AOs: AO1 (Knowledge, 30%) — recall facts about The Muscular System including definitions, classifications and specific examples; AO2 (Application, 30%) — apply knowledge to sporting contexts and training scenarios; AO3 (Analysis and Evaluation, 25%) — analyse data (graphs, tables), evaluate training methods or strategies, and justify recommendations; AO4 (Practical, 15%) — demonstrate relevant skills. For grade 9, use precise terminology, support every point with named sporting examples, and evaluate rather than just describe. The difference between grade 5 and grade 9 is the quality of application and depth of evaluation.
📝 Exam Questions by Topic
🎬 Video Resources
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