Finding the right exercise routine is a personal journey. Some enjoy the tranquility of solo jogging, while others thrive on the competitiveness of team sports like basketball, volleyball, or pickleball. Swimming offers a fantastic low-impact workout, whereas yoga attracts those who value a slower, more mindful pace.

Regardless of your preferred fitness activity, “the most effective exercise is the one you are willing to engage in,” advises Austin “Ozzie” Gontang, a licensed psychotherapist and head of the San Diego Marathon Clinic.

A rapidly increasing number of individuals are turning to high-intensity interval training, or HIIT. “Its rise in popularity is due to its efficiency, its effectiveness in calorie burning, and its cardiovascular advantages,” remarks Lauren Moen, a certified in-home personal trainer from Seattle, Washington.

While HIIT offers significant benefits, it is important to recognize that it may not suit everyone.

What exactly is HIIT?

Many people mistakenly think HIIT refers to a single type of exercise, like running or jumping rope. In reality, HIIT includes any physical activity you can perform intensely. This can involve activities such as running, swimming, cycling, doing jumping jacks, squats, knee kicks, mountain climbers, or burpees. While these exercises may usually be performed at a leisurely pace, HIIT amplifies intensity. You can also enhance the difficulty of HIIT by using weights or resistance bands.

The key to HIIT is performing intense movements for brief periods, followed by rest intervals, explains Martin Gibala, a kinesiologist at McMaster University in Canada and leading HIIT researcher.

A standard approach might involve one minute of sprinting (or another vigorous exercise) followed by one minute of rest or lower intensity movement. Some individuals prefer doing four-minute cycles of high and low intensity, while others use landmarks to structure their intervals. For instance, one might sprint to a distant tree, then walk to the next tree before sprinting again.

Although the term HIIT has gained popularity since the 2010s, this method has long been utilized by elite endurance athletes, such as middle- and long-distance runners, to enhance performance, states Gibala. While not everyone may be eager to try HIIT, “many fitness enthusiasts are drawn to HIIT for its potential to deliver results with a reduced time investment compared to traditional moderate-intensity exercises.”

Is HIIT genuinely effective?

HIIT stands out for being an exceptionally efficient workout that requires little time commitment. This was illustrated in a 2006 study by Gibala, where he split 16 healthy college students into two groups. One group engaged in moderate stationary cycling for 90 to 120 minutes, while the other group alternated between 30-second bursts of maximum cycling followed by four minutes of recovery.

After two weeks, the first group had completed around 12 hours of moderate exercise, whereas the second group had only done 12 minutes of intense cycling. Remarkably, despite the significant difference in workout duration, the second group saw similar improvements across all fitness metrics as the first group, with even greater muscle growth.

Subsequent research has confirmed similar outcomes, with one meta-analysis revealing that HIIT can enhance blood sugar control, reduce inflammation, and improve muscle structure. HIIT is also associated with brain health improvements, and according to Moen, “it can increase your stamina too.”

I-Min Lee, a professor of medicine at Harvard Medical School, mentions that HIIT is advantageous for lowering heart disease risk and improving body composition. This is attributed to the ability of this workout to burn a significant number of calories quickly while decreasing abdominal fat.

Is HIIT safe?

That can vary. Moen indicates that individuals who are not in good physical shape may struggle to perform exercises with high intensity, potentially leading to injuries. “I would not suggest starting with HIIT for those who do not regularly exercise,” Lee concurs.

The same caution applies to those with existing health issues. “Due to the intense levels of exertion required, I wouldn’t advise this workout for anyone with heart problems unless cleared by a doctor,” she warns.

Gibala notes that the demanding nature of HIIT may be “uncomfortable” for some. However, he emphasizes that “high intensity” doesn’t mean going “all out” or pushing to your maximum. Instead, “vigorous intensity can be relative and tailored to personal ability,” he explains. “For one individual, HIIT might mean brisk walking intermittently, while for another, it could involve sprinting uphill.”