March 10, 2026, 11:16 am | Read time: 9 minutes

Imagine you have to run up a building to the 10th floor. If you walk up the stairs at a leisurely pace, you have enough time to use oxygen—it’s like aerobic exercise. But if you sprint to the top, you run out of oxygen, and your body has to draw on emergency reserves—that’s anaerobic training. Knowing the relationship between aerobic and anaerobic energy production helps endurance and strength athletes to control their training, maximize their performance, and efficiently avoid fatigue.

Aerobic and Anaerobic Metabolism Run in Parallel

The two terms aerobic and anaerobic are related to the metabolic processes in our body: aerobic processes are those that take place with oxygen, while anaerobic processes are those that take place without oxygen.

This distinction is particularly relevant during training. This is because our metabolism works at full speed to generate energy, especially during sport. There is often talk of a threshold at which the body “switches” from the aerobic to the anaerobic metabolic range. However, it’s not quite that simple: in humans, aerobic and anaerobic metabolic processes run in parallel in the body—even in a state of absolute rest.

Strictly speaking, there is no purely aerobic or purely anaerobic training zone. However, knowledge of these two metabolic processes is still extremely helpful for athletes. At best, you know the ratio of aerobic and anaerobic metabolic processes that take place individually during training. To this end, sports scientists analyze when and to what extent the body gains energy primarily through oxygen (aerobic) or without oxygen (anaerobic).

How Does It Help Me to Know Whether I Am Training Aerobically or Anaerobically?

Aerobic training mainly improves our cardiovascular endurance, while anaerobic training mainly increases our muscle strength. A better understanding of metabolic processes helps to control training in such a way that acidosis is avoided. If you know when your body switches to the anaerobic zone and tires more quickly, you can adapt your training plan and competition strategy accordingly. The benefits of knowing about aerobic and anaerobic training using the example of runners:

• Runners, for example, can specifically work on their anaerobic threshold to increase their performance.
• Long-distance runners primarily train their aerobic capacity in order to provide energy efficiently for as long as possible.
• Sprinters make greater use of anaerobic processes for maximum performance over a short period of time

What Happens When the Body Produces Lactic Acid?

To determine the ratio of aerobic and anaerobic processes during training, lactate is measured. “Lactate is the anion of lactic acid and is produced as a waste product during anaerobic metabolism when the body converts sugar into lactic acid,” explains medical doctor and long-distance runner Dr. Paul Schmidt-Hellinger. To find out when the body switches from the predominantly aerobic to the anaerobic range, the increase in the lactate level in the blood is measured. Lactate, the salt of lactic acid, is already present in the human body. Its content is measured in millimoles per liter (mmol/l).

Aerobic Threshold

The physician from the Department of Sports Medicine at Charité Berlin explains the aerobic threshold as follows: “The basic level of lactate in the blood is between one and two millimoles. The aerobic threshold describes the point at which the lactate level in the blood exceeds this value for the first time.” This value then indicates the personal aerobic threshold.

Anaerobic Threshold – “Lactate Steady State”

In contrast to this is the anaerobic threshold: according to the doctor, this is reached “when the lactate level has exceeded the aerobic threshold by at least 1.5 millimoles.” Experts call this point the “lactate steady state.” Put simply, this means that lactate formation and lactate degradation are still just in balance with each other. If you continue to increase the physical exertion, the lactate level rises faster and faster from this point onwards. This leads to exhaustion.

Also interesting: What the VO2max Value Can Reveal About Your Endurance

Why Lactate Had a Negative Image for a Long Time

Lactate was long considered to be detrimental to performance because it was associated with muscle fatigue. The foundation for this theory was laid by biochemist Otto Fritz Meyerhof, who researched glycolysis and lactic acid formation in the 1920s.¹ Schmidt-Hellinger explains the reason for this misconception as follows: “Lactate was often confused with lactic acid itself and was therefore held responsible for over-acidification of the muscle.”

