Lesson 4 · Types of training and training methods
Aerobic training: continuous, fartlek, interval and circuit
Almost every endurance athlete in the world does most of their training slowly. Not because slow is easier to schedule, but because the adaptations that make an athlete fast at the end of a race are produced by a volume of work that can only be accumulated at a pace that feels comfortable. This lesson is about how the four aerobic methods divide that work up, and why the division matters.
A club runner has 5 hours a week to train and wants to improve their 10 km time. They decide that since races hurt, every session should hurt, so they run all five sessions as hard as they can.
Predict what happens over eight weeks, and write down two reasons why. Then write what you would change.
- Explain what the aerobic system supplies and why it is trained by volume as much as by intensity.
- Describe continuous, fartlek, aerobic interval and circuit training, and state the distinguishing feature of each.
- Use the aerobic training threshold and the anaerobic threshold to explain where each method sits.
- Assess the relevance of each method for a named sport and a named participant group.
- Explain why a program that is hard every day produces less improvement than one that varies intensity.
- Aerobic — energy supplied with oxygen, at a lower rate than the anaerobic pathways but sustainable for a long time.
- Maximal oxygen uptake — the greatest rate at which an athlete can take in and use oxygen, often the ceiling on endurance performance.
- Aerobic training threshold — the lower intensity boundary, roughly 70 per cent of maximum heart rate, above which an aerobic training effect occurs.
- Anaerobic threshold — the intensity, often around 85 to 90 per cent of maximum heart rate in trained athletes, beyond which lactate accumulates faster than it can be cleared.
- Aerobic training zone — the band of intensities between those two thresholds.
- Continuous training — steady submaximal effort with no rest interval, for a sustained period.
- Fartlek — Swedish for “speed play”, continuous work with unstructured changes of pace.
- Aerobic interval training — repeated bouts within the aerobic zone with defined recoveries.
- Circuit training — a sequence of stations completed in order, with the load, time and rest set by the circuit design.
Aerobic training is bounded above and below. Below the aerobic training threshold the stimulus is too small to force adaptation; the athlete is moving but not training. Above the anaerobic threshold, lactate and hydrogen ions accumulate faster than they can be cleared, and the effort becomes unsustainable, so it is no longer principally an aerobic session.
The band between them is the aerobic training zone, and it is wide. That width is the reason four different methods can all be aerobic and still feel completely different.
| Intensity band | Approximate heart rate | What is happening |
|---|---|---|
| Below the aerobic training threshold | Under about 70 per cent of maximum | Activity with little adaptive stimulus, useful for recovery and for very deconditioned beginners |
| Lower aerobic zone | About 70 to 80 per cent of maximum | Sustainable for a long time, which is what allows large training volume to be accumulated |
| Upper aerobic zone | About 80 to 90 per cent of maximum | Close to the anaerobic threshold, strong stimulus to raise the threshold itself, high fatigue cost |
| Above the anaerobic threshold | Above about 90 per cent of maximum | Lactate accumulates faster than clearance, effort is time-limited, and the session becomes the anaerobic work of Lesson 3 |
A note on the numbers. Percentages of maximum heart rate are a rule of thumb for prescribing training, not a physiological constant. The thresholds move as the athlete adapts, which is itself one of the main goals of aerobic training, and they differ between individuals. Lesson 6 returns to thresholds as a principle of training.
Raising the anaerobic threshold is often more valuable to an endurance athlete than raising maximal oxygen uptake, because it lets the athlete work at a higher percentage of a ceiling they already have.
Quick check: The aerobic training threshold is best described as the intensity:
Each method is a different way of arranging the same total work. The distinguishing feature is worth memorising as a single phrase, because that phrase is usually the mark.
| Method | Distinguishing feature | Typical prescription | Chief strength | Chief weakness |
|---|---|---|---|---|
| Continuous | No rest interval and no planned change of pace | 20 to 90 minutes at 70 to 80 per cent of maximum heart rate | Accumulates large volume at low risk; the foundation of endurance | Monotonous, and poorly matched to sports whose intensity varies |
| Fartlek | Continuous, but pace varies, often chosen by the athlete or by the terrain | 30 to 60 minutes with surges of 30 s to 3 min at irregular intervals | Trains the transition between intensities; enjoyable; suits variable-pace sports | Hard to standardise, so the training load is difficult to record or repeat |
| Aerobic interval | Defined work bouts and defined recoveries, both inside the aerobic zone | 4 to 6 × 4 to 8 minutes near the anaerobic threshold, 2 to 3 min recovery | Accumulates time at a high intensity that could not be held continuously | High fatigue cost, so it is limited to one or two sessions a week |
| Circuit | A sequence of stations, so the exercise changes rather than the pace | 8 to 12 stations, 30 to 60 s each, 15 to 30 s transition, 2 to 4 laps | Trains aerobic fitness alongside strength endurance; needs little space or equipment; scales easily for a group | Intensity is hard to control across a group, and it is less specific to any one sport |
Circuit training deserves a note. It is aerobic when the stations are short, the rest is minimal and the loads are light enough that heart rate stays elevated across the whole circuit. Load the same circuit heavily and rest fully between stations and it becomes resistance training. The design, not the name, decides which it is.
