⚖️ 80/20 in endurance training: Brilliant rule of thumb – or just a numbers game?

Why Stephen Seiler and Sebastian Weber contradict each other less than it seems at first glance – and what ambitious cyclists and trail runners should really take away from it.

Reading time: approx. 8 minutes

Hello! 👋

80 percent easy. 20 percent hard.

Sounds wonderfully simple, doesn't it?

You watch TrainingPeaks on Sunday evening, do a quick calculation and think: "That fits. Ten hours this week, so two hours hard."

This is precisely where Sebastian Weber from INSCYD would likely raise his hand. In his recent video on the 80/20 rule, he argues rather provocatively: The percentage shouldn't be the training goal. It's more a result of how much total training volume you're doing and how many hard minutes you can reasonably tolerate.

Stephen Seiler, in turn, has spent many years describing precisely those training patterns from which the “80/20” method became popular.

So, who is right?

Spoiler alert: Probably both – if you clearly define what you're talking about. 😉

And that's precisely the crux of the matter.

1️⃣ The first mistake: 80/20 is not the same as 80/20

Seiler's early work on elite endurance athletes did not simply describe the rule:

"20 percent of your training time must be above the threshold."

Rather, he observed that successful athletes complete a very large part of their training sessions at a relaxed pace and design a smaller part as intensive key sessions.

In the classic three-zone logic, this means:

• Zone 1: below LT1 / first ventilatory threshold → loose

• Zone 2: between LT1 and LT2 → moderate / pace / near threshold

• Zone 3: above LT2 → high intensity

That sounds trivial, but it's crucial.

Because there are at least three ways to count the same training week:

1. Session Goal: What was the main intention of the session?

2. Time in Zone: How many minutes were actually in each zone?

3. Heart rate, pace or power zones: and even here, different systems can deliver completely different numbers.

A 90-minute bike ride with 5 x 5 minutes of VO₂max can be considered a "hard session" according to the session goal method. However, according to the time-in-zone method, perhaps only 25 minutes are actually above LT2.

The same week can therefore be both "80/20" and "90/10" at the same time.

Welcome to the wonderful world of exercise science. 😄

And this is precisely where Weber begins.

2️⃣ Sebastian Weber: “The percentage is the result”

Weber presents two extremes in his video.

An amateur athlete trains only a few hours per week. Many hours of recovery lie between sessions. From a purely physiological standpoint, this athlete can tolerate a significantly higher percentage of intensive work.

A professional athlete, on the other hand, trains 25 to 30 hours a week. If they were to actually dedicate 20 percent of their total training time to high-intensity training, that would amount to five to six hours of true high intensity per week. Practically unrealistic.

Weber's core idea is therefore:

Look first at the sensible absolute dose of intensive work – and only then at the percentage.

In his example, he often ends up with roughly 90 to 120 minutes of hard net work per week. The larger the overall workload becomes, the smaller the percentage automatically becomes.

That's logical. But you have to be careful here.

Because a clear model quickly becomes the next magic rule:

"Aha. So 90 minutes of HIT is optimal."

No. It's not that simple.

The tolerable dose depends on several factors, including:

• Intensity and interval format

• Training status,

• Sport,

• Carbohydrate availability,

• Season phase,

• Age and recovery,

• additional professional and family burdens.

Weber refers, among other things, to the work of Flockhart et al., in which progressive overload with very high HIIT was ultimately associated with a deterioration of mitochondrial function. Interesting – but: This was a small experimental study with eleven participants and not proof of a universal 90-minute limit .

👉 The better message is therefore: Intensity has a dose-response curve. More is not automatically better.

3️⃣ And what does Seiler say about it today?

Recent research actually makes the story even more interesting.

A large meta-analysis by Oliveira et al. from 2024 compared polarized training with other intensity distributions.

Result: Polarization can bring advantages – but superiority is by no means clear in all situations.