Lactate Shuttle Theory

Today, we know that lactate is not just a “waste product” but plays an important role in energy metabolism. George Brooks is regarded as the savior of lactate’s bad reputation. He put forward the “lactate shuttle” theory in 1985. This theory states that there are two mechanisms by which lactate can be metabolized without entering the bloodstream. In the “intracellular shuttle,” lactate produced within the same cell is shuttled into the mitochondria via a shuttle mechanism. In the “cell-cell lactate shuttle,” the lactate accumulated there is transported to another muscle cell with a higher aerobic potential that is suitable for breaking down lactate. There is no measurable increase in lactate levels outside the muscle in both processes. If the muscle can no longer break down the lactate, it is shifted into the blood. Now it is measurable.²,³

“On the contrary, as an anion, lactate can even intercept the accumulation of acid in the muscle,” says Schmidt-Hellinger, explaining the factor that played a key role in “saving the honor” of lactate. All in all, the muscle naturally over-acidifies during highly anaerobic exercise,” the physician clarifies.

How Can I Determine My Aerobic or Anaerobic Threshold?

The so-called step test is typically used to measure lactate during exercise. “As the name implies, the test is carried out in stages. The athlete is made to run at different speeds, such as four, six, eight, ten, and twelve kilometers per hour for three minutes. After each stage, there is a thirty-second break, and a small amount of blood is taken to determine the lactate level,” explains Schmidt-Hellinger.

The heart rate is also measured. According to the physician, this value can provide the athlete with information on the approximate heart rate range they should use as a guide during training in order to train either aerobically or anaerobically. “However, you have to bear in mind that the heart rate is not a completely reliable value for determining the aerobic and anaerobic range,” Schmidt-Hellinger qualifies. The heart rate often also depends on external factors, such as the outside temperature. It can also fluctuate greatly.

Also interesting: Why Blood Sugar Levels Can Rise During Sport

How Much Does a Lactate Test Cost – and Do You Have to Pay for It Yourself?

Such a sports medical lactate test can be very useful for athletes who are working towards a certain goal. Many health insurance companies even cover up to 90 percent of the costs. Schmidt-Hellinger recommends enquiring directly with your own health insurance company. The Department of Sports Medicine at Charité Berlin offers a lactate measurement as part of a sports medicine check-up. According to Schmidt-Hellinger, it costs around 150 euros.

Also interesting: Are There Health Insurance Companies That Cover the Costs of Going to the Gym?

More on the topic

Fitness Trainer Recommends Light Cardio After Strength Training–Here’s Why

Expert Explains No Energy? Possible Causes and How to Boost It

Can You Feel Whether You Are Training Aerobically or Anaerobically?

The change to the anaerobic range can best be determined by subjective sensations, such as the feeling of having to gasp for air and the onset of exhaustion. According to Schmidt-Hellinger, there are no clear physical signals that indicate whether you are training aerobically or anaerobically. However, the so-called “talking test” is helpful. “If you can still talk to your running partner during training, for example, you are most likely training in the aerobic zone,” says the doctor. However, if you are still so fit in terms of breathing that you could theoretically even sing, there is no training effect.

When Should You Train Aerobically and When Anaerobically? The Expert’s Advice

According to Schmidt-Hellinger, whether you should train aerobically or anaerobically depends on your personal training goal. If you want to improve your own aerobic or anaerobic threshold, the doctor advises training in the moderate anaerobic range, thus providing a gentle training stimulus. “Of course, you shouldn’t overstrain your body, but you should still give it a little incentive. This is the only way to achieve a training effect and improve endurance.”

You can follow the rule that around two-thirds of training should take place in the aerobic to very low anaerobic range, and one-third should actually take place in the intensive anaerobic range. It is also important to take breaks of around 48 hours between training sessions so that the body can regenerate and adapt to the training stimuli.

Extra Tip for Strength Athletes

However, according to Dr. Schmidt-Hellinger, anyone who does weight training and wants to build up as many muscles as possible should mainly focus on anaerobic strength training—in other words, go where the muscles burn. “This is where maximum strength training is important. The training stimulus must therefore reach muscular exhaustion in order to achieve an effect,” explains Schmidt-Hellinger. Additional high-intensity endurance training is not beneficial. “Otherwise, the training stimuli compete with each other and block each other.” As a strength athlete, endurance training should take place in the “relaxed” aerobic range as a warm-up and cool-down.