AEROBIC BASE: THE FOUNDATION OF EVERYTHING
AEROBIC BASE · ZONE 2
Endurance is the ability to sustain an effort for a long time. Marathon, trail running, cycling, triathlon, ski touring, mountaineering: what defines it is not distance. It's duration.
Aerobic base training is the intensity that lets you last: a slow, comfortable pace where energy comes almost entirely from the aerobic system, the one that uses oxygen to turn fat and carbohydrates into energy.
How do you recognise it?
- You can speak in full sentences without gasping for breath.
- Your heart rate stays around 60 to 75% of your max HR.
- You stay below your first ventilatory threshold (VT1), also called the aerobic threshold.
- In a 5-zone model, it's zone 2.
Most endurance athletes spend 70 to 80% of their training volume there.
WHY IT'S THE FOUNDATION OF TRAINING
Go slow to go further. It sounds counter-intuitive, yet this is where the engine gets built.
Hundreds of hours below the aerobic threshold transform the muscle:
- more mitochondria, the power plants that produce energy;
- more capillaries, to bring oxygen where it's needed;
- better fat utilisation, which spares glycogen for the hard moments.
The result: a faster pace for the same effort, better recovery between hard sessions, and the ability to pile on volume without wearing yourself down.
Consistency matters more than anything. The aerobic system fades fast: one weekend ride or run isn't enough. You need several sessions a week, week after week.
The trap is going too fast. An easy run that's "a bit brisk" falls into the grey zone: too hard to build the base, not hard enough to improve at intensity.
… AND OF METABOLIC HEALTH
Metabolic health is the body's ability to choose its fuel according to the effort: fat when intensity is low, carbohydrates when it rises. This is called metabolic flexibility.
A body that can't use its fat depends on sugar all the time: cravings, energy crashes, needing to eat every 30 minutes during exercise.
Aerobic base training trains exactly this ability. Our glycogen stores hold about 2,000 kcal. Our fat stores, tens of thousands. Knowing how to tap into them changes everything, in training as in daily life.
THE SIZE OF THE ENGINE
The aerobic threshold (AeT, close to VT1) is the point where fat and carbohydrates each supply 50% of the energy. Below it, the effort is sustainable and fuelled mainly by fat. Above it, carbs take over and fatigue builds up.
Two athletes, two engines:
- Too much HIIT. An athlete trained mostly at high intensity switches to carbs from 56% of max HR. An easy jog already costs them sugar.
- Aerobic base. An elite Norwegian cross-country skier stays mostly on fat up to 88% of max HR. He can hold almost his entire effort range for hours.
What makes the difference isn't talent, it's training. Hundreds of hours of aerobic base work shift the threshold to the right. Too much intensity pulls it back to the left.
A more efficient engine. More endurance. More freedom.
The aerobic threshold (AeT, close to VT1) is the point where fat and carbs each supply 50 % of the energy. Data: Training for the Uphill Athlete (S. House, S. Johnston, K. Jornet).
THE OTHER COMPONENTS OF TRAINING
The aerobic base is the foundation. Everything else is built on top of it.
- STRENGTH. An engine needs a chassis that can go the distance. Strength helps you resist fatigue as the hours add up.
- SPECIFIC TRAINING. Running, cycling, climbing, skiing: each discipline has its own demands, and specific work prepares the body for them.
- RECOVERY. You don't improve by training. You improve by recovering.
- NUTRITION. Every session has its own needs. In aerobic base training, the body runs mostly on fat: no point drowning it in sugar. BSE Zone 2 (roasted macadamia, MCT oil, sea salt) is designed for these sessions: 1 pouch every 2 hours.
AEROBIC BASE · STRENGTH · SPECIFIC · RECOVERY · NUTRITION
Frequently asked questions
Generally between 60 and 75% of max HR. The "220 minus age" formula is imprecise: a stress test, or failing that the talk test, gives a more reliable benchmark.
During exercise, speak out loud:
- You speak in full sentences, catching your breath every four or five sentences: you're in Zone 2, the right intensity.
- You can only get a few words out: you're too high. Slow down.
The talk test is a good benchmark, but it remains approximate: heat, altitude, fatigue or stress can skew it. For a more precise measure, do the heart rate drift test, explained in our article on the Zone 2 long run.
An easy run means an easy outing, but many people run it too fast. Aerobic base training is defined by intensity: below VT1, while still able to talk.
Zone 2. Zone 3 is the "grey zone": more tiring without building any more base.
For a short, slow session in a healthy person, it's possible. Beyond 1h30 to 2h, it's better to fuel with something that doesn't shut down fat burning.