Even more interesting is the Individual Participant Network meta-analysis by Rosenblat et al. (2025):

Polarized and pyramidal designs did not differ significantly overall in VO₂max or time-trial performance.

But the subgroups were interesting:

• Athletes with greater competitive experience might be more likely to react to a more polarized distribution.

• Recreational and less highly developed athletes may be better suited to a pyramidal distribution.

And a recent meta-analysis specifically of trained cyclists also comes to a soberingly simple result:

Polarized and non-polarized improved VO₂max and time trial performance similarly.

This is important.

Because current science does not say:

"80/20 is wrong."

She says more like:

"There is no magic distribution that is superior for all athletes, sports, and training phases."

4️⃣ The “grey zone” is not automatically evil 🚦

One of the biggest collateral damages of the 80/20 debate is the reputation of medium intensities.

Pace. Sweet spot. Threshold. Moderate intervals.

Is it all a "grey area"?

It's not quite that simple.

In 2025, Bent Rønnestad and colleagues demonstrated in highly trained cyclists that both a block of moderate intervals and a block of high-intensity intervals improved 15-minute performance. At the 4 mmol power point, the moderate block was even more effective.

That fits well with the practice of the Norwegians.

The best-practice study published in 2024 by Tønnessen, Sandbakk, Seiler and colleagues shows approximately the following among Norwegian world-class endurance athletes:

• 75–80% of the units are low intensity ,

• 10-15% moderate intensity ,

• 5–10% high intensity .

This is not about "avoiding the middle at all costs".

It is rather:

Take it easy. Use moderate work sparingly. Use very hard work sparingly.

Olav Aleksander Bu puts it similarly from a coach's perspective: Quality is not the same as intensity. A relaxed session can be high-quality – and a threshold session can be bad if it's done too hard and ruins the next key days.

5️⃣ San Millán and the Zone 2 chaos 🔥

Another nerdy detail that causes a lot of confusion:

San Millán's "Zone 2" is not Seiler's Zone 2.

San Millán uses a multi-zone model. Its famous Zone 2 lies roughly in the upper aerobic range below LT1 , or around high fat oxidation and low lactate accumulation.

In the Seiler three-zone model, a large part of this would simply be Zone 1 – Low Intensity .

So if a podcast says:

"Pogačar drives an incredible amount in Zone 2"

and another says:

"Polarized training avoids Zone 2"

Both statements can be true at the same time. 🤯

The 2025 expert report on the definition of "Zone 2" highlights precisely this problem: even among sports scientists and coaches, there is no completely uniform definition.

Therefore, my advice is:

Talk less about zone numbers – and more about physiological ranges.

Below LT1. Between LT1 and LT2. Above LT2.

That's much clearer.

6️⃣ Jack Daniels and Renato Canova probably wouldn't even count 🏃♂️

A look at the world of running is also exciting.

Jack Daniels structures training according to a clear purpose: Easy, Marathon, Threshold, Interval, Repetition. His quality work is strictly measured, with the majority of the running remaining easy. The crucial question, however, is not whether exactly 80.0 percent of the effort is achieved in the end.

His favorite question is, in essence, much more practical:

"What is the purpose of this unit?"

Renato Canova focuses even more strongly on race specificity. In his marathon philosophy, the distribution changes over the course of the season: broader and more general early on, later getting closer and closer to the specific race pace.

This directly contradicts the idea of maintaining the same rigid intensity distribution for twelve months.

And that's exactly the point:

Training is periodization – not an Excel constant.

7️⃣ What does this mean specifically for trail running? ⛰️

Trail running makes percentage calculations even more complicated.

A four-year case study of an elite trail runner, published in 2024, found an average training distribution of 75% low, 18% moderate, and 7% high – clearly pyramidal. Particularly significant improvements in LT1 and LT2 even occurred in a year with approximately 30% moderate training.

This is just one athlete and therefore not proof that "higher threshold is better".

