What happens to your body during high intensity exercise and why they are so effective

What happens to your body during high intensity exercise and why they are so effective


It is a formula that came to the fitness world to stay: high intensity but less time is equal to a greater benefit.

So it has become popular and has become the most fashionable type of training in recent years.

Several studies on the effectiveness of high-intensity interval exercises highlight the benefits they offer to the organism, as well as warn of the risks that occur when doing them, especially if they are not done correctly.

Woman doing exercise
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Image caption It works for a short period of time followed by another recovery period.

But do we know what exactly happens in the organism when we subject it to these explosive and fleeting movements?

That’s what the BBC journalist Max Mosley, who specializes in medical issues and the human body, sought in the Getting fit program .

  • What is an interval training? These are periods of great physical effort (between 80% and 90% of the individual’s maximum heart rate) followed by a recovery period, a sequence that is repeated several times in a session.
  • An example could be 10 speed races in a distance of 20 meters, interrupted by a minute of rest between each of them.
  • The distance, speed and time of recovery may vary based on the state of the person’s shape or the type of sport he practices.
  • In the case of a cyclist, he could pedal at the maximum rate for 20 or 30 seconds, slow down to recover for one minute and then accelerate for another 30 seconds.

Mosley consulted with a group of scientists to show what happens under our skin from the moment it is activated almost to the limit of its physical capacity.

“When we demand the most from our body, the sugar stored in the muscles is released and used to propel the body during exercise,” Mosley explained.

Man doing paddle
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Image caption Because these are very explosive exercises, they require the whole body to be activated.

During the first seconds of the exercise, the body searches for all the sources of energy it has to be able to respond to the effort.

This glycogen allows the combustion that ends up activating the aerobic system.

In the program a volunteer was asked to perform a high-intensity routine on a bicycle, analyzing his glucose levels in the muscle of one of his legs before and after physical exertion.

Dr. Niels Vollaard was in charge of comparing the measurements made through an ultrasound.

“There are fewer dark areas in the muscle afterwards, which means that their glycogen was significantly reduced, down by up to 24%,” he said.

Mosley explains that the body responds to the effort increasing in resistance, stimulating the genes that improves the function of the cardiovascular system and this in turn activates the whole organism.

“All the exercises release one form or another of muscle glycogen, but high-intensity exercises do it more quickly and more effectively,” it was found.

That was only part of the experiment that was carried out with a group of six colleagues from an office who followed a high intensity exercise routine for five weeks.

At the end of the training program, Dr. Vollaard analyzed the state of form of each of them and found that on average they had improved by 11% their physical condition, the highest increase of 14%.

The advantage of high intensity intervals is that because the body is subjected to such a demanding job, the body continues to work after finishing the exercise to try to return to a normal state.

Woman doing push-ups
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Image caption Physical trainers warn that not all people are capable of high-intensity training.

This process is known as homeostasis, which is responsible for maintaining the precise conditions in each of the cells that make up the human body.

And even hours later, in the recovery phase, metabolism is still active due to the impact that high-intensity exercise has on improving insulin sensitivity ,which controls the amount of glucose that cells absorb.

Despite the benefits, Mosley reiterated the warning that high intensity exercise is not suitable for anyone and that those who do not have a minimum physical level or have a medical precondition should refrain from performing them without first consulting a doctor.

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