In the previous chapter we compared the body to a hybrid car. Now let's pop the hood and see what “parts” are in there and how they work. Don't worry — you won't need an engineering or medical degree; I'll explain everything in plain language. Understanding these six markers is your key to building smart preparation, not just hard preparation.

2.1. VO2max: The “Size of Your Engine”

Imagine you're choosing a car. The first thing you look at in the spec sheet is engine power, right? VO2max, or maximal oxygen uptake, is exactly that — the “power” of your aerobic (oxygen-based) engine. This number tells you how many milliliters of oxygen your body can “process” per minute for every kilogram of your body weight.

The higher your VO2max, the more oxygen reaches your muscles, and the more energy they can produce. It's like fitting your car with a more powerful engine. Of course, genetics plays a significant role here — some people are born with a sports-car “engine,” others with a family-sedan one. But the good news is that this marker can and should be trained. A high VO2max isn't only about personal records — it's also one of the best indicators of overall health and longevity. So by working on it, you're giving a gift not only to your race result but to your future self.

2.2. Lactate: The “Super Fuel” Everyone Mistakes for “Waste”

Ah, lactate, or “lactic acid.” So many myths and horror stories surround it! “My legs are full of lactic acid,” “I'm all acidified” — who hasn't heard that? It's time to set the record straight.

Lactate is not a “waste product” and not a “poison.” On the contrary, it is a highly valuable energy source! When we run fast, the body breaks down carbohydrates (glycogen) and produces lactate along the way. That lactate is then happily “eaten up” by the heart, the brain and even the working muscles themselves, which extract energy from it.

The problem arises not from lactate itself, but when we start producing it faster than we can process it. Imagine trying to pour gasoline into your tank from a jerrycan faster than it can flow through the neck. Sooner or later the fuel spills over the edge. That “overflow” is what we feel as burning muscles and sudden fatigue.

2.3. Lactate Thresholds (LT1 and LT2): The “Tachometer” of Your Endurance

Our “car” has a tachometer that shows which zone the engine is running in. The lactate thresholds are exactly those marks on our internal tachometer.

LT1 (aerobic threshold). This is the “green zone.” You are running easy and can hold a comfortable conversation. The body runs mostly on fat, and the small amount of lactate produced is immediately recycled. For an ultramarathoner this is the most important point of all. The ability to run at or slightly below LT1 is the foundation of everything.
LT2 (anaerobic threshold). This is the “red zone.” The point beyond which lactate starts to accumulate like an avalanche. You can no longer talk, your breathing falls apart, and your legs are “on fire.” It's impossible to sustain this mode for long. This is your 10K or half-marathon race pace — definitely not an ultra pace.

Knowing your thresholds lets you set up your training zones with surgical precision.

2.4. VLamax: The “Hole in the Gas Tank”

VLamax is a measure of how quickly your body can produce lactate (and, accordingly, burn carbohydrates). If you have a high VLamax, you are a born sprinter. Like a racing car, your body can deliver enormous power within seconds.

But for an ultramarathoner, a high VLamax is trouble. It's like a hole in the gas tank. You burn through your precious, limited carbohydrate stores at a frightening rate even at a relatively low heart rate. Your task is to deliberately “patch” that hole with specific training in order to become more economical.

2.5. FatMax: The “Holy Grail” of the Ultramarathoner

And here is our main goal! FatMax is the intensity zone (most often expressed as a heart rate) at which your body burns the maximum amount of fat per minute.

Why does it matter? By training precisely in the FatMax zone, you teach your body to burn more fat at the same running pace. An untrained runner burns at best 0.3–0.5 grams of fat per minute, a trained ultramarathoner burns 0.8–1.2 grams, and the record values recorded in elite athletes in the lab are around 1.5–1.9 g/min. The difference between “before” and “after” training is two- to threefold: every minute of running, a trained athlete saves noticeably more carbohydrate. Over a 10-hour race that is a decisive difference.

A huge share of your training will be aimed precisely at this:

Finding your FatMax zone.
Using long, low-intensity sessions to “upgrade” it: teaching your body to burn more fat, and to do so at a higher heart rate.

That is the secret of becoming a “fat-burning machine.”

2.6. Running Economy: The “Consumption per 100 km”

The last element — but not the least — is economy. How much energy (and oxygen) you spend to cover one kilometer. It depends on many factors: your running technique, your weight, the stiffness of your muscles and tendons.

You can have a huge “engine” (VO2max), but if your technique is poor and you waste extra energy on unnecessary movements with every stride, you'll be like a powerful SUV with terrible aerodynamics.

Technique work, strength exercises, choosing the right shoes — all of it contributes to better economy. Sometimes, to go faster, you don't need to press harder on the gas — you just need better aerodynamics.

Now that we know the main “parts” of the body, in the next chapter we'll talk about how to put them through a proper “vehicle inspection.”