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Every physical activity you perform — from a gentle jog to an explosive 100 m sprint — requires your body to produce energy. The method your body uses to generate that energy depends on the intensity and duration of the activity, and crucially, on whether enough oxygen is available. In this lesson you will learn the two fundamental types of exercise — aerobic and anaerobic — as required by the Edexcel GCSE PE specification (1PE0 — Topic 1: Applied Anatomy and Physiology). You must understand the definitions, the conditions under which each type occurs, and be able to link them to real sporting examples.
The words come from Greek roots:
These terms describe how your body produces energy from glucose, not whether you are breathing or not. Even during anaerobic exercise you continue to breathe — the difference is that oxygen cannot be delivered quickly enough to meet the demands of the working muscles.
The aerobic system is used during low-to-moderate intensity exercise that is sustained for a long period. Because the intensity is manageable, the cardiovascular and respiratory systems can deliver enough oxygen to the working muscles.
Glucose+Oxygen→Energy+Carbon Dioxide+Water
Key points:
| Feature | Detail |
|---|---|
| Intensity | Low to moderate |
| Duration | Long — minutes, hours or even longer |
| Oxygen supply | Sufficient to meet demand |
| Glucose breakdown | Complete |
| By-products | CO₂ and water |
| Energy yield | High per glucose molecule |
| Fatigue onset | Slow |
| Activity | Why It Is Aerobic |
|---|---|
| Marathon running | Sustained moderate pace over 26.2 miles |
| Long-distance swimming | Continuous rhythmic effort over many minutes |
| Road cycling | Steady-state effort for extended periods |
| Playing midfield in football | Continuous moderate running across 90 minutes |
| Jogging | Low intensity, easily maintained |
| Cross-country skiing | Prolonged whole-body effort at moderate intensity |
Exam Tip: Look for trigger words such as "long duration," "steady pace," "moderate intensity," or "continuous." If the performer can sustain the activity for more than two to three minutes at a manageable pace, it is predominantly aerobic.
The anaerobic system is used during high-intensity, short-duration exercise when the body cannot deliver oxygen quickly enough to meet the demands of the working muscles.
Glucose→Energy+Lactic Acid
Key points:
| Feature | Detail |
|---|---|
| Intensity | High to maximal |
| Duration | Short — typically a few seconds up to approximately 60 seconds |
| Oxygen supply | Insufficient to meet demand |
| Glucose breakdown | Incomplete |
| By-product | Lactic acid |
| Energy yield | Low per glucose molecule |
| Fatigue onset | Rapid |
| Activity | Why It Is Anaerobic |
|---|---|
| 100 m sprint | Maximum intensity for approximately 10–12 seconds |
| Javelin throw | Single explosive effort lasting a few seconds |
| Weightlifting (single lift) | Maximal muscular effort for a very short time |
| High jump take-off | Explosive, near-instantaneous action |
| Fast break in basketball | Short, intense sprint to the basket |
| Boxing combination | Rapid, high-intensity burst of punches |
Exam Tip: When identifying anaerobic exercise, look for "short duration," "high intensity," "explosive," "sprint," or "maximal effort." If the performer could not sustain the effort for more than about 60 seconds, it is predominantly anaerobic.
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Meaning | With oxygen | Without oxygen |
| Oxygen used? | Yes | No |
| Intensity | Low to moderate | High to maximal |
| Duration | Long (minutes to hours) | Short (seconds to ~60 s) |
| Glucose breakdown | Complete | Incomplete |
| Energy yield per glucose molecule | High | Low |
| By-products | CO₂ and water | Lactic acid |
| Fatigue | Slow onset | Rapid onset |
| Typical example | Marathon running | 100 m sprint |
graph LR
A[Physical Activity] --> B{Is oxygen supply<br>sufficient?}
B -->|Yes| C[Aerobic System]
B -->|No| D[Anaerobic System]
C --> E[Glucose + O₂ → Energy + CO₂ + H₂O]
D --> F[Glucose → Energy + Lactic Acid]
E --> G[Low-to-moderate intensity<br>Long duration]
F --> H[High intensity<br>Short duration]
It is important to understand that most team sports and many individual sports involve a combination of aerobic and anaerobic exercise. For example, a footballer spends most of the match jogging and running at moderate intensity (aerobic), but performs short sprints, tackles and jumps throughout the game (anaerobic). The dominant system at any moment depends on the intensity of the action being performed.
| Sport | Aerobic Component | Anaerobic Component |
|---|---|---|
| Football | Continuous running for 90 minutes | Sprints, tackles, shots |
| Tennis | Movement around the court between rallies | Explosive serves, lunges, smashes |
| Hockey | Sustained running over 70 minutes | Short sprints, drag flicks |
| Netball | Maintaining position and movement | Quick dodges, jumps for interceptions |
Exam Tip: If an exam question asks you to "Explain which energy system is predominantly used" in a sport, state the dominant system and acknowledge the other system is also used at times. This shows depth of understanding.
In reality, aerobic and anaerobic exercise are not two separate "switches." They exist on a continuum — a sliding scale. At very low intensity, energy production is almost entirely aerobic. As intensity increases, the anaerobic contribution grows. At maximal intensity, the anaerobic system dominates. At any given moment, both systems are contributing; the question is which one is providing the majority of the energy.
graph LR
A["Low Intensity<br>(Walking)"] --- B["Moderate Intensity<br>(Jogging)"]
B --- C["High Intensity<br>(Fast Running)"]
C --- D["Maximal Intensity<br>(Sprinting)"]
A -.- E["Almost 100%<br>Aerobic"]
B -.- F["Mostly Aerobic<br>Some Anaerobic"]
C -.- G["Mixed — increasing<br>Anaerobic contribution"]
D -.- H["Predominantly<br>Anaerobic"]
Understanding the energy continuum helps you write better exam answers. Rather than saying a sport is "aerobic" or "anaerobic," you can explain that the balance shifts depending on the action being performed at that moment.
Question (4 marks): A hockey player jogs back into a defensive position and then sprints to make a tackle. Identify the energy system used for each action and explain the difference between them.
Model answer:
When the hockey player jogs back into a defensive position, the intensity is low to moderate and the activity is sustained, so the aerobic energy system is predominantly used (1). Oxygen is available to break down glucose completely, producing CO₂ and water as by-products (1). When the player sprints to make a tackle, the intensity becomes maximal and the action is very short, so the anaerobic energy system is predominantly used (1). Glucose is broken down incompletely without sufficient oxygen, producing lactic acid as a by-product (1).