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The afterburn effect: Myth or magic bullet?

afterburn head

The afterburn effect and high intensity training go hand in hand. By following a Freeletics Training Journey, you're benefitting from this curious physiological effect more than most, but why? And how can you optimize it?

Oxygen deficit and compensation

Our body needs oxygen to generate energy – the more work it has to do, the more oxygen it needs. HIIT raises your pulse, respiratory rate, body temperature and metabolism to a very high level over a very short period of time.

How does it work?

It takes a few minutes after starting a HIIT workout until your body is able to use as much oxygen from the air as it needs. Because of this time delay, there is an oxygen deficit. When you finish training, this deficit will be compensated as even more oxygen is absorbed; in fact, more than is actually needed to recover the deficit. You could say that the oxygen debt is being repaid with interest. This is called excess post-exercise oxygen consumption (EPOC).

Even when our breathing has returned to normal after training, cellular respiration continues at full speed. A lot of energy is being used to regulate the many different systems back to their normal levels. In addition, our muscles remain in a heightened state of tension and regenerative processes, such as the replenishment of glycogen and oxygen reserves, are occuring.

During this time, many different processes occur (increased protein synthesis, the recovery of lactate and the repair of the muscle tissue, to name just a few). All of these require a large amount energy, prompting the afterburn effect.

How long does the afterburn effect last?

The more intense the physical stress, the longer the body needs to complete these processes, so the longer the afterburn effect lasts. Although the afterburn effect also occurs with low and medium intensity exercises, it's only really significant at a high intensity level.

The afterburn effect reaches its peak during the first hour after a workout; after this, it decreases exponentially.

Should I try to regulate my training intensity with the afterburn effect in mind?

The afterburn effect is a huge benefit of training. However, it shouldn’t be your goal. The only way to progress continuously and to improve your performance is a combination of different training intensities. The more progress you make, the more intense you can train and the more calories you will burn.

How intense is the afterburn effect?

We need to know the extent of energy expenditure during training to properly judge the impact of the afterburn effect on an individual. This, however, differs from athlete to athlete because of individual differences in gender, age, hormones and metabolism.

Training conditions, sleep, stress and illness also have a direct impact on performance. The highest possible afterburn effect can only be achieved if the athlete really goes to the limits of their performance during the workout.

Measuring the afterburn effect requires complex equipment; for most of us, its impact has to be felt and percieved, not measured.

The afterburn effect - a over- or underestimated symptom?

It is estimated that the afterburn effect, depending on the intensity of the workout, may vary from approximately 5 to 20% of the energy consumed during training. Assuming a workout requires 500 kcal and the athlete has reached the limits of performance (20%), the afterburn effect would amount to approximately 100kcal extra. This corresponds to about one banana. That might not sound like much, but the key difference is that these calories are obtained mainly from fatty acids. As HIIT promotes the afterburn effect more so than most types of exercise, this makes it a highly effective means to lose weight.

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