Active Voice: HIIT in the Real World – Effective, but Not for Everyone?

By Melyssa Roy, MBChB, MMSc

Melyssa Roy, MBChB, MMSc
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily represent positions or policies of ACSM.

Melyssa Roy, MBChB, MMSc, is a public health medicine trainee and researcher at the University of Otago in Dunedin, New Zealand. In her recent research, she examined the long-term effectiveness of recommending novel exercise and dietary interventions such as high-intensity interval training, intermittent fasting and paleo diets in unsupervised settings.

This commentary presents Dr. Roy’s views on the topic of a research article that she and other colleagues authored. Their research article appears in the September 2018 issue of
Medicine & Science in Sports & Exercise® (MSSE).

Physical activity improves all health outcomes but achieving sufficient amounts of regular exercise is difficult for many people—especially for those who are overweight. Adherence to ACSM exercise guidelines, i.e., 150 minutes per week of moderate intensity activity, is not often attained. Alternatively, vigorous activity of 20-60 minutes duration undertaken three times weekly is recommended. High-intensity interval training (HIIT), defined as short bursts of intense exercise, may provide yet another effective means of achieving the desired health objectives. HIIT is known to be effective in laboratory settings, improving both cardiorespiratory fitness and metabolic outcomes, and it also may improve weight loss. However, it is unknown whether people can adhere to this kind of exercise—in the real world and over the long term.

In our study, as reported in the September 2018 issue of MSSE, 250 overweight adults participated; as subjects, they could choose to undertake 30 minutes of daily moderate exercise or try shorter sessions of HIIT thrice weekly. HIIT was well-accepted, chosen by 104 people. HIIT participants received a single HIIT training session during which they were shown how to exercise at the target intensity and educated about how to achieve HIIT independently. They could perform HIIT using any type of full-body exercise such as running, stairs or by use of exercise equipment, and a range of protocols were recommended. Intervals could range from 20 seconds to four minutes in duration, with a recommended intensity of 8-10 on a 10-point Rating of Perceived Exertion scale. Weight loss, body composition, fitness, amounts of physical activity, adherence and metabolic markers were measured over 12 months.

After one year, there were no differences in outcomes between those who chose to do HIIT or those who opted for regular exercise programs. We did not find any overall benefit to weight loss or fitness in the HIIT group, as compared to the regular exercise group. The absence of differences between the groups for those latter outcomes most likely was due to low adherence in the HIIT group, which dropped rapidly after three months. However, those who chose HIIT did not become less active overall compared with the standard group so, importantly, the recommendation to undertake the much shorter duration HIIT did not lead to a decrease in overall physical activity levels.

A sub-analysis of the 23 percent of people who successfully adhered to regular HIIT over 12 months showed that they were more likely to be male, and that they achieved greater weight loss, visceral fat reduction and improved glucose control as compared with those who didn’t continue with HIIT.

The findings of our study suggest that recommending HIIT as an alternative to standard exercise will not be effective for all people. As with other forms of exercise, adherence to HIIT remains difficult, despite being more time-efficient. Without ongoing support or structured programs, adherence to HIIT is hard. However, a proportion of people will respond and benefit from this type of exercise, so it is suitable to be offered as part of a range of exercise options. Further work is needed on how best to support people to stay active, whether that be in HIIT programs or other types of exercise.