How Johannes Klæbo Trains (Cross-Country Skiing's Bottomless Engine)
At the 2026 Winter Olympics, Johannes Høsflot Klæbo won gold in all six men's cross-country skiing events, the most golds anyone has won at a single Winter Games. A year earlier he'd swept all six events at the World Championships too. He is the most dominant skier the sport has seen, and he happens to compete in the sport that asks more of the aerobic system than almost any other. That combination makes him a perfect lens for the least glamorous, most important idea in endurance training: build an enormous engine, mostly slowly.
The most aerobic sport there is
Cross-country skiing is, by most measures, the hardest test of aerobic capacity in sport. It uses the whole body, arms and legs driving together, so it can demand more oxygen than running or cycling, and elite skiers record some of the highest maximal oxygen uptakes ever measured in athletes. A world-class distance skier is, physiologically, close to the ceiling of what a human aerobic system can do.
You don't build that on intensity. You build it on volume, the overwhelming majority of it easy. This is the same conclusion every sport in this series keeps reaching, from Kipchoge's marathon base to elite rowers' 80-plus percent easy weeks, but cross-country skiing may be where it's pushed furthest, because the aerobic demand of the event is so total that there's no substitute for time spent building the engine.
The I1 to I5 zones, and where the work goes
Norwegian cross-country skiing, the system Klæbo comes out of, organises training into five intensity zones, I1 through I5, from easy aerobic up to maximal. The defining feature of an elite ski program is how much of the year is spent in I1 and I2, the low, conversational end, with only a small, carefully placed dose of the hard I3 to I5 work that gets the headlines.
You can set the same zones for yourself from your maximum heart rate:
Max heart rate
190bpm
| Zone | Range | What it trains |
|---|---|---|
| I1 | I1, Easy 114–137 bpm | Aerobic base (<2 mmol/L lactate). The huge majority of Nordic volume. RPE 2–3, easy, nasal breathing. |
| I2 | I2, Steady 137–156 bpm | Upper aerobic endurance (~2 mmol/L). RPE 4–5, steady. |
| I3 | I3, Threshold 156–165 bpm | Lactate threshold (2.5–4 mmol/L). RPE 6–7, comfortably hard. |
| I4 | I4, VO₂max 165–175 bpm | Maximal aerobic power (4–6 mmol/L). RPE 8–9, hard intervals. |
| I5 | I5, Anaerobic 175–190 bpm | Anaerobic / speed (>6 mmol/L). RPE 9–10, maximal. |
I1 · I1, Easy. Aerobic base (<2 mmol/L lactate). The huge majority of Nordic volume. RPE 2–3, easy, nasal breathing.
I2 · I2, Steady. Upper aerobic endurance (~2 mmol/L). RPE 4–5, steady.
I3 · I3, Threshold. Lactate threshold (2.5–4 mmol/L). RPE 6–7, comfortably hard.
I4 · I4, VO₂max. Maximal aerobic power (4–6 mmol/L). RPE 8–9, hard intervals.
I5 · I5, Anaerobic. Anaerobic / speed (>6 mmol/L). RPE 9–10, maximal.
- The Norwegian/FIS I1–I5 model is the standard across cross-country skiing, biathlon and nordic combined. It pairs heart-rate bands with lactate guideposts (I1 <2 mmol/L up to I5 >6 mmol/L).
- Nordic programs are strongly polarized: enormous volumes of easy I1–I2, with concentrated I3–I5 sessions. Biathletes add the challenge of dropping heart rate fast on the shooting range.
A PDF of your personalized results, with a QR code to reopen them anytime.
It gives you the I1 to I5 bands in beats per minute, so your easy skis stay genuinely easy and your hard sessions are actually hard, instead of everything blurring into a moderate middle. If you cross-train on snow, or roller-ski in summer as the pros do, this is how you keep the bulk of it in the aerobic zones where the engine is built. For the underlying logic, our heart-rate zones guide covers why that distribution works.
What we can and can't say about his training
It's worth being honest here. The fine detail of Klæbo's week, the exact hours, the session-by-session plan, isn't publicly documented in the way it is for some track athletes, so this isn't the place to invent a training diary. What we can say is that his results sit on top of the sport's standard model taken to its highest level: a very large annual training volume, the great majority of it low-intensity, split between snow and summer roller-skiing, with strength and technique work supporting the whole. His edge is partly a freakish engine and partly the ability to combine world-class sprinting with world-class distance skiing, which is its own argument for training the full range of intensities rather than specialising narrowly.
2025 and 2026
Klæbo's dominance in this period is hard to overstate. He swept all six events at the 2025 World Championships, became the first male skier to reach 100 World Cup victories, won multiple overall World Cup titles, and then won all six men's events at the 2026 Olympics. Whatever the details of the plan behind it, the shape is the familiar one: a colossal aerobic base, built patiently, expressed across every distance the sport offers.
What you can actually steal from it
- Build the engine with volume, mostly easy. The most aerobically demanding sport in the world is built on low-intensity work. Yours is too.
- Set real zones. Use the I1 to I5 bands from your max heart rate so easy stays easy and hard stays hard.
- Use snow as free aerobic volume. Skiing and roller-skiing load the engine with less impact than running, exactly the logic behind Kilian Jornet's winter on skis.
- Train the whole range. Klæbo is world-class at both sprint and distance. Don't neglect either the top end or the base.
Klæbo is the most decorated skier alive in the most aerobic sport there is, and the recipe underneath the medals is the same boring, reliable one this whole series keeps landing on: a huge engine, built mostly slowly, over years.
More in this series: Kilian Jornet, elite rowers, Jonas Vingegaard and Eliud Kipchoge.
Sources
Klæbo's titles, including his six-event sweeps at the 2025 World Championships and 2026 Winter Olympics, his 100-plus World Cup wins and his overall titles, are recorded on his Wikipedia profile. The description of cross-country skiing's aerobic demands, elite VO2max values, and the Norwegian I1 to I5 intensity model reflects the established physiology of the sport rather than a published account of Klæbo's specific weekly training, which is not detailed in the public record.
Cover photo by Fil.Al, CC BY 2.0, via Wikimedia Commons.
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