High-intensity interval training (HIIT) describes any workout that alternates between intense bursts of activity and fixed periods of less-intense activity or even complete rest. For example, a good starter workout is running as fast as you can for 1 minute and then walking for 2 minutes. Repeat that 3-minute interval five times for a 15-minute, fat-blasting workout. It sounds too simple to be effective, but science doesn’t stretch the truth. Read on for eight proven benefits of HIIT.