Endurance

Aerobic and Anaerobic Training

What aerobic and anaerobic really mean, how your energy systems share the work, and how the balance applies to running, rowing and squash.

In short

• Aerobic and anaerobic are not two kinds of exercise but two ways of producing energy, and both run at all times — what changes with intensity is only the mix.
• In a maximal all-out effort the aerobic system already supplies roughly half the energy by about 75 seconds, so most sessions filed under "anaerobic" are at least half aerobic.
• The aerobic system also pays back what the other two spend, which is why explosive, intermittent sports like squash still need a base: it is what makes you fast repeatedly.
• Lactate is a fuel, not a waste product, and it is not what makes you sore two days later.
• The reliable failure mode is the grey middle — easy days run too hard and hard days run too easy, leaving a week that is too tiring to repeat and too soft to adapt to.

On this page

1. 1.What does aerobic mean?
2. 2.What does anaerobic mean?
3. 3.The role of energy systems
4. 4.Why energy systems are not completely separate
5. 5.Examples of predominantly aerobic activity
6. 6.Examples of predominantly anaerobic activity
7. 7.Application in running
8. 8.Application in rowing
9. 9.Application in squash
10. 10.Combining aerobic and anaerobic training
11. 11.Common misunderstandings

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What does aerobic mean?

Most people arrive at this distinction with a practical question rather than a theoretical one: my sport is short and explosive — why does my plan keep giving me easy aerobic work? The short answer is that the system which carries the easy work is also the system that pays for the hard work, and that is what the rest of this guide is about. The definitions come first because the decision does not make sense without them.

Aerobic means with oxygen. Aerobic training is work your body can supply with energy by burning fuel — mostly fat and carbohydrate — using the oxygen you breathe in.

The defining feature is not speed, and it is not a heart-rate number. It is sustainability. If oxygen delivery can keep up with demand, the effort can continue for a long time: an easy run, a steady row, a brisk walk uphill, a long ride. You could hold a conversation, and you could still be doing it in forty minutes.

Aerobic energy production is slow to start and effectively unlimited in capacity. It is also what most of daily life and most of any endurance sport runs on, which is why an aerobic base is the part of fitness that carries the most transfer.

What does anaerobic mean?

Anaerobic means without oxygen — energy produced faster than oxygen delivery can support it.

This is what covers you when demand spikes: the first seconds of a sprint, a heavy set, a jump, an acceleration to reach a drop shot. It is enormously fast and very limited. Anaerobic energy production cannot be sustained, because the fuel stores it draws on are small and the by-products accumulate.

That accumulation is the burning feeling in a 400 m run or the last reps of a hard set. Worth saying plainly: the lactate produced along the way is not a waste product poisoning your muscles, and it is not what makes you sore two days later. Lactate is itself a fuel, and much of it is used by the heart, the liver and other muscle fibres. The fatigue in a maximal 60-second effort has several causes, and blaming lactate alone is a story that has outlived the evidence for it.

The role of energy systems

There are three, and they differ mainly in how fast they deliver and how long they last.

1. 1Phosphagen (ATP–PCr)About 0–10 seconds

   Instant, maximal, gone quickly · A single heavy lift, a jump, a five-second sprint

2. 2Anaerobic glycolysisAbout 10 seconds–2 minutes

   Very hard, burning, rapidly unsustainable · A 400 m run, a long hard rally, a maximal interval

3. 3Aerobic (oxidative)Minutes to hours

   Steady, repeatable, conversational at the lower end · Everything long: easy runs, steady rows, the recovery between hard efforts

The third system also does a job the first two cannot: it pays back what they spent. Recovery between hard efforts — and between hard sessions — is aerobic work. This is why athletes in explosive, intermittent sports still need an aerobic base. It is not there to make them fast. It is there to let them be fast repeatedly.

Why energy systems are not completely separate

The most common misreading of the picture above is that one system switches off when the next switches on. They never do. All three contribute to almost everything; only the proportions move.

A useful anchor: in a maximal all-out effort, the aerobic system supplies roughly half the energy by about the 75-second mark. Not the ninth minute — the second minute. Efforts most people would file under "anaerobic" — a 600 m run, a two-minute erg test — are already at least half aerobic.

It runs the other way too. Even an easy jog involves a brief anaerobic contribution in its first seconds, before oxygen delivery catches up with demand. Every hill on that jog nudges the mix again.

This is why labelling a session "an aerobic workout" or "an anaerobic workout" is a simplification rather than a description. What a session actually does is emphasise a part of the mix.

Examples of predominantly aerobic activity

• A 45-minute easy run at conversational pace.
• A 60-minute steady row at a pace you could hold for twice as long.
• A long hike, a commute by bike, a swim at a comfortable rhythm.
• The recovery jog between hard intervals — aerobic work doing a specific job.
• Circuit-style training at a moderate effort with short rests, once the first minute has passed.

The common thread is duration and repeatability, not the equipment. A row, a run and a hike at the same effort are training the same quality by different means.

Examples of predominantly anaerobic activity

• A maximal 10-second sprint, a standing jump, a single heavy squat.
• A 400 m run, a 500 m erg piece, a 45-second maximal effort of any kind.
• A set of 8–12 repetitions taken close to failure.
• A hard rally that ends with both players bent over the racket.
• The final sprint of an otherwise aerobic race.