Continuous holds pace constant. Fartlek varies pace without structure. Aerobic interval varies pace with structure. Circuit varies the exercise rather than the pace. Those four clauses distinguish all four methods.
True or false: A circuit is aerobic training only if the loads, station duration and transition times keep the heart rate elevated throughout; the same circuit loaded heavily with full rest is resistance training.
This is the answer to card 01, and it is a genuine insight rather than a piece of folklore.
Many of the adaptations that make an athlete better at endurance are driven by the total accumulated duration of aerobic work: more capillaries supplying the trained muscle, more and larger mitochondria, more enzymes for aerobic energy release, a larger plasma volume and a bigger stroke volume. These are volume-driven. To accumulate the volume, most of it must be done at an intensity the athlete can repeat tomorrow.
A smaller portion of training needs to sit near the anaerobic threshold, because raising that threshold requires working close to it. But that work carries a high fatigue cost, and doing it every day has three predictable effects: total volume falls because the athlete cannot recover, the quality of the hard sessions falls because they are performed tired, and the risk of injury and illness rises.
The failure mode in card 01
Five hard sessions a week produces less improvement than three easy and two hard, despite feeling like more work. Volume collapses, the hard sessions are no longer hard in any useful sense because they are performed in a fatigued state, and the athlete accumulates fatigue faster than adaptation. This is the single most common self-coaching error in endurance sport.
Easy training is not the absence of hard training. It is the thing that makes hard training possible, because it is where the volume comes from and it is what allows the athlete to recover enough to do the hard sessions properly.
Fill the gaps. The band of intensities in which aerobic training is effective lies between the aerobic training threshold and the threshold. Continuous training has no rest interval and no planned change of pace, whereas training is continuous but varies the pace without a fixed structure.
Use the same three-step routine as Lesson 3. Describe the demand profile, match the method to it, and name the trade-off.
| Sport and demand | Best-matched method | Why | Trade-off |
|---|---|---|---|
| Marathon runner: one long effort at a near-constant pace | Continuous, with aerobic interval added | The event is continuous, so most training should be; interval work raises the threshold at which that pace can be held | Continuous work alone leaves the athlete unpractised at surging and finishing |
| Soccer midfielder: continuous movement with unpredictable surges | Fartlek, plus aerobic interval | Fartlek reproduces the unpredictable changes of pace that define the position | Fartlek is hard to quantify, so the training load is difficult to monitor across a squad |
| Rower over 2000 m: sustained work just above the threshold | Aerobic interval near the anaerobic threshold | Accumulates time at an intensity close to race pace that cannot be sustained continuously | Very high fatigue cost; limited to one or two sessions a week |
| Recreational participant returning to activity | Continuous at the lower end, or a light circuit | Safe, sustainable, easy to supervise and easy to progress; a circuit adds variety and strength endurance | Progress can stall if intensity is never raised toward the threshold |
| School squad, forty students, one gym, forty minutes | Circuit | Scales to a large group with minimal equipment and gives every student work at once | Individual intensity is hard to control, so it is a poor choice when precision matters |
Notice the last row. Circuit training is often chosen for a practical constraint, group size and equipment, rather than for a physiological one. Naming that honestly is a stronger answer than pretending the physiological match is perfect.
Two truths and a lie. One of these statements about aerobic training is false. Find it.
Aerobic training is the base of most programs, and it has clear limits that a top-band answer names.
- It does not develop maximal speed or power. Those come from the methods in Lesson 3, and a program built only on aerobic work leaves a team-sport athlete slow over the first ten metres.
- Excessive volume interferes with strength and power gains. High aerobic loads placed alongside heavy resistance training can blunt the strength adaptation, which is why the two are usually separated within a week rather than stacked in one session.
