HIIT (high-intensity interval training) involves alternating intense work periods with recovery periods during a single cardio session. HIIT takes less time than traditional cardio but has been shown to cause a longer “after burn” of calories. HIIT can be done on cardio machines or as sprints.
Measuring Aerobic Intensity
When estimating how hard to work during cardio (especially important during HIIT), the most important thing is to be consistent. For simplicity, I recommend using the Rate of Perceived Exertion (RPE) scale for estimating how hard to work. (Heart rate monitors don’t have a great reputation for being accurate, but if you’d like to estimate your optimal heart rate zones go here.)
Rate of Perceived Exertion (RPE)
RPE rates exercise intensity on a scale of 1-10. Most people should exercise below 8-9 for sustained bouts of cardio.
Determining Work and Recovery Periods
Work as hard as you can (“all out”) for a short burst or sprint (around 85% of your max heart rate, or 8-10 RPE). During work periods you can increase/decrease the intensity on your machine by adjusting the resistance level, incline, or both. Just be sure you can easily make adjustments quickly.
Slow down, lower the intensity, and let your heart rate come down to 65-70% of your heart rate max, or 4-5 RPE.
Aim for a 2:1 ratio of work to rest.
What if you’re having trouble recovering between work phases?
If you haven’t been training in awhile, HIIT is something you need to work up to. If you find the recovery period is not long enough to let your heart rate come down to the specified RPE, lower the intensity for the work phase and/or recover 30 seconds longer until you can work up to the specified times/levels. Your endurance will increase over time.