A principle popularized by physiologist Stephen Seiler: 80% of your training should be so easy that you can hold a comfortable conversation, and 20% so hard that talking is out of the question.

We've passed the “vehicle inspection” and know everything about our “engine.” It's finally time to hit the road! The training process is not just mindlessly grinding out kilometers. It's the art of managing intensity, much like working a car's gearbox. For every task there is a “gear” of its own — or, as they say in sport, an “intensity zone.”

The running world uses different systems: 3-zone (simple), 5-zone (classic) and 6-zone (detailed). For the ultramarathon, the 6-zone system (Zone 0–5) is the perfect fit: high-intensity work is divided more precisely — the threshold zone (Zone 4) and VO2max (Zone 5) are separated out, plus there is a dedicated recovery zone (Zone 0). This lets you dose the load more accurately at every intensity level.

4.1. Zone 0 (Recovery): “Neutral” — the Art of Resting Actively

50–60% of maximum heart rate. This isn't even a workout — it's what you do BETWEEN them. An easy walk, stretching, a foam roller, relaxed swimming in the pool. Your heart rate barely rises.

The classic beginner's mistake is to lie on the couch “like a corpse” after a hard session. Light activity helps get the blood moving and moderately speeds up the clearance of metabolic by-products; science doesn't give exact percentages here, but the principle of “better to take a walk than to lie flat” holds up. So active recovery is not laziness — it's a smart move.

4.2. Zone 1 (FatMax): “First Gear” — the Zone Where Ultramarathoners Are Made

60–70% of maximum heart rate. This is your “workhorse,” the main zone for an ultramarathoner. Here the body burns the maximum amount of fat per minute. How does it feel? Very comfortable running — you can speak freely in full sentences.

It is in this boring, slow, almost meditative zone that the real miracles happen:

Mitochondria grow — your “power plants” inside the muscles. The more of them there are and the bigger they get, the more fat you can burn.
The capillary network expands — new “roads” for delivering oxygen grow toward the muscles.
VLamax decreases — the body learns not to squander carbohydrates and “patches the hole in the gas tank.”

Sessions in this zone should be long. Two, three, four hours… This is exactly how we teach the body to run on fat. Yes, it can be mentally tough to run this slowly while pensioners walking their dogs overtake you. But believe me, in the second half of your ultra you'll thank yourself for it.

4.3. Zone 2 (Extensive Endurance): “Second Gear” — Long Steady Efforts

This is the zone just above the aerobic base (70–75% of maximum heart rate). Here you're already running a “steady” effort — comfortable, but noticeably faster than in Zone 1. You can speak in short phrases, but you can no longer chatter away nonstop.

This zone is useful for:

long steady-state sessions (1.5–2 hours);
developing muscular endurance;
preparing for long endurance races.

For an ultramarathoner, Zone 2 is roughly 10–15% of training time. Not the foundation of preparation, but a useful supplement to the base work in Zone 1.

4.4. Zone 3 (Intensive Endurance): “Third Gear” — Marathon Pace

Now it gets more serious. This is the zone of 75–82% of maximum heart rate — roughly your half-marathon or marathon pace. Talking is already difficult; breathing is rapid but under control.

Workouts in this zone:

tempo segments of 20–40 minutes;
long intervals (3–4 times 10 minutes);
marathon pace at the end of long runs.

For an ultramarathoner this is about 5–10% of training time. It helps push the thresholds upward and maintain your “speed fitness.”

4.5. Zone 4 (Anaerobic Threshold, LT2): “Fourth Gear” — on the Edge

This is the zone of your anaerobic threshold (82–89% of max heart rate). Running is hard, talking is impossible, breathing falls apart. Lactate accumulates, and holding this intensity for long is impossible. This is your 10K or fast half-marathon race pace.

Why does an ultramarathoner need it?

it pushes the anaerobic threshold higher;
it teaches the body to process lactate more efficiently;
it builds speed endurance.

A typical workout: 3–4 times 8–12 minutes with 3–5 minutes of rest. No more than 1–2 times a week, and only in certain phases of preparation. For an ultra, this is about 5% of training time.

4.6. Zone 5 (VO2max): “Afterburner” — at the Limit

Maximum intensity, 89–100% of maximum heart rate. “Pedal to the metal.” Short intervals (3–5 minutes), long rest. The sensations: your “lungs are on fire,” your “legs are falling off,” you want to “die.”

The goal: to boost your VO2max — your maximal aerobic power, the “size of the engine.”

Does an ultramarathoner need this zone? Yes, but in microscopic doses. It's like the afterburner on a fighter jet — powerful, but resource-hungry. 1–2 short sessions per month during the preparation period are more than enough. In the peak phase before the race you don't need them at all.

4.7. The Polarization Principle: 80/20, or “Easy vs. Hard”

Now for the main secret: how do you distribute these zones across your preparation?

The 80/20 rule for the ultramarathoner:

80% of training time — in Zones 0–1 (very easy, aerobic base)
20% of training time — in Zones 3–5 (intense work)
Zone 2 — optional, no more than 10–15% of total volume

The biggest amateur mistake is doing every workout at “medium” intensity (Zone 2–3). That's the “gray zone,” where you:

run too fast to develop fat burning;
but too slow to train your thresholds;
accumulate fatigue without adaptation.

The golden rule: your easy sessions must be genuinely easy (conversation flows freely), and your hard sessions genuinely hard (you can only breathe through your mouth). No “happy medium”!

This is polarized training — the method used by elite endurance athletes. In fairness: rigorous comparisons of polarized and “pyramidal” models don't show an advantage for polarization always and for everyone — but for an amateur stuck in the “gray zone,” shifting toward “easier easy, harder hard” is almost always a step forward.

4.8. The “Glass” Principle: Pour Only as Much as You Can Drink

Training volume is like water you pour into a glass. Pour too little and you won't quench your thirst (no progress). Pour too much and the water spills over the edge (overtraining, injuries, illness).

Your task is to find the “minimum effective dose.” You don't need to train 20 hours a week like a professional if your life, work and sleep don't allow you to “digest” that volume. Sometimes it's better to do one workout less and recover better instead.

Listen to your body. Morning heart rate variability (HRV), sleep quality, appetite, mood — these are all clues. Learn to read them, and you'll find your ideal balance between load and recovery.

You can calculate your zones by heart rate, pace or power in the training zones generator.

In the next chapter we'll talk about how to apply all of this to the realities of running in the mountains and over rough terrain. Because out there, different laws apply!