- Adaptation slows as training age rises. A beginner improves on almost any aerobic stimulus; a trained athlete needs an increasingly precise one, which is why threshold work becomes more important over a career.
- It is not the same as being good at the sport. A high aerobic score is a capacity, not a performance. Skill, tactics and decision-making are trained separately, which is Lesson 5.
Activities · design and defend
For each situation, name the aerobic method you would choose, justify it against the demand profile, and state one thing your choice gives up.
A 2000 m rower eight weeks out from a regatta, who can already sustain race pace for 90 seconds but fades badly after that.
A soccer squad whose coach reports they cope with the running but are slow to react to a sudden change of tempo.
A Year 9 physical education class of 40, one indoor court, forty minutes, minimal equipment.
A 52-year-old cleared at screening, inactive for a decade, whose stated goal is to walk a 10 km event in six months.
Match each method to its distinguishing feature.
- Continuous training
- Fartlek training
- Aerobic interval training
- Circuit training
- No rest interval and no planned change of pace
- Continuous work with unstructured changes of pace
- Defined work bouts and defined recoveries, both inside the aerobic zone
- A sequence of stations, so the exercise changes rather than the pace
Return to the runner in card 01: five hours a week, five hard sessions, a 10 km goal, and eight weeks of no improvement.
Rewrite the week. Give five sessions, each with a method, an approximate duration and an approximate intensity as a percentage of maximum heart rate. Then answer two questions in a sentence each: which single change do you expect to produce most of the improvement, and what would you measure in week 8 to know whether you were right?
Lock it in. In one sentence, explain why most of an endurance athlete's training is done below the anaerobic threshold rather than above it.
Assess the relevance of continuous, fartlek, aerobic interval and circuit training for a variety of sports.
Assess requires a judgement against criteria. Four methods are named, so the structure must let you judge each rather than describing all four and then generalising.
Plan: criteria, judge the methods where they are strong, judge where they are weak, then reach a verdict.
These methods will be assessed against how closely they replicate the intensity pattern of the sport, the aerobic adaptation they produce per unit of training time, and their compatibility with the other qualities the athlete must train.
Continuous training — sustained submaximal work — is highly relevant to sports with a steady intensity demand such as distance running, road cycling and triathlon, where it develops the central adaptations of stroke volume and capillary density with low injury risk. Its relevance falls for intermittent sports, because it never replicates the repeated acceleration and recovery those sports require. Fartlek training addresses exactly that gap by varying intensity unpredictably within a continuous session, so it is well matched to football codes and racquet sports where intensity changes are dictated by the contest rather than by a plan.
Aerobic interval training prescribes work and recovery periods deliberately, so it produces a larger stimulus at a controlled intensity and allows progressive manipulation of work-to-rest ratios — which makes it the most precisely adjustable of the four and highly relevant where a specific intensity must be targeted. Circuit training combines aerobic conditioning with resistance and skill stations, so its relevance is greatest where training time is limited or where several qualities must be developed together, though the aerobic adaptation it produces is smaller than an equivalent time spent on dedicated aerobic work.
On balance no single method is most relevant; relevance is determined by the intensity pattern of the sport and the phase of the training year. Continuous work is most relevant when building a base and for steady-state sports, interval work when a specific intensity must be targeted closer to competition, fartlek for intermittent sports, and circuit training where time or the need to train several qualities at once is the binding constraint.
These methods will be assessed against how closely they replicate the intensity pattern of the sport, the aerobic adaptation they produce per unit of training time, and their compatibility with the other qualities the athlete must train. Continuous training develops stroke volume and capillary density with low injury risk and is highly relevant to steady-intensity sports such as distance running, road cycling and triathlon, but its relevance falls for intermittent sports because it never replicates repeated acceleration and recovery. Fartlek training addresses that gap by varying intensity unpredictably within a continuous session, matching football codes and racquet sports where intensity changes are dictated by the contest rather than a plan. Aerobic interval training prescribes work and recovery deliberately, producing a larger stimulus at a controlled intensity and allowing progressive manipulation of work-to-rest ratios, which makes it the most precisely adjustable of the four and most relevant where a specific intensity must be targeted. Circuit training combines aerobic conditioning with resistance and skill stations, so it is most relevant where training time is limited or several qualities must be developed together, although its aerobic adaptation is smaller than an equivalent period of dedicated aerobic work. On balance no single method is most relevant: relevance is set by the sport's intensity pattern and the phase of the training year — continuous work when building a base and for steady-state sports, interval work when targeting a specific intensity nearer competition, fartlek for intermittent sports, and circuit training where time or breadth of quality is the binding constraint.
