The Science of HIIT Training: The Reasons It’s So Effective

Categories: Blog

One of the most common misperceptions about exercise is that you have to spend many hours training to get the best results.

Programs or activities with high intensity interval training (HIIT) can offer many benefits without the need for a lot of time. The benefits include a reduction in body fat percentage, an increase in muscle mass and definition, a reduction in the risk of developing a chronic disease or simply a reduction in stress.

Understanding HIIT

HIIT is a form of cardiorespiratory exercise that alternates between short bouts, high intensity work, and lower intensity bouts of exercise to allow for active recovery.

On a scale of 0 to 10, high intensity can be considered any activity above an effort level of eight, while lower intensity active recovery intervals need to be an effort level of 6 or less. Another way to manage it is that the high intensity intervals develop to the point of not being able to speak fluently.

Rather, recovery intervals have to be long enough to regain control of breathing. HIIT training requires exercises to be performed for short periods of time, ranging from 10 to 45 seconds.

Can be performed with almost any type of exercise equipment, including traditional cardio machines, strength training tools such as kettlebells, dumbbells, medicine balls, or without any type of material.


Helps reduce the risks of developing chronic diseases

HIIT is considered a workout for the heart muscle. High-intensity intervals help the heart be more efficient at moving blood through the body, reducing the risk of developing heart disease.

High intensity work ranges rely on anaerobic glycolysis to produce adenosine triphosphate (ATP), the chemical used to generate energy, from oxygen-free glycogen. Anaerobic glycolysis helps muscle cells become more efficient at metabolizing carbohydrates and helps reduce the risk of developing diabetes.

Finally, the fact that HIIT can help you use a high level of calories, allows you to maintain a healthy body weight and significantly reduce the risk of obesity (Gibala, et al., 2012).

Increased size and definition of muscles

Type II muscle fibers used for anaerobic glycolysis are also responsible for increasing muscle hypertrophy. When type II muscle fibers are constantly required to use glycogen for high intensity exercise, they will adapt by storing more glycogen for future workouts.

Because glycogen molecules cling to water molecules, as muscle cells store more glycogen, they can increase overall (Buchheit & Laursen, 2013).

Muscles will continue to burn calories after training

During a HIIT workout, the muscle will metabolize carbohydrates for fuel, however after the workout, Type I muscle fibers will metabolize fat for energy in the post-exercise recovery period as the body returns to its normal state. normal rest (Buchheit and Laursen, 2013). The neuromuscular system will replace the depleted glycogen and begin the process of repairing muscle proteins damaged during exercise.

Helps increase mitochondrial density in type I muscle fibers

HIIT can increase the density of muscle fibers, improve stroke volume in the left ventricle of the heart, and improve aerobic capacity.

This was previously thought to happen only as a result of slow long distance (LSD) training protocols (Gibala et al., 2012). The benefits of training for an hour can be replicated in an intense training for less than ten minutes. Which leads us to make better use of the time available to train.

Helps raise anabolic hormones responsible for the growth of new muscle proteins

As part of the repair process after HIIT, the body will produce growth hormone, testosterone, and insulin-like growth factor-1 to repair damaged muscle proteins (Buchheit & Laursen, 2013). A HIIT, combined with regular strength training, could help increase the overall levels of these hormones, resulting in an overall increase in muscle mass.

Helps reduce the risk of developing Alzheimer’s or dementia

Brain-derived neurotrophic factor is a protein that helps promote the growth of new brain cells. (BDNF)

HIIT has been shown to have a more significant impact on raising BDNF levels compared to moderate intensity exercise (Szuhany, Bugatti, & Otto, 2015).


HIIT is beneficial, but it can put a great deal of stress on the body. Therefore, it is recommended to perform it two or three times a week with a minimum of 48 hours between exercise sessions to allow a complete replenishment of energy stores and repair the muscle tissue involved. You can exercise the day after a HIIT session, at a lower intensity and use different muscle groups.

You can find this type of program in clubs (HIIT, CrossDir, Bootcamp) and in activities Outdoor (Bootcamp).

Jordi Notario

Co director «Dir Outdoor»