But it shows why models should not be applied dogmatically.

In the trail, the following also counts:

• Heart rate increases uphill at a low pace.

• When going downhill, heart rate can be low while eccentric muscle exertion is high.

• Technical trails increase neuromuscular fatigue,

• Altitude and terrain massively alter the load.

A two-hour trail run can be cardiovascularly "easy" but still brutal for the muscles.

A pure HR zone distribution does not account for this.

8️⃣ What would I recommend to ambitious amateur athletes?

This is where it becomes relevant for aecoaching.

Most of my target athletes don't train 25 hours a week.

But rather 6 to 15 hours per week – in addition to work, family and the rest of life.

🚴 6–7 hours per week

I would n't force 80 percent easy here if it only results in four hours of very light rolling and at the same time insufficient effective training stimulus.

Mostly useful:

• 1-2 genuine quality days,

• 1 longer aerobic session,

• remaining units easily,

• Use moderate work in a targeted manner.

A sweet spot or threshold block is not automatically "junk".

🚴🏃 9–11 hours per week

This is probably the classic ambitious age-grouper.

This often works:

• two key days per week,

• a large proportion under LT1,

• a targeted moderate or threshold stimulus,

• a VO₂max/high-intensity stimulus depending on the phase,

• a longer aerobic session.

If the result is 75/15/10 or 80/12/8: wonderful.

But the number is the result of planning – not the starting point.

🏔️ 12–15 hours per week

Now something interesting is happening:

The proportion of low-intensity training increases almost automatically because you simply can't train hard every extra hour.

The number then often approaches the classic pattern of successful elite programs – not because you “follow” the 80/20 rule, but because high training volumes without plenty of light training do not work in the long run.

9️⃣ A better rule than 80/20 🎯

If I had to choose a rule of thumb, it wouldn't be 80/20.

But these:

Make the easy sessions easy enough so that the important sessions can be truly high quality.

Then come five questions:

What is my competition goal?

What physiological ability do I want to develop right now?

How much total volume can I realistically regenerate?

What additional stress does my sport create?

Can I easily repeat the key sessions week after week?

Once these questions are answered, the intensity distribution usually becomes almost automatic.

🔟 My Coach Conclusion

80/20 is an excellent reminder that endurance sports shouldn't be hard every day.

However, as a rigid mathematical training rule, it is significantly less convincing.

Seiler primarily showed us a robust pattern of successful endurance programs:

Lots of relaxed, little really hard work.

Weber rightly reminds us:

A percentage without a total scope is almost worthless.

Rønnestad and the Norwegian school demonstrate:

Moderate and threshold work also has a clear place.

San Millán reminds us of the metabolic importance of the aerobic foundation.

Daniels and Canova would add:

Every unit needs a purpose – and training must become more specific to the competition.

My conclusion from this?

Don't train with an 80/20 split. Instead, train in such a way that a sensible intensity distribution is achieved in the end.

That sounds less sexy than a fixed formula.

But it's quite likely the better training plan. 😉

🤝 You have 6-15 hours – but you're tired of percentage roulette?

If you're currently wondering whether you have too much of a relaxed, too much of a threshold, or too much of a "kind of middle ground" attitude, we can take a look at exactly that together.

At aecoaching.at, you can now get a free 45-minute initial consultation . We'll talk about your goal, your daily routine, your current training structure – and what distribution actually makes sense for you .

👉 Book a free initial consultation: https://www.aecoaching.at/general-6

No 80/20 template. But training that fits your body, your life, and your goal.

