3 Problems with High-Intensity Interval Training

The allure of short, intense workouts is obvious. But is High-Intensity Interval Training (HIIT) really the only workout you need for good overall fitness?

Brock Armstrong
6-minute read
Episode #452

I was recently investigating a fancy new stationary bike that came on the market not that long ago. It uses a variation of High-Intensity Interval Training (HIIT). It's a slick-looking bike, which appeals to my fashionista side. It also includes some interesting machine learning, which appeals to my inner nerd. And it boasts some pretty phenomenal health study results, which appeals to my inner coach. But despite all that, I still find myself scratching my head. 

This is where the stumbling block starts for me. The bike's website claims that the device is "clinically proven to give you the same cardio benefits of a 45-minute jog in under 9 minutes, with only 40 seconds of hard work."

Really? On a stationary bike? Where you aren't using your arms at all, your skeleton is supported by a seat, and your legs are only moving through a biomechanically repetitive and limited range of motion? I find that claim dubious at best.

Before we get into some of the problems with HIIT, let's clarify what it is. 

What is High-Intensity Interval Training (HIIT)?

HIIT involves alternating brief bouts of high-intensity exercise (30 seconds to five minutes) with shorter rest periods during a single exercise session. For most people, the allure of this type of training is that it promises shorter workouts, which still provide results that are equal to (or greater than) more traditional moderate-intensity training. HIIT is versatile enough to be used in all types of settings. It also packs a punch that can take some extra time to recover from.

Arguably, the most popular form of HIIT is the Tabata method. I wrote about that in an article called How to Use Tabata Training for More Than Just HIIT Workouts. Although the article you're reading right now may seem like it's putting HIIT down, I stand by my previous claims. Tabata training, if done correctly (and that's a big if), is very demanding. The body responds to the stress of this workout by rapidly increasing its capacity to increase oxygen uptake, which is an important measure of fitness.

As I hinted at earlier, you do not need to do HIIT more often than once or twice per week. Doing it more often than two or three times a week can actually be counterproductive. If you are doing these workouts correctly, your body will need time to recover between sessions. The key to making any interval training effective is in the intensity. Which leads me back to the problems with HIIT.

HIIT Problem #1

Cardiovascular fitness based on one particular activity is not the same as cardiovascular health in everyday life.

Cardiovascular fitness based on one particular activity is not the same as cardiovascular health in everyday life.

In biomechanist Katy Bowman’s book, Move Your DNA, she explains that “cardiovascular health comes when the entire circulatory system is used in a variety of ways to deliver oxygen to 100 percent of all cells of the body.” So, with that in mind, let's think about this bike. A stationary cyclist's cardiovascular fitness may allow them to pump a lot of blood to their legs for several hours (or just a few minutes on this device.) But at the same time, that cyclist's body may be providing lower blood supply to other parts of the body that remain still and supported during this short-but-intense exercise session. And that's a problem. 

HIIT Problem #2

Most people aren't doing it right. And by that I mean they're not working out hard enough.

I just did a search for HIIT and found a list of tips that I think are quite typical. Without pointing any fingers, here's what the website said:

  1. Stay aerobic.
  2. Make it measurable, repeatable, paced, and leave gas in the tank.
  3. Choose an appropriate level that suits your fitness level.

You might be thinking, "OK Brock. These tips seem reasonable. What's the problem?" The problem is that these aren't the same techniques used in the lab where all those amazing (and slightly hard to believe) stationary bike results were seen. To get the results they saw in the lab, each one of the intervals must be done at a maximum effort, and that maximum effort must be achieved immediately—no slow ramping up to max. If the intervals are done even moderately easy, or you take too long to reach that maximum intensity, the molecular changes that result in a large concentration of what is called PGC1a (a key regulator of mitochondrial energy) are diminished.

The problem is that these aren't the same techniques used in the lab where all those amazing (and slightly hard to believe) stationary bike results were seen.

If you don't have enough PGC1a built up in your muscle, your body will not provide the necessary signal to improve your fitness. Building up that extreme amount of PGC1a requires a drastic depletion of glycogen (or storage carbohydrate) in the muscles. To induce that type of state, it takes a "fight or flight" type of sprint. That's the exact opposite of what tip #2 told us, which was to "leave some gas in the tank. "

So, if we follow the hype behind HIIT and also try to rely on it as a way to boost our fitness in only 9 minutes, done a few times per week (with only 40 seconds of hard work) but we also take the advice of leaving some gas in the tank, well, we'd likely be better off going for a walk.

HIIT Problem #3

It shouldn't be done in isolation.

When you read statements like "Implementing our protocol has been independently proven by the American Council on Exercise to smash government exercise guidelines," you could easily believe that riding your fancy new stationary bike, every second day, is all you need to do to be fit. If you've been following me for a while, then you know this is definitely not the case.

Only doing HIIT workouts for exercise is the equivalent of eating only broccoli for all of your meals. Sure, broccoli is yummy and good for you, but you'll miss out on lots of other enjoyable and nutritious foods if that's all you eat.

For this analogy, I am obviously asking you to think of providing movement for your body in the same way that you think of nourishing it with food. Think of HIIT like broccoli—it's a valuable source of nutrients, but it shouldn't be viewed as the one and only nutrition source necessary to be healthy. 

I am not disputing the various scientific studies that show increases in oxygen uptake, drops in blood pressure, and increases in fat oxidation after using a device and protocol like the bike I mentioned earlier. But there is much more to fitness and health than just improving your blood test results. 

There's much more to fitness and health than just improving your blood test results.

As I explained in my article Why Cross-Training Is Essential (and Improves Your DNA), including varieties of movement (or cross-training) in your fitness program allows you to vary the stress placed on specific muscles and your cardiovascular system. It has also been known to reduce the possibility of an overuse or repetitive movement injuries that can come from doing a single sport or a single intensity for every workout.

And how can you stay excited about your workouts if they're always done the exact same way, on the same piece of equipment, in the same location? You can't.

HIIT definitely has a place in my exercise regimen, but it's on an equal playing field with walking, strength training, mobility or flexibility, and recovery days.

How to Use High-Intensity Interval Training Appropriately

To drive this point home even more, a 2014 study about intermittent and continuous high-intensity exercise looked at whether you should mix up your interval training or simply do the same type of HIIT sessions each week.

The researchers had one group of volunteers complete 6 weeks of a high-intensity interval training. On a different day, the same group completed a longer effort of four minutes, which burned the same number of calories as the stop-and-go session. The point of this mixture was to vary the intensity and length of the intervals. After 6 weeks, the researchers measured improvements in the participant's athletic performance by having them go as hard as possible for a specified period of time. Then they measured the outcome and reviewed blood and tissue samples.

Then the researchers did it again, but this time, instead of using stop-and-go intervals mixed with steady continuous four-minute workouts, they only prescribed the continuous four-minute steady-state workouts.

You’ll get better results, avoid injury and burnout, and have a lot more fun if you vary and alternate your movement routines.

Again, the researchers made sure that the four-minute workouts burned the same number of calories as the stop-and-go workouts did, which insured that both groups did the same amount of work.

In the end, it turned out that mixing the stop-and-go efforts with the continuous efforts resulted in greater fitness gains and a slower loss of fitness after the study ended when compared with just doing the continuous efforts.

So, if you are going to do HIIT training (and I do encourage you to), you’ll get better results, avoid injury and burnout, and have a lot more fun if you vary and alternate your movement routines. Your blood test results will thank you and so will your future fit self. 


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All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Brock Armstrong Get-Fit Guy

Brock Armstrong was the host of the Get-Fit Guy podcast between 2017 and 2021. He is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute.