We've used a lot of specialized terms in this book. Here are the main concepts with plain-language explanations.

Physiological Markers

VO2max (maximal oxygen uptake). The maximum amount of oxygen (in milliliters) your body can use in one minute per kilogram of body weight. Measured in ml/kg/min. The measure of the “size of your engine.” The higher it is, the greater your aerobic potential. Average values for amateur men: 45–55; for women: 40–50. Elite athletes: 70–85+. You can estimate your level in the VO₂max calculator.

VLamax. The rate of lactate production at maximal glycolytic activity. It shows how quickly you burn carbohydrates. Measured in mmol/(L×s). For an ultramarathoner a low value is desirable (0.2–0.4), for a sprinter — a high one (0.6–1.0+). More details in the VLamax calculator.

FatMax. The intensity zone (usually expressed as a heart rate or % of VO2max) at which the body burns the maximum amount of fat per minute. The key marker for ultra distances. It usually lies in the range of 60–70% of maximum heart rate.

LT1 (aerobic threshold). The point at which lactate begins to accumulate slightly, but the body still manages to process it completely. The marker of the upper boundary of purely aerobic work. Usually ~70–75% of maximum heart rate or 2 mmol/L of blood lactate.

LT2 (anaerobic threshold). The point beyond which lactate accumulates faster than it can be cleared. The maximum intensity that can be sustained for a prolonged time (30–60 minutes). Usually ~82–89% of maximum heart rate or 4 mmol/L of lactate. Your 10K or half-marathon race pace. The lactate thresholds calculator will help you determine your LT1/LT2.

RER (Respiratory Exchange Ratio). The ratio of exhaled CO₂ to consumed O₂. It shows which “fuel” you are burning:

RER ~0.7 → pure fat oxidation;
RER ~0.85 → a mix of fats and carbohydrates;
RER ~1.0 → pure carbohydrate oxidation;
RER >1.0 → anaerobic work.

Running Economy. The amount of oxygen (or energy) required to run at a given speed. The equivalent of a car's “fuel consumption per 100 km.” The lower the consumption, the better the economy.

Training Zones

Zone 0 (Recovery). 50–60% of maximum heart rate. Active recovery: an easy walk, yoga, stretching.

Zone 1 (Aerobic base / FatMax). 60–70% of maximum heart rate. The zone of maximal fat burning. The foundation of an ultramarathoner's training (70–80% of the time).

Zone 2 (Extensive endurance). 70–75% of maximum heart rate. Long steady running, marathon base.

Zone 3 (Intensive endurance). 75–82% of maximum heart rate. Half-marathon/marathon pace.

Zone 4 (Anaerobic threshold). 82–89% of maximum heart rate. Threshold work, 10K race pace.

Zone 5 (VO2max). 89–100% of maximum heart rate. Maximum intensity, short intervals.

Recovery and Monitoring

HRV (Heart Rate Variability). A measure of how much the time between heartbeats varies. It reflects the state of the autonomic nervous system. High HRV = good recovery, readiness for load. Low HRV = incomplete recovery, stress.

RPE (Rate of Perceived Exertion). A subjective rating of how hard a workout feels on a scale of 1 to 10:

1–2: very easy;
3–4: easy, you can chat;
5–6: moderate, conversation in short phrases;
7–8: hard, talking is difficult;
9–10: maximal, talking is impossible.

RED-S (Relative Energy Deficiency in Sport). A condition in which you burn considerably more calories than you consume. It leads to hormonal disruption, bone loss, reduced immunity and menstrual cycle disturbances in women.

Nutrition and Hydration

Carb loading. The strategy of increasing carbohydrate intake for 2–3 days before a race to fill the glycogen depots to the maximum. The goal: 8–10 g of carbohydrate per kg of body weight per day.

Glycogen. The storage form of carbohydrate in the muscles and liver. The total store in an average person: ~400–500 g (2000 kcal). Enough for 1.5–2 hours of intense work.

Isotonic (sports drink). A sports drink with a concentration of salts and sugars close to that of blood plasma. It ensures rapid absorption of fluid and electrolytes.

Electrolytes. Mineral salts essential for the functioning of muscles and the nervous system. The main ones: sodium, potassium, magnesium, calcium. At an ultramarathon, sodium is critically important (~1 g per liter of fluid).

Hyponatremia. A dangerous drop in blood sodium concentration (<135 mmol/L). It occurs with excessive water intake without salt. Symptoms: headache, nausea, confusion. It can lead to brain edema.

Trail Running

VAM (Vertical Ascent Meters per hour). The vertical climbing speed in meters per hour. A measure of “mountain” fitness. A good level for an amateur: 600–800 m/hour; for the elite: 1200–1500+ m/hour.

Cadence. Step frequency per minute. Cadence is individual and depends on height, speed and technique: the often-cited 170–180 steps/min is a common reference point, not a universal norm. On descents, cadence usually increases.

Pacing. The distribution of effort over the distance. The strategy of maintaining an even pace (or heart rate) instead of “ragged” running.

Muscle Fiber Types

Oxidative fibers (slow-twitch, type I). Muscle fibers that run on fat, are resistant to fatigue and contain many mitochondria. Ideal for the ultramarathon. Red in color (lots of myoglobin).

Glycolytic fibers (fast-twitch, type II). Muscle fibers that run on carbohydrates — powerful, but they fatigue quickly. Used in sprinting and strength exercises. White in color.

Metabolism

Glycolysis. The process of breaking down carbohydrates (glucose, glycogen) to produce energy (ATP) and lactate. It can proceed with oxygen (aerobic) or without it (anaerobic).

Fat oxidation (lipolysis). The process of breaking down fats to produce energy. It requires a lot of oxygen but yields an enormous amount of ATP. The primary energy source in an ultramarathon.

Mitochondria. The “power plants” of the cells. They produce ATP (energy) from fats and carbohydrates using oxygen. The more numerous and larger the mitochondria, the more enduring the athlete. They grow in response to long, low-intensity training.