Researchers have been debating this question for decades: When it comes to fat loss, are people better off doing HIIT or traditional cardio?
There’s little doubt exercise in general is great for helping people lose and maintain their weight. “The most successful weight-loss maintainers — those who lose weight and keep it off — often credit a regular exercise regime as a key component to keeping the weight off,” says Shelley Keating, PhD, researcher at the School of Human Movement and Nutrition Sciences at The University of Queensland, Australia.
But while exercise in general can be a helpful aid in weight loss and weight maintenance, surely one form is more effective than others, right?
Before we dive into the research on moderate-intensity versus high-intensity cardio, it may be helpful to clarify between different types of interval training. And, because definitions can vary depending on who you ask, here’s how Keating and her research group define two popular forms of interval training:
This is when you perform 1–4-minute bouts of activity at an intensity equivalent to 80–100% of your maximum heart rate. These intense bouts are followed by lower-intensity recovery periods.
SIT is more intense than HIIT. Here, you alternate 8–60-second all-out sprints (done at 100% intensity) with a short recovery.
These two forms of interval training are typically compared to moderate-intensity cardio (often running or cycling) performed at 50–70% of maximum heart rate.
The findings on cardio and fat loss are mixed. Some studies reveal interval training is more effective than moderate-intensity cardio, while some suggest both forms are equally effective. Still others show moderate-intensity is the better option.
For example, a study in the International Journal of Obesity found that three weekly HIIT sessions helped women lose as much as 7.3 pounds over the span of 15 weeks, while women who performed steady-state cardio gained nearly three pounds during the study.
Meanwhile, a recent review found people lost just as much weight via interval training as they did with moderate-intensity cardio, but only when the volume of training was similar. “As fat loss requires high amounts of energy to be expended, the volume of exercise is important, and therefore only HIIT and SIT protocols, which have equivalent volumes of exercise to traditional training, may produce similar fat loss,” says Keating, who co-authored the analysis.
See, while you burn more energy (Read: calories) per minute during interval training, you may not be able to go long enough to match the overall volume of a moderate-intensity cardio session. And while it’s true you burn more energy after HIIT and SIT than a moderate-intensity workout (known as post-exercise energy consumption, or the “afterburn effect”), the amount is minimal. “The key for fat loss is how much energy you expend with each exercise session,” Keating says.
And finally, a 2014 study published in the Journal of Obesity found interval training led to weight gain.
For the study, 38 inactive adults were randomly assigned to one of three exercise protocols: HIIT, moderate-intensity cardio or a placebo group. After 12 weeks, the HIIT group increased their trunk fat by up to 1.7%, while both the continuous cardio and placebo group saw a decrease in trunk fat (as much as 4.7% for continuous cardio and 1.5% for placebo).
The weight gain in the HIIT group could have happened as a result of compensatory eating (i.e., eating more after exercise), says Keating, who co-authored the study. However, since researchers didn’t track eating behaviors, it’s impossible to say this is what happened. That said, researchers measured calories burned during exercise and found the moderate-intensity group burned about 283 calories per session, while the interval group only burned about 95 calories.
While some doctors, researchers and fitpros worry the all-out intensity of interval training scares off the people who need it most (i.e., the inactive, overweight and/or pressed-for-time), thus making them less likely to stick with it over the long-haul, new research in Medicine & Science in Sports & Exercise suggests otherwise.
Researchers from the University of British Columbia had 30 inactive men and women perform one session of moderate-intensity cardio (prolonged effort at approximately 70–75% maximum heart rate), sprint interval training (“all-out” 20-second sprints) or HIIT (one-minute bouts at 85–90% of max heart rate) on a cycle ergometer in random order on separate days. Then, participants were asked to report whether they had logged any exercise on their own during a four-week follow-up. According to the study findings, 79% of the men and women logged HIIT sessions on their own once the study had ended.
It may sound cliché, but the answer is: The type you enjoy and will commit to in the long-term, Keating says.
Or maybe try both moderate-intensity and high-intensity cardio. After all, you can’t train at high-intensity every day. Plus, some days you may not feel like doing lung-busting intervals, while other days a long, slow cardio session may sound like torture. Not to mention, most researchers and fitness professionals recommend keeping high-intensity workouts at a minimum to avoid injury and burnout.