Explain why an aerobic base is necessary even for athletes competing in predominantly anaerobic sports.
Explain asks for the mechanism. The stem contains an apparent contradiction — aerobic training for an anaerobic sport — and your answer must resolve it.
Plan: name the principle, build linked pairs showing what the aerobic system does during anaerobic work, then answer directly.
The energy systems operate simultaneously rather than in sequence. Anaerobic sports are anaerobic in the efforts they demand, but the recovery between those efforts is aerobic, so aerobic capacity determines how quickly an athlete can repeat a maximal effort.
Resynthesis of creatine phosphate after a maximal effort is an aerobic process, so an athlete with greater aerobic capacity restores that fuel source faster between efforts, which means a smaller decline in power across repeated sprints.
The aerobic system also removes the metabolic by-products accumulated during intense work, so better aerobic conditioning speeds their clearance, which delays the point at which accumulation begins to impair muscle contraction.
Beyond competition, aerobic capacity determines how much high-intensity training an athlete can absorb, since recovery between sessions is also aerobically mediated, which means a stronger base allows a greater volume of the anaerobic work the sport actually requires.
The energy systems operate simultaneously rather than in sequence: anaerobic sports are anaerobic in the efforts they demand, but the recovery between those efforts is aerobic, so aerobic capacity determines how quickly a maximal effort can be repeated. Resynthesis of creatine phosphate after a maximal effort is itself an aerobic process, so an athlete with greater aerobic capacity restores that fuel source faster between efforts and shows a smaller decline in power across repeated sprints. The aerobic system also removes the metabolic by-products accumulated during intense work, so better aerobic conditioning speeds their clearance and delays the point at which accumulation impairs muscle contraction. Beyond competition, aerobic capacity determines how much high-intensity training an athlete can absorb, because recovery between sessions is aerobically mediated, so a stronger base permits a greater volume of the anaerobic work the sport actually requires. An aerobic base is therefore not a compromise for an anaerobic athlete but a precondition for performing and training anaerobically at all — which is why it is built in the off-season, when the specific anaerobic work it supports has not yet begun.
Go back to card 01. Did you predict that the runner would improve at first and then stall, or that they would simply not improve? Did your reasons name the collapse in total volume, the poor quality of hard sessions performed fatigued, or the rise in injury and illness risk? Write down which of the three you had not thought of, and why it matters.
Multiple choice · 5 questions
MC 1. The distinguishing feature of fartlek training is that it is:
- A. performed entirely above the anaerobic threshold
- B. a sequence of stations completed in a set order
- C. continuous work in which the pace varies without a fixed structure
- D. a series of maximal sprints with full recovery
MC 2. An athlete works at an intensity above the anaerobic threshold. The most accurate description is that:
- A. no lactate is produced at this intensity
- B. the aerobic system has stopped contributing energy
- C. the intensity is too low to produce a training effect
- D. lactate accumulates faster than it can be cleared, so the effort is time-limited
MC 3. The main advantage of aerobic interval training over continuous training is that it:
- A. allows an athlete to accumulate time at an intensity they could not sustain continuously
- B. requires less total training time in a week
- C. removes the need for any low-intensity training
- D. develops maximal speed more effectively than sprint training
MC 4. A teacher selects circuit training for a class of 40 students with one court and minimal equipment. The strongest justification is that circuit training:
- A. controls each student's intensity more precisely than any other method
- B. scales to a large group with little equipment while keeping everyone working
- C. is the most sport-specific method available
- D. develops maximal strength faster than resistance training
MC 5. A distance runner trains hard every session for eight weeks and does not improve. The best explanation is that:
- A. hard training cannot improve aerobic capacity
- B. the athlete's anaerobic threshold was already at its physiological maximum
- C. aerobic adaptations require training above the anaerobic threshold only
- D. total training volume fell and the hard sessions were performed in a fatigued state
Short answer · exam style
SA 1. Understand Band 4 Describe continuous training and fartlek training, and explain one sport for which fartlek is the better choice. (4 marks)
SA 2. Analyse Band 5 Using the aerobic training threshold and the anaerobic threshold, explain why an endurance athlete performs most of their training at a moderate intensity. (5 marks)
SA 3. Evaluate Band 6 Assess the relevance of aerobic training methods for a team-sport athlete and for a recreational participant beginning exercise. Justify your choice in each case and identify one limitation. (6 marks)
📖 Comprehensive answers (click to reveal)
Multiple choice: 1 → C. 2 → D. 3 → A. 4 → B. 5 → D.
