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This final lesson in the Aerobic and Anaerobic Exercise topic brings everything together. In the AQA GCSE PE exam, you will be expected to apply your knowledge of energy systems to specific sporting scenarios — identifying which system is being used, justifying your answer with reference to intensity and duration, and explaining the physiological effects on the performer. This lesson provides a structured approach to answering these application questions.
The energy system used depends on two factors:
| Factor | Aerobic | Anaerobic |
|---|---|---|
| Intensity | Low to moderate | High to maximal |
| Duration | Long (minutes to hours) | Short (seconds to ~60 seconds) |
These two factors are your primary tools for justifying which energy system is being used. Every exam answer about energy systems should reference at least one of them.
graph TD
A[Identify the Activity] --> B{"What is the<br>INTENSITY?"}
B -->|Low to moderate| C{"What is the<br>DURATION?"}
B -->|High to maximal| D{"What is the<br>DURATION?"}
C -->|Long - minutes to hours| E["Predominantly<br>AEROBIC"]
C -->|Short burst within<br>longer activity| F["Mix of both -<br>see energy continuum"]
D -->|Short - seconds to<br>~60 seconds| G["Predominantly<br>ANAEROBIC"]
D -->|Sustained high intensity<br>for minutes| F
style A fill:#4a90d9,color:#fff
style E fill:#27ae60,color:#fff
style G fill:#e74c3c,color:#fff
style F fill:#f39c12,color:#fff
These are activities performed at low-to-moderate intensity over an extended period.
| Sport/Activity | Typical Duration | Intensity | Why Aerobic? |
|---|---|---|---|
| Marathon | 2–5+ hours | Low to moderate | Sustained effort over a very long duration; oxygen supply meets demand |
| Recreational swimming | 20–60 minutes | Low to moderate | Rhythmic, continuous movement at a manageable pace |
| Road cycling | 1–6+ hours | Low to moderate | Prolonged effort; body can maintain oxygen delivery |
| Hiking / brisk walking | 1+ hours | Low | Very low intensity sustained over a long period |
| Cross-country running | 20–40 minutes | Moderate | Sustained running at a pace below maximum |
Physiological explanation: In aerobic activities, the body uses the aerobic energy equation: glucose + oxygen → energy + CO2 + water. Because oxygen supply meets demand, there is no significant lactic acid build-up, and the activity can be sustained for long periods.
These are activities performed at high-to-maximal intensity for a short duration.
| Sport/Activity | Typical Duration | Intensity | Why Anaerobic? |
|---|---|---|---|
| 100 m sprint | 10–12 seconds | Maximal | Flat-out effort; duration far too short for aerobic system to dominate |
| Shot put | 1–2 seconds (throw) | Maximal/explosive | Single explosive action; maximum force for minimum time |
| Weightlifting (1RM) | A few seconds | Maximal | Maximum load lifted in a single explosive effort |
| Long jump | ~2 seconds (run-up and jump) | Maximal | Short, explosive action requiring maximum power |
| Javelin throw | ~2 seconds (delivery) | Maximal | Explosive release requiring maximum force |
| Gymnastics vault | ~5 seconds | Maximal | Short, explosive run-up and vault |
Physiological explanation: In anaerobic activities, the body uses the anaerobic energy equation: glucose → energy + lactic acid. The intensity is so high that the body cannot deliver oxygen fast enough, so glucose is broken down without oxygen. The activity must be short because lactic acid builds up rapidly, causing fatigue.
Most team sports and many individual sports involve both energy systems. The performer switches between aerobic and anaerobic depending on the demands at any given moment.
| Sport | Aerobic Component | Anaerobic Component |
|---|---|---|
| Football | Jogging between plays, maintaining position (~90 mins) | Sprinting for the ball, jumping for headers, shooting |
| Rugby | Jogging back into position, sustained play | Sprinting, tackling, scrummaging |
| Tennis | Moving around the court between rallies (~1–5 hrs) | Explosive serves, sprint to the net, overhead smash |
| Basketball | Moving around the court, marking opponents | Fast breaks, jump shots, explosive rebounds |
| Cricket | Fielding (walking/jogging for extended periods) | Bowling (explosive action), batting (explosive shots), sprint between wickets |
| Hockey | Sustained movement throughout the match (~70 mins) | Short sprints, drag flicks, tackles |
| Badminton | Rally play, court movement (~30–90 mins) | Explosive smashes, lunges, jump shots |
| Boxing | Moving around the ring, maintaining guard (~12 rounds) | Explosive combinations, power punches |
Exam Tip: When discussing a sport that uses both systems, identify specific actions within the sport and classify each one. For example, in football: "A midfielder jogging back into position is working aerobically because the intensity is low and the duration is sustained. However, when they sprint to win a tackle, they switch to the anaerobic system because the intensity becomes maximal and the action is short-lived."
