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It is well known that exercise has many health-promoting effects, with improvements of quality of life in a wide range of conditions. Additionally, there is evidence of protective effects against mental disorders, and improvements if used as adjunctive treatment. Generally, it is recommended at least 75-150 minutes of moderate intensity physical exercise per week, although newer guidelines are suggesting even longer times.

In the last few years new approaches to training have appeared, trying to facilitate sports practice in our busy life schedules. One of such varieties is HIIT, that stands for High-Intensity Interval Training.

HIIT is defined as any form of exercise with alternating short bursts of high-intensity exercise (higher than 85% peak heart rate and 80% VO2max). Although we are not going into the many types of HIIT in this entry, they have in common its short duration. Usually a HIIT session can be three times shorter than a traditional Moderate-Intensity Continuous Training session (or MICT).

In our entry we are going to focus on a recent meta-analysis article that has studied the effects of HIIT approaches on health to elucidate if it could be an eligible approach against more traditional practices. Studies with interventions shorter than 2 weeks, or with a frequency inferior to 2 sessions per week were excluded.

From the data extracted in 33 eligible reviews, HIIT participants improved cardiorespiratory fitness, some inflammatory markers and muscle structure when comparing with active controls. The range of benefits was more extensive when comparing with non-active controls, and present across a range of ages going from 6 to 75 years old. Regarding anxiety and depression levels, they improved when compared with pre-training situations (only studied in adults).

Additionally, no acute injuries were reported, and more importantly, adherence rates surpassed 80% in most studies. This high level of adherence is of great interest, as usually sports practice is hard to follow, especially among unaccustomed individuals.

Nevertheless, some adverse effects were also reported with HIIT interventions, but uniquely in patients suffering of cardiometabolic disease, obesity, or chronic obstructive pulmonary disease (COPD). Therefore, the need of more studies on HIIT exercise in these and other diseases.

As for the effects of HIIT on mental health, there were no studies available in people with diagnosed mental illnesses such as major depression, schizophrenia or bipolar disorder, among others. It would be an attractive topic, considering the beneficial effects of HIIT on stress and depressive conditions.



  • The data supports the beneficial effects of HIIT exercise along the lifespan in healthy individuals and those suffering of physical, and probably mental, health disorders.
  • When comparing with active controls, HIIT practice improved cardiorespiratory fitness, inflammatory markers and muscle structure more than continuous training sessions.
  • The best health outcomes were obtained with long-interval (more than 2 minutes), high volume (more than 15 minutes) running regimes, conducted 2-3 times per week, for longer than 7 weeks.
  • Because of its high adherence rates (>80%) and short duration, even as short as 10-15 minutes per session, it could be the exercise prescription for certain individuals, although more studies are needed in patients suffering from several conditions.


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Can high-intensity interval training improve physical and mental health outcomes? A meta-review of 33 systematic reviews across the lifespan.

Martland R, Mondelli V, Gaughran F, Stubbs B

J Sports Sci. 2019 Dec 31:1-40. doi: 10.1080/02640414.2019.1706829.

Photo by Meghan Holmes (Unsplash)

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