Note that almost every example above sits inside a session that is aerobic overall. That is the normal arrangement, not an exception. How to build a session that deliberately targets one end or the other — the work-to-rest ratios, the interval lengths — belongs to the guide on interval training; this one is about how much of each your week should contain.

Application in running

Running makes the balance easy to see, because pace maps onto it so directly.

For distances from 5 km upwards, the aerobic system is the overwhelming majority of the work, and the fastest route to improvement for most runners is more easy aerobic volume — not more hard sessions. The common failure mode is running easy days slightly too hard, which produces a week of moderate running that is too tiring to repeat often and not hard enough to drive the top-end adaptations.

3 min hard3 min easy jog× 5

The anaerobic side still earns its place: short hill sprints and strides improve running mechanics and recruit fibres that easy running never touches, and they cost very little recovery when kept genuinely short. For a deeper breakdown of how the intensities divide, the guide to training zones 1–5 lays out the full scale.

Application in rowing

A 2000 m race is the textbook mixed effort — roughly six to eight minutes of work in which something like three-quarters of the energy is aerobic, and the remaining quarter, delivered anaerobically at the start and the finish, decides a great many races.

That has a clear training consequence. The bulk of rowing training is long, steady, low-rate aerobic work, because that is what the majority of the race is made of. The sharp anaerobic sessions — 500 m repeats, 250 m starts, race-pace pieces — are a small, precisely placed minority. Reversing the ratio is the classic mistake: it feels like harder training and produces a rower who is fast for ninety seconds.

Application in squash

Squash is the clearest case of why the two systems cannot be trained separately. A rally is a series of maximal accelerations, lunges and changes of direction — anaerobic in nature, lasting seconds. The gap between rallies is short. The match is an hour.

~12s rally~15s between pointsrepeated for an hour

So a squash player trains anaerobic power for the rally and an aerobic base for everything between rallies, and the second one is what tends to be neglected. Court sprints and ghosting build the first. Steady aerobic work off court builds the second, and it is what stops the third game from being a different match than the first.

Combining aerobic and anaerobic training

Three principles do most of the work.

Build the base first. Aerobic fitness underpins the recovery that hard work depends on. A large base makes hard sessions more productive and easier to repeat.

Keep hard work hard and easy work easy. The well-documented failure mode across endurance sports is the grey middle: sessions too hard to be recovery and too easy to be a stimulus. Endurance athletes who improve most tend to spend the large majority of their sessions genuinely easy, and a small minority genuinely hard.

Respect the recovery cost. High-intensity anaerobic work is expensive and takes longer to recover from than its duration suggests. One to two such sessions a week is enough for most people, with easy days in between that stay easy.

Mon

Easy aerobic

40 min, conversational

Tue

Intervals

Hard, anaerobic emphasis

Wed

Rest or mobility

Thu

Easy aerobic

40 min, same as Monday

Fri

Strength

Heavy, low reps, long rests

Sat

Long steady

75–90 min, all aerobic

Sun

Rest

Common misunderstandings

• "Aerobic means low intensity." Aerobic means oxygen-supplied. A marathon run at race pace is extremely demanding and almost entirely aerobic.
• "Anaerobic training is more effective because it is harder." Harder is not the same as more productive. Effectiveness depends on what the goal needs, and for most endurance goals the majority of the benefit comes from the easy work.
• "Lactate causes muscle soreness." It does not. Lactate clears within an hour or so; delayed soreness peaks a day or two later and comes from mechanical stress and the repair that follows.
• "There is a fat-burning zone you must stay in to lose fat." Lower intensities do use a higher proportion of fat, but higher intensities burn more total energy. Fat loss follows overall energy balance, not the fuel mix of one session.
• "Strength training is purely anaerobic." A single heavy set is. A full session, with its rests and its accessory work, has a substantial aerobic component — and your aerobic fitness is part of what determines how quickly you are ready for the next set.
• "You have to choose one." Almost nobody does. The question is the ratio, and for most recreational athletes the ratio should lean heavily aerobic with a small, deliberate amount of hard work on top.

Inside GetMyCoach, this balance is not left to you to assemble. Your plan places the easy aerobic work, the hard intervals and the strength sessions in an order that lets each one do its job — with the intensity of every session stated where you train, so an easy day stays easy.

Sources

1. Gastin, P. — Energy system interaction and relative contribution during maximal exerciseSports Medicine — the source of the roughly 50/50 aerobic-anaerobic split at about 75 seconds.
2. Seiler, S. — What is best practice for training intensity distribution in endurance athletes?International Journal of Sports Physiology and Performance — on keeping easy work easy and hard work hard.
3. Stöggl & Sperlich — The training intensity distribution among well-trained and elite endurance athletesFrontiers in Physiology.
4. ACSM — Guidelines for Exercise Testing and Prescription

Related guides

Keep learning with these related guides.

EnduranceTraining Zones 1–5 ExplainedLearn what each training zone means, how intensity is measured with heart rate, pace, power and perceived effort, and when Zone 1 recovery, Zone 2 aerobic base and hard Zone 4–5 work each belong in a plan.EnduranceInterval Training ExplainedUnderstand how interval training works — work intervals and recovery intervals, short versus long and aerobic versus anaerobic efforts — with practical examples for running, rowing and squash.Training FundamentalsHow Training Plans WorkUnderstand how individual training sessions, training weeks, multi-week blocks and long-term training phases fit together — microcycles, mesocycles, macrocycles and how a structured 12-week plan is built.