At first glance, aerobic training looks like nothing more than sweating on a treadmill, but your heart rate zone changes everything. One zone burns fat, another trains the heart, and a third teaches the body to tolerate lactic acid. In this first part, we look at what aerobic training is physiologically and how to make it work for you.
What aerobic training is physiologically
At rest, the heart beats an average of 60 times per minute — genes and training status can shift that number in either direction. When your muscles need more oxygen, your heart rate rises to deliver the blood. Every heart also has a ceiling: maximum heart rate. A simple formula is 220 minus your age, accurate to within +/- 10 beats.
Exercise becomes aerobic when your heart rate rises to about 60 percent of maximum. It’s a light jog, there’s no gasping for breath, and no lactic acid is produced yet. The word itself comes from the fact that oxygen takes part in energy production. Once your heart rate climbs to 70 percent, lactic acid starts to seep into the muscles. This boundary is called the aerobic threshold. The threshold is different for everyone — it depends on genes, training status and how you feel on the day.
Aerobic training in three heart rate zones
Aerobic training splits into three clear zones, each with its own role and its own cost to the body.
Base endurance (60–70%)
Your heart rate stays below 70% of maximum, you feel good, and you can hold a conversation. Energy comes mainly from fat, which is why this is called the fat-burning zone. Blood flows not only through the large vessels but also opens up the fine capillaries — in young people, new blood vessels may even form. No lactic acid is produced at all; on the contrary, acid left over from the previous workout is washed away. If your muscles feel stiff after a gym workout, a short, easy ride on an exercise bike is one of the best recovery remedies.
Speed endurance (70–85%)
Your heart rate is up and you’re breathing hard. Lactic acid is produced right away, but the body can still clear it. Both fat and carbohydrate are used for energy, and the higher your heart rate, the bigger the role of carbohydrates. This is the zone where the body’s ability to “clear” lactic acid improves — a very useful skill in gym workouts, where your body needs to recover quickly between sets.
Maximum endurance (over 85%)
Breathlessness turns into pain, and your muscles fill with lactic acid faster than the body can clear it. Energy comes almost exclusively from carbohydrate. In the 85–100% of maximum heart rate range, it is mainly endurance athletes, hockey players and others whose sport demands acid tolerance who train. The average gym-goer doesn’t need to go there every day. In practice, 85 percent is already counted as maximal — for safety, and because it’s quite close to the average person’s anaerobic threshold.
The role of lactic acid in aerobic training
Lactic acid has a bad reputation, but it is actually the body’s protector. Without it, a person would run themselves breathless and the brain would shut down as soon as blood sugar ran out. The acid gives you a signal: that’s enough, slow down. Listen to that signal and use it to your advantage.
In the gym, producing lactic acid is not a goal in itself. What matters more is faster circulation (the pump), improved nerve signaling (strength) and microtears in the muscle (growth). The more efficiently your body clears acid between sets, the heavier weights and longer sets you can use. That’s a direct route to more effective workouts.
Fat also burns better when the body isn’t acidic. Acid can’t be stored in the internal organs or kept in the muscles for long — it is corrosive. Fat tissue has taken on that role: the body also uses fat partly as an acid dump. If you make your body acidic, your appetite for fat grows, because storage space is needed. If your pH is neutral, however, fat is more likely to be used for energy.
You can check your own pH with universal indicator paper bought at a pharmacy, measuring saliva or urine. The target value is between 7.2 and 7.4, i.e. slightly on the alkaline side. If your reading leans acidic, add more base endurance workouts and more plant-based food to your week.
FAQ about aerobic training
How long should aerobic training last?
A base endurance workout usually lasts from 30 minutes to a couple of hours — the lower the heart rate, the longer the body holds out. Faster-paced workouts are inevitably shorter. The exact duration depends on your goal and your fitness level.
Does aerobic training interfere with muscle growth?
Moderate base endurance training tends to help: capillaries widen, recovery speeds up, and lactic acid leaves the muscles. Daily high-intensity cardio, however, can tax the muscle in terms of energy expenditure. Balance is key.
How do you find your maximum heart rate more precisely?
The formula 220 minus age is roughly accurate, with a deviation of +/- 10 beats. Your real number emerges in a sports lab with a stress test, or by gradually raising intensity while measuring your heart rate. For a beginner, the formula is enough.
Translated from Body magazine; Author: Jukka Harju
Author: Greta
Source: Turg.Fitness.ee
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