Study: Moderate Exercise Safer, as Effective as HIIT

Popular high-intensity interval training programs may not be all they're cracked up to be, according to research published this summer by MDPI, an academic journals clearinghouse.

As reported by Folio, HIIT is a circuit-based exercise program in which participants complete a series of weightlifting and cardio-based exercises in four-minute sessions with two minutes of rest in between exercises over a 20- to 30-minute period. Each session traditionally encourages participants to complete the highest amount of work possible within the set time. 

According to University of Alberta exercise physiologist Michael Kennedy, the type of all-out exercising demanded by HIIT, CrossFit and other forms of functional fitness training comes with a number of health risks.

“Physical injury is probably most associated with functional fitness training risks, because people ignore the pain signals in pursuit of going all out for prolonged periods of time,” Kennedy told Folio. “It is also known that intense-type exercise, like that done in this study, increases illness risk due to decreased immunity.”

Kennedy noted that the extreme fatigue that can come with these types of all-out workouts can negatively affect people’s emotional state, which is counterintuitive to the positive psychological benefits usually associated with exercise.

For the study, Kennedy, Ph.D. student Joao Falk Neto and colleagues at the Universidade Católica de Brasília had eight participants who regularly engage in functional fitness training repeat the same circuit-based workout program — once at maximum intensity and once at a more moderate intensity.

Moderate intensity is defined as a 6 out of 10 on the Rate of Perceived Exertion Scale (RPE) — where a 1 is very light, 6 is on the higher end of strong, and 10 is considered all-out.

The researchers found that while the overall repetitions in the all-out sessions were higher, the majority of the work was done in the first two four-minute sessions. By the time the all-out group got to the third and fourth sessions, they were completing nearly the same amount of reps as the lower-intensity group.

Said Falk Neto, “The data showed exercising at an intensity level of 6 enabled you to still reap the positive benefits of the activity while not exhausting you so much that you are not able to sustain this level over the course of an individual session or over time with multiple sessions.”