For any question asking you to apply energy systems to sport, use this framework:
| Step | Action | Example (Tennis Serve) |
|---|---|---|
| I — Identify | Name the energy system | The tennis serve predominantly uses the anaerobic energy system |
| D — Duration | State the duration of the action | The serve takes approximately 1–2 seconds |
| E — Energy equation | State the relevant equation | Glucose → energy + lactic acid |
| A — Analyse effects | Explain the physiological consequences | Due to the maximal effort, lactic acid is produced; however, as the action is very brief, accumulation is minimal. Between serves, the aerobic system is dominant, allowing partial recovery. |
Question: A 1500 m runner competes in a race. Explain which energy system(s) the runner uses and justify your answer.
Model Answer:
The 1500 m runner predominantly uses the aerobic energy system for the majority of the race because the intensity is moderate and the duration is approximately 3.5–4 minutes, allowing the body to supply sufficient oxygen to the working muscles. The aerobic equation is used: glucose + oxygen → energy + CO2 + water. (2 marks)
However, during the sprint finish in the final 200–300 m, the runner switches predominantly to the anaerobic energy system because the intensity increases to near-maximal for a short burst. At this point, oxygen supply cannot meet demand, so glucose is broken down without oxygen: glucose → energy + lactic acid. This causes lactic acid to accumulate, leading to muscle fatigue and the characteristic "burn" in the legs as they cross the finish line. (2 marks)
Question: Compare the energy systems used by a marathon runner and a 100 m sprinter. Explain how the different energy systems affect each performer during and after their event.
Model Answer:
During the event:
A marathon runner predominantly uses the aerobic energy system. The intensity is low to moderate and the duration is 2–5+ hours, meaning the body can supply enough oxygen to meet the energy demands. The equation is: glucose + oxygen → energy + CO2 + water. The by-products (CO2 and water) are harmless and easily removed — CO2 is breathed out and water is lost through sweat. Because no lactic acid builds up, the runner can sustain the effort for a long duration. (3 marks)
A 100 m sprinter predominantly uses the anaerobic energy system. The intensity is maximal and the duration is only 10–12 seconds, meaning the body cannot supply oxygen fast enough. The equation is: glucose → energy + lactic acid. Less energy is produced per molecule of glucose because the breakdown is incomplete. Lactic acid builds up rapidly in the muscles, causing fatigue and a burning sensation. This is why the sprinter cannot maintain their pace for more than about 12 seconds. (3 marks)
After the event:
The marathon runner's recovery is primarily about replenishing glycogen stores and rehydrating — they will feel fatigued and may experience DOMS in the following days, but minimal lactic acid removal is needed because the exercise was predominantly aerobic.
The sprinter must repay an oxygen debt (EPOC) — they will breathe heavily after the race to take in extra oxygen, which is used to break down lactic acid in the liver. Their recovery from lactic acid is quicker (minutes), but the overall recovery process includes both EPOC and glycogen replenishment.
| Scenario | Predominant Energy System | Key Justification |
|---|---|---|
| "A swimmer completes a 50 m freestyle race in 25 seconds." | Anaerobic | High/maximal intensity, short duration (25 s) |
| "A cyclist rides 100 km in a sportive event." | Aerobic | Moderate intensity, very long duration (hours) |
| "A basketball player performs a fast break." | Anaerobic | Explosive sprint, short duration, high intensity |
| "A basketball player throughout a full game." | Both (aerobic dominant with anaerobic bursts) | Game lasts 40+ minutes (aerobic), but includes explosive sprints and jumps (anaerobic) |
| "A gymnast performs a floor routine." | Both (anaerobic dominant) | Explosive movements (anaerobic) within a ~90 second routine |
| "A rower competes in a 2000 m race (~6-7 mins)." | Predominantly aerobic with strong anaerobic component | Sustained effort (aerobic) at high intensity with sprint start and finish (anaerobic) |
When you apply energy systems to sport, you can also link to the effects of exercise:
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