Traditionally, exercisers have been told that in order to burn fat, they must exercise in the “fat-burning zone,” or at about 60%–70% of heart rate maximum. However, a recent study in the Journal of Obesity (2012; doi: 10.1155/2012/480467) finds that to optimize fat loss, exercisers must raise their heart rate to levels even higher than that.

The 12-week study included 46 previously inactive, overweight men aged about 25 years. The men were separated into an exercise group and a nonexercise control group. Each participant was tested for resting metabolic rate, body composition and insulin levels. The exercise group met three times per week, during which time the members used indoor bicycles to perform 20 minutes of high-intensity interval exercise (HIIE) training. They were instructed to sprint for 8 seconds, followed by a 12-second recovery, throughout the 20 minutes. As the authors described, “The HIIE workload was set at 80%–90% of each subject’s heart rate peak at a cadence between 120 and 130 revolutions per minute (rpm) and recovery was set at a cadence of 40 rpm.” The participants also completed a 5-minute warm-up and a 5-minute cool-down.

By the end of the study, the exercise group’s absolute and relative VO2 peaks had improved significantly. Total body mass was reduced by 3.3 pounds, and fat mass had decreased by 4.4 pounds. The men also noticed “significant” reductions in abdominal (0.3 pounds) and trunk (3.1 pounds) fat. Interestingly, body mass and body mass index changed very little until after 9 weeks.

“As this HIIE program required minimal time commitment, it has implications regarding subject compliance with exercise interventions,” the researchers suggested. “Thus, physical activity prescriptions [that] require the least effort, while still producing adequate reductions in subcutaneous and visceral fat, are likely to be optimal—and HIIE would seem to fall under this category, as a subject’s total commitment was 60 minutes per week.”