So What Is HIIT?
HIIT is High-Intensity-Interval-Training. Ok, so what does that mean? HIIT is simply the process of going all out, your maximum heart rate, your red-line, an RPE of 9 or 10, however you want to quantify or qualify your maximum exertion, for 30-120 seconds and then allowing your body to recover for 60-120 seconds. You do this for 5-15 intervals in one workout session. Some studies have shown for advanced athletes that a 2:1 high-intensity to rest ratio is most effective. This ratio is not for beginners.
How Does HIIT Work?
You definitely want to make sure that you've warmed up appropriately before beginning a HIIT workout. For the sake of argument, let's say you're on a health-club-quality treadmill (more about why this is important later). You'd want to warm up at a comfortable pace and elevation for perhaps 3-5 minutes. Once warmed up, you begin the HIIT part of the workout. Your first few high-intensity intervals will be slightly lower at a rate of perceived exertion (RPE) of perhaps 7 out of 10. If your first interval is at an RPE of 10 you may not have enough gas in the tank to complete all the intervals in your workout. Don't worry about not starting out at your absolute max, you'll get there in interval 3 or 4 through the rest of your workout and it will be HARD. Keep that in mind, this is a very difficult workout. Best to only do it 2-3 times per week.
Why Does HIIT Work So Well?
The reason that HIIT works so well is that you are able to get in an overall amount of red-line training time in one workout that you would otherwise not be able to constantly sustain. If you were to go out, after a proper warmup, with the intent to sprint for as long as you can, you might be able to sustain your top speed for perhaps up to 2 minutes. That would be a mighty short workout. By incorporating intervals of high and low intensity, you might get 10, 15 or even 20 minutes at your sprint pace in one workout.
So What Do They Experts Say About HIIT?
Numerous studies have shown immense benefits to HIIT. A Jan 2007 Journal of Applied Physiology study by Talanian et al reported that 7 HIIT sessions over 2 weeks "induced marked increases in… fatty acid oxidation during exercise in moderately active women." A 2010 British Journal of Sports Medicine study by Upadhyay et al reported more than double the improvement in VO2 max (an indicator of fitness level) in a group of high school age males undergoing HIIT training for 6 weeks versus a second group training at a slower and steady pace. The really interesting part of the Upadhyay study is that the HIIT group worked out for a total of 24 minutes 3 times per week = 72 total minutes per week. The steady state group worked out 5 times per week for 60 minutes per session = 300 minutes per week. HIIT allows you to get fitter, faster, while spending less time exercising. What's not to like?
So Why Is HIIT Better On Commercial Machines?
You can, of course, do HIIT outside on a track, on a bike, or even swimming. However, if you are working out indoors, let's say, on a treadmill, you'll want to be on a commercial-grade machine. One primary reason is the rapidity of the speed changes. On a commercial treadmill, when the runner changes the speed setting, it almost instantly goes to the selected speed. On a residential-level treadmill, the runner may have to wait for 20, 30 and even 60 seconds for the speed to change. As you can see, that creates a big problem for HIIT. Why does it take so long for speed changes on a residential treadmill? A variety of reasons but primarily due to motor horsepower, flywheel size, roller size, the speed sensor and controller and some other factors.
At the end of the day what really matters is that when you are doing HIIT properly, you should be at your limit at the end of one of the high-intensity intervals. So you want that speed to decrease immediately to allow for your recovery to begin. You only have a limited time to recover so you don't want to spend that time waiting for the treadmill to slow down. Conversely if it takes 30-60 seconds for the machine to speed up again, you're not getting as effective of a HIIT workout as possible.