Once Is Enough

High-intensity interval workouts are a love-hate endeavor since the whole point is to exercise uncomfortably hard. The good news is that once a week is enough. A study in Medicine & Science in Sports & Exercise found that one 23-minute HIIT session a week for one month can lower body fat and boost aerobic capacity. In the study, 56 overweight guys did one of five protocols: either a thriceweekly moderate-intensity workout; a HIIT three times, twice, or once a week; or zero exercise. For losing body fat, HIIT is better than moderate intensity, but surprisingly, once-a-week HIIT is nearly as good as three times. Plus, health markers like aerobic capacity and blood pressure also improved for the once-a-week HIIT group. For this to work, you can’t half-ass it—you’ve got to push hard. Try their workout: one minute of shuttle runs at 90 percent of max heart rate, backing off to 70 percent for one minute, and repeating that 11 more times.