Activity 1, indicative answers: 1 → Aerobic interval training near the anaerobic threshold, for example 5 × 5 minutes with 2 to 3 minutes of recovery. The rower can already hold race pace briefly, so the limiter is the ability to sustain an intensity close to the threshold, and intervals accumulate time there that could not be held continuously. It gives up training volume and carries a high fatigue cost, so it is limited to one or two sessions a week. 2 → Fartlek. The squad copes with the running volume but not with the transitions, and fartlek trains exactly the change of pace that is failing. It gives up quantifiability, so the coach cannot easily record or repeat the load across a squad. 3 → Circuit training. Forty students, one court and forty minutes is a logistical constraint before it is a physiological one, and a circuit keeps every student working with minimal equipment. It gives up control of individual intensity, so some students will be well inside the zone and others outside it. 4 → Continuous training at the lower end of the zone, progressed gradually, possibly with a light circuit for variety. Safe, sustainable, easy to supervise and directly specific to the walking goal. It gives up threshold development, so progress may stall unless intensity is later raised toward the threshold.
Activity 2, indicative answers: A defensible week: one continuous run of 60 to 75 minutes at 70 to 75 per cent of maximum heart rate; two continuous runs of 35 to 45 minutes at 70 to 75 per cent; one aerobic interval session, for example 5 × 4 minutes at 85 to 90 per cent with 2 minutes of jogging; and one fartlek run of 35 minutes with irregular surges. The single change expected to produce most of the improvement is the reduction from five hard sessions to one or two, which allows total volume to rise and allows the hard sessions to be performed fresh. To test it, repeat a standardised time trial or submaximal test under the same protocol as the baseline, on the same course, at the same time of day.
SA 1 (4 marks): Continuous training is sustained submaximal work with no rest interval and no planned change of pace, typically 20 to 90 minutes within the aerobic zone [1]. Fartlek is also continuous but the pace varies, often unstructured and chosen by the athlete or dictated by terrain [1]. A named sport with variable intensity, such as soccer, hockey, netball or rugby [1], with the justification that the sport's demands are intermittent, so training that changes pace unpredictably reproduces the transitions between intensities that the athlete must actually make in play [1].
SA 2 (5 marks): Define the boundaries: below the aerobic training threshold, roughly 70 per cent of maximum heart rate, the stimulus is too small to force adaptation [1]; above the anaerobic threshold lactate accumulates faster than it is cleared, so the effort is time-limited and the session is no longer principally aerobic [1]. Many key adaptations are volume-driven, including increased capillary density, mitochondrial number and size, aerobic enzyme concentration, plasma volume and stroke volume, and volume can only be accumulated at an intensity that can be repeated the next day [1]. Work near the threshold is necessary to raise the threshold itself, but it carries a high fatigue cost [1]. Therefore most work sits in the lower aerobic zone with a smaller amount near the threshold; training hard every day reduces total volume, degrades the quality of the hard sessions and raises injury and illness risk [1].
SA 3 (6 marks): Three marks per case, awarded for reasoning rather than for the method named. Team-sport athlete: the demand profile is intermittent, with repeated high-intensity efforts and incomplete recovery [1]; fartlek or aerobic interval training matches it, because both reproduce changes of pace and accumulate time at higher intensities [1]; the limitation is that fartlek is difficult to quantify across a squad, and aerobic work alone does not develop the maximal speed and power the sport also requires [1]. Recreational participant: the demand profile is health, safety and adherence rather than performance [1]; continuous training at the lower end of the zone, or a light circuit, is well matched because it is safe, sustainable, easy to supervise and easy to progress [1]; the limitation is that if intensity is never raised toward the threshold, progress stalls, and a circuit gives poor control of individual intensity [1]. A strong response also notes that the same method can serve both groups while doing a different job.
Lessons 3 and 4 are two halves of the same idea: a training method is defined by how work and recovery are arranged, and the arrangement decides which system adapts. Lesson 5 completes the dot point with the methods that are not primarily about energy supply at all.
Before you go on, draw the intensity scale from memory and place all four aerobic methods on it, then add the three anaerobic methods from Lesson 3 above the anaerobic threshold. One diagram now holds the whole of this dot point except skill and flexibility.
Mark lesson as complete
Tick when you've finished the practice and review.