Alex | aecoaching.at 🚴♂️🏃♂️⛰️

📚 Scientific sources

1. Seiler, S. (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance, 5(3), 276–291. DOI: 10.1123/ijspp.5.3.276

2. Seiler, KS, & Kjerland, G. Ø. (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an optimal distribution? Scandinavian Journal of Medicine & Science in Sports, 16(1), 49–56. DOI: 10.1111/j.1600-0838.2004.00418.x

3. Oliveira, PS, et al. (2024). Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes' Endurance Performance: A Systematic Review with Meta-analysis. Sports Medicine, 54, 2071-2095. DOI: 10.1007/s40279-024-02034-z

4. Rosenblat, MA, et al. (2025). Which Training Intensity Distribution Intervention will Produce the Greatest Improvements in Maximal Oxygen Uptake and Time-Trial Performance in Endurance Athletes? Sports Medicine, 55, 655-673. DOI: 10.1007/s40279-024-02149-3

5. Cove, B., et al. (2025). The effect of training distribution, duration, and volume on VO₂max and performance in trained cyclists. Journal of Science and Medicine in Sport, 28(5), 423-434. DOI: 10.1016/j.jsams.2024.12.005

6. Tønnessen, E., Sandbakk, Ø., Sandbakk, SB, Seiler, S., & Haugen, T. (2024). Training Session Models in Endurance Sports: A Norwegian Perspective on Best Practice Recommendations. Sports Medicine, 54, 2935-2953. DOI: 10.1007/s40279-024-02067-4

7. Sandbakk, Ø., et al. (2025). Best-Practice Training Characteristics Within Olympic Endurance Sports as Described by Norwegian World-Class Coaches. Sports Medicine - Open, 11, 45. DOI: 10.1186/s40798-025-00848-3

8. Rønnestad, BR, et al. (2025). Block Training With Moderate- or High-Intensity Intervals Both Improve Endurance Performance in Well-Trained Cyclists. European Journal of Sport Science, 25(11), e70067. DOI: 10.1002/ejsc.70067

9. Mølmen, KS, et al. (2025). A Moderate-Intensity Interval Training Block Improves Endurance Performance in Well-Trained Cyclists. Medicine & Science in Sports & Exercise, 57(8), 1780-1789. DOI: 10.1249/MSS.0000000000003706

10. Muniz-Pumares, D., Hunter, B., Meyler, S., Maunder, E., & Smyth, B. (2025). The Training Intensity Distribution of Marathon Runners Across Performance Levels. Sports Medicine, 55(4), 1023-1035. DOI: 10.1007/s40279-024-02137-7

11. Rivera-Kofler, T., et al. (2024). Anthropometric Characteristics, Training Intensity Distribution, Physiological Profile and Performance of an Elite Trail Runner: A Longitudinal Case Study. International Journal of Morphology, 42(2), 416–423. DOI: 10.4067/S0717-95022024000200416

12. Sitko, S., et al. (2025). What is “Zone 2 Training”?: Experts' Viewpoint on Definition, Training Methods, and Expected Adaptations. International Journal of Sports Physiology and Performance, 20(11), 1614-1617. DOI: 10.1123/ijspp.2024-0303

13. San-Millán, I., & Brooks, GA (2018). Assessment of Metabolic Flexibility by Means of Measuring Blood Lactate, Fat, and Carbohydrate Oxidation Responses to Exercise in Professional Endurance Athletes and Less-Fit Individuals. Sports Medicine, 48(2), 467-479. DOI: 10.1007/s40279-017-0751-x

14. Flockhart, M., et al. (2021). Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy volunteers. Cell Metabolism, 33(5), 957–970.e6. DOI: 10.1016/j.cmet.2021.02.017

🎙️ Practical and coaching resources

Sebastian Weber / INSCYD (2026): The 80/20 Rule Doesn't Work in Endurance Training. Video from November 10, 2026.

Sebastian Weber / INSCYD (2023): Polarized vs pyramidal training: which suits your athlete?

Jack Daniels: Daniels' Running Formula (4th ed., Human Kinetics, 2021) and VDOT methodology.

Renato Canova: Training philosophy for General → Special → Specific and race-specific endurance.

Olav Aleksander Bu: Interviews and practical contributions on individualized intensity control and the “Norwegian Method”.