Workouts that mix up a variety of intense exercises with brief recovery periods in between may help people lose more weight than chugging along at a steady pace on a treadmill or exercise bike, a research review suggests.
Doctors often advise people trying to lose weight to focus on cutting calories and getting more active. But the ideal type and amount of exercise for optimal weight loss isn't clear, researchers note in the British Journal of Sports Medicine.
For the current analysis, researchers examined data from 41 smaller studies that compared weight loss results after at least four weeks of either interval training or moderate intensity continuous training programs, such as jogging, cycling or walking at a steady pace.
Both men and women lost weight and body fat with both types of workouts, regardless of starting weight.
However, interval training provided greater total weight loss: an average of 1.58 kilograms (3.5 pounds) compared with 1.13 kilograms (2.5 pounds) with continuous moderate intensity activity.
"Losing weight is not only about how many calories you burn during exercise, but also how your body reacts during the hours and days after exercise," said senior study author Paulo Gentil of the Federal University of Goias in Brazil.
"We found that interval training promotes higher fat loss and sprints interval training might be particularly efficient at this," Gentil said by email.
Interval training sessions in lasted an average of 28 minutes, compared with just 18 minutes for sprint interval sessions and 38 minutes for continuous moderate intensity workouts.
While the exercise protocols varied, the most common high intensity interval workout alternated four minutes of all-out exercise with three minutes of recovery.
Whether you prefer the all-out nature of interval training or the slow and steady continuous exercise, do what you like. Odds are you'll keep up that habit longer if you do.
The exercise experiments in the study included a total of 1,115 participants and lasted from four to 16 weeks.
One limitation of the study is that the wide variety of interval training programs tested made it hard to determine whether one particular approach might be ideal for reducing body fat or losing weight, the study authors note.
Most exercise guidelines recommend 150 to 250 minutes a week - and up to an hour a day - of moderate intensity aerobic exercise to prevent weight gain or to achieve modest weight loss. Obese people with many more pounds to shed are advised to exercise more than an hour a day, a target few people achieve, researchers note in the British Journal of Sports Medicine.
Exercise has many health benefits, but isn't necessarily risk free, particularly for people who are older or have chronic health problems said Dr. Peter Kokkinos of Georgetown University School and the Veterans Affairs Medical Center in Washington, D.C.
"Too much exercise can result in serious musculoskeletal injuries, cardiac events, including heart attacks and even death," Kokkinos, who wasn't involved in the study, said by email. "The risk of such injuries is extremely low with low-to moderate intensity exercises, but may increase slightly with increased exercise intensities and duration."
Even the higher risk of interval training can still deliver a bigger payoff, said Keith Diaz, a researcher at Columbia University Medical Center in New York City who wasn't involved in the study. People who can't manage interval training all the time may still get some benefit from doing this once a week.
"It is suspected that interval training may lead to more weight loss because it triggers your body to burn more fat in the 24 hours after you exercise," Diaz said by email. "This is because when you exercise really intensely, your muscles use all its energy stores that come from carbohydrates."
But because interval training doesn't burn much fat during the brief bursts of exercise, other, longer workouts may achieve similar results for fat loss, Diaz added.
"Both interval training and continuous exercise generally showed similar benefits for weight loss, so whether you prefer the all-out nature of interval training or the slow and steady continuous exercise, do what you like," Diaz advised. "Odds are you'll keep up that habit longer if you do."