High Intensity Interval Training (HIIT) has been a hot fitness topic for a while now. Numerous studies have shown the benefits of short bursts of training at high intensity. This makes for catchy headlines and appealing claims for quick workouts and reduced training times (a few minutes a week?) but one reality that often gets lost in the hype is the relationship between rest and intensity.
HIIT is typically written as work time periods and rest time periods. This is sometimes written as a ratio (e.g., 2:1) or, more often, in actual time (e.g., 30-15 meaning 30 seconds of work to 15 seconds of rest which is an example of a 2:1 ratio). The only HIIT timing with a cool, widely-recognized name is "Tabata" which refers to a study in 1996 led by Dr. Izumi Tabata that used 20 seconds of work with 10 seconds of rest for 8 rounds for a total of 4 minutes (often referred to as the "Tabata protocol").
What often gets lost is the level of intensity. In studies, this is usually measured as a percentage of VO2 Max although some use a simpler percentage of maximum heart rate (MHR). The simplest measure is Rate of Perceived Exertion (RPE) which has the exerciser self-assess the intensity level.
The problem arises when people sacrifice intensity for shorter rest periods. Take, for example, the "Insanity" workout program, which says:
You work flat out in 3 to 5-minute blocks, and take breaks only long enough to gulp some air and get right back to work. It's called Max Interval Training, because it keeps your body working at maximum capacity through your entire workout.
Sounds great! Except you can't work at "maximum capacity" for 5 minutes or even 3 minutes. The current world record for the 100 meters sprint is 9.58 seconds, the 200 meters record is 19.19 seconds (almost exactly twice the 100m time although there's a running start into the second 100 meters), the 400 meters record is 43.18 seconds, the 800 meters record is 1:40.91 (or 100.91 seconds) and the 1600 meters (1 mile) record is 3:43.13. If the human body could work at "maximum capacity" for 3 minutes, the 1600 meters record would be about 2:40.
One could try to argue that the term "maximum capacity" is used as the maximum a person can do for the time; e.g., the most work a person can do for 3 minutes. But of course, that's nonsense, as it renders the phrase meaningless. Why not go at "maximum capacity" for 20 minutes and skip the breaks altogether?
The Insanity program is hardly alone. "Tabata" is used to describe all sorts of activities that are not high-intensity. There are even "Tabata" warm-ups! These are not warm-ups for Tabata protocol workouts but warm-ups with 20 seconds of activity followed by 10 seconds of rest repeated 8 times. Heck, why not Tabata TV watching? 20 seconds with eyes open, 10 seconds closed. It's ridiculous, as is the notion of doing two "Tabatas" back-to-back. The Tabata study used supra-maximal intensity (170% of VO2 Max). In other words, it was really freakin' hard.
And that leads to the point of this post. (You knew there was one, right?) And that is:
There is an inverse relationship between intensity and rest.
If you want to do intervals at a high intensity, you need to rest appropriately between intervals. To some extent, conditioning can reduce required rest times. An out-of-shape person will require more time to recover from a high-intensity work interval than a fit person. But this doesn't scale. For example, in weightlifting, the best lifters need more time to recover between lifts because they're able to do more work (lift more weight for more reps) than an inexperienced lifter. We see the same thing in wapping, where an experienced person can hit Muay Thai pads much more forcefully than a beginner.
Or ask an Olympic 200-meter sprinter to run another race after just 10 seconds of rest...and keep doing that for 8 races. That would be like a "Tabata" workout except that every race after the first would take longer than 20 seconds (eventually a lot longer), and making it through all 8 (without pacing) would be like a near-death experience (or living with cats).
Recently, "Rest-based Training" (RBT) has gained some popularity. It's a "new" approach to training whereby you can rest as much as needed in order to perform the next exercises. While hardly a new or radical concept, it did fly in the face of the common personal trainer practice of recommending fixed rest periods for clients. This can still sort of work if the client reduces the intensity of the exercise. But then you lose the benefits of intensity, and at some point you wind up doing the TV-watching workout (which, of course, is not a "workout" at all). Fixed rest periods can still work well when they are tailored to the individual, and resting until ready is common practice amongst experienced weightlifters. RBT can be useful for beginners. The important thing (to this post) is that it acknowledges the inverse relationship between intensity and rest.
HIIT is an excellent training method when done correctly, which means with high-intensity. (It's in the name!) And that means using adequate rest periods.
Be seeing you.
-gary