A systematic review of 77 studies suggests that while both interval training and continuous moderate-intensity exercise are effective for fat loss, interval training may produce results in a more time-efficient manner. Researchers from Brazil and England conducted the review to identify what type of exercise—continuous moderate-intensity (MOD), high-intensity interval training (HIIT) or sprint interval training (SIT)—is best for weight loss.
The investigators defined MOD as continuous effort at 55%–70% of maximal heart rate. HIIT was defined as intermittent periods of training at 80% of HRmax, and sprint-interval training as intermittent training at an even greater, or “all-out,” effort. Participants were male and female, with mean ages ranging from 10 to 70 years, depending on the study. On the fitness scale, subjects included sedentary individuals all the way up to high-level athletes.
Data analysis showed that all training methods resulted in similar reductions in body fat (3.5%–4.6%), but typical MOD sessions lasted 38 minutes, while HIIT sessions were 28 minutes and SIT were 18 minutes. Authors of the review noted, however, that higher-intensity training may increase injury risk and cardiovascular stress and can present adherence challenges, since it’s less comfortable. Another difficulty in drawing conclusions from the review, according to its authors, is that training protocols varied widely regarding work-to-rest ratios and interval lengths, so no recommendations can be made regarding ideal interval training or MOD protocols.
The researchers recommend that future investigators improve methodological quality, sample size and assessment method to provide more compelling evidence pertaining to specific protocols. Look for the study in the British Journal of Sports Medicine (2019; doi:10.1136/bjsports-2018-099928).