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To HIT or Not To HIT: High Intensity Interval Training

Thomas (Thom) M. Rieck, MA, CRAT, CSCS
Rieck, M.A., CRAT, CSCS, deep dives into the health benefits of HIIT style exercise and how it will help you get in shape on a tight schedule.
Family Medicine & Primary Care


With high-intensity interval training, there are unfortunately many different ways to feed a cat, just like we do with lots of things in medicine. We take something that should be relatively simple, and we make it as complicated as possible. 

So, if you're not familiar at all with high-intensity interval training, it's essentially a series of times when I work relatively difficult or hard, interspersed by periods of light or no activity. If we can't, we contrast that with a moderate state of exercise where I just hold a specific speed or specific grade, or if I'm using the elliptical at a specific level, and I hold that for a certain amount of time. 

If you've ever done an actual to Tabata style of exercise where you're working for hard, hard, hard for 20 seconds at about 170 percent of your VO2 max, and then intersperse that with about 10 seconds, that workout is not enjoyable at all. 

And unfortunately, what we've done is we've taken that original research that actually was really great, especially for high-intensity speed skaters, and we've applied that to things like yoga, where I'm holding a pose for 20 seconds fall and 10 seconds or relaxation. Now, I've done a lot of hard yoga classes, but never probably at 170 percent of VO2 max. So, it's great, and I still enjoy this movement, but we have to be just a little bit careful. 


I'm going to really kind of focus on the short, high-intensity interval training and then the long heightened sensitivity training. And that's going to be about 90 percent of the VO2 max. And so, if you remember from way back in your physiology class, your VO2 max is the maximum amount of oxygen your body can take in at one time when you're doing an incremental exercise test. 

So, right before you say uncle for that exercise test, you’re at 100 percent there. And so the reason why you can get 180 percent is “Yes, I'm well above that maximum, but I'm doing it for a very short amount of time.” So imagine maybe I'm going to jump on the treadmill and run really hard at 8 miles an hour for 10 seconds. That is something I can actually do. But if you ask me to run for more than a couple of minutes, there's no way I can do that. 


We know that on a time, kind of minute by minute, if I do 30 minutes of HIIT or if I do 30 minutes of moderate exercise, actually the HIIT style training elicits a higher level of cardiovascular death adaptation than kind of steady-state exercise. And it's also very time efficient. So, as we can see there, I need less time to get that same benefit. 


So, of course, all of our patients, the number one thing they say is, “I don't have time to exercise.” Maybe you're thinking about that today. Maybe you don't want to listen to the guy that's gonna talk about pilates later this afternoon. You want to go upstairs and get an exercise session? That's OK with him. It’s very time efficient. So, how do we actually program around that? That's what we need to ask ourselves today. 

And, of course, the reason why we want to really focus on our VO2 max is because it makes life easier. If I have to walk up a flight of stairs, it takes a certain amount of oxygen. If I have a very high reserve, my VO2 max is, let's say 50, and it only takes me 14 milliliters per kilogram per minute of oxygen to walk up those stairs, I've got a very big reserve of that oxygen. But if my VO2 max is relatively depressed, let's say 20, I'm not going to feel so good after I walk up those flights of stairs. 

And so we say that a metabolic equivalencies was about 3.5 milliliters per kilogram per minute is what 1-MET is equal to. Even a 1-MET increase in our cardiovascular health can actually have drastic impacts. For people who are overweight or obese, that's an even bigger jump. 


Now, we can typically see a 1-MET increase in somebody's cardiovascular health and about as little as six to eight weeks of training, about twelve sessions or so. So, it's not something that we need to really look out on the horizon and say, “Well, you have to be doing this for years and years and years before you're going to have a big benefit.” We can actually see that small change relatively quickly. 


So, the reason why HIIT is so hot is this kind of exercise, post-oxygen consumption, also known as EPOC. And, essentially in our exercise, and especially in this high-intensity piece, we build up a little bit of oxygen jet, and we have to pay that back. So, eventually, our body is going to come back and say, “I need a little bit of extra movement calories to return.” And exercise does do a small amount of that oxygen get. But it's not nearly as big as a HIIT-style workout. And so there's a lot of processes that have to happen afterwards before we can recover. 

That is the tune of roughly about 83 calories or so. So, there were some original studies that came out and said, “Oh, you're burning 500 calories after spending 20 minutes in the gym.” And unfortunately, we just haven't found that true. 

But I don't think 83 calories is anything to sneeze about. I mean, that's one and a half Oreo cookies, or one and a quarter bites of Chicago deep-dish pizza. But when you think about, “Bey, let's add that up, maybe I'm doing two-HIIT sessions per week.” It can have a substantial difference on people's waistlines over the course of time. 


So, the other piece kind of coming from this review and analysis is there's a lot of other great things that happen body-wise. I mean, we'd kill for some of these things to be put into a pill form, as Dr. Scale's kind of mentioned. But I want to focus on the enjoyment of exercise. 

So, a lot of, you know, people that we see “I don't like exercise. I don't like going to the gym changing. It's uncomfortable after exercise is something I may know. I'm sweating all over the place.” And so maybe we can kind of reframe that, saying, “Well, you know, it's not going to be as enjoyable as out walking around or eating some pizza. But maybe it's going to be a little bit easier than you spending 35 minutes on the treadmill during the middle part of your day.”


We are working at relatively high levels of exercise, and a lot of this comes from quite a few different researchers in Norway. They took a look at individuals that were doing cardiac rehab and actually found that it's actually a little bit safer than doing moderate, steady-state exercise. You'll notice that's the time is different. So, the moderate-intensity group did 21,000 hours versus 46,000 hours for the HIIT group. And that's simply because, again, it's a little bit more time-efficient. So, it seems to be at least relatively safe. 

There are only nine variables to choose from when we talk about high-intensity interval training, so should be relatively simple when you're thinking about prescribing to your patients, right? Not so much. 


So the first question is, how hard should we actually work? Well, when we review the literature, it seems that we need to be exercising about 90 percent of our VO2 max. So, relatively hard. That's the point where, you know, I'm huffing and puffing. I could maybe say yes or no answer yes or no questions, but for sure, couldn't recite Shakespeare. I'm definitely moving relatively intensely at that portion. 

The gold standard that we'd like to see is actually to refer them to get a VO2 max test. What we found is if we sit across them and say, “Well, I think you're VO2 max si 25, and so, therefore, here's where your heart rate should be,” and so forth. We have a tendency to have big variability in that and actually could be potentially detrimental. So, the gold standard is really to send somebody for a cardiovascular evaluation, get those numbers, and then prescribe off that. 

What we did find, though, is actually utilizing the Borg scale and having people exercise to the very hard to hard level gets them relatively close. So, I just said the gold standard is you'll get a test, but we don't want to guess at all when it comes to heart rates or prescribing off VO2 max. We'll let that kind of internal governor actually take over. 


This is just a study that took a look at people spending different amounts of time, working in that hard to very hard area, and actually listening. About 90 percent is what we're looking for when it comes to how difficult we are. So, again, we can think about how much time do I actually need to spend working hard and then relaxing? There's 30 seconds on, 30 seconds off. Maybe I want to do two minutes of hard stuff and two minutes easy. 

It seems that the longer intervals and the two minutes to kind of four-minute realm are actually better. And this is actually the 81.8%, the 92 and 93. This is the amount of time that the individual spent at or above 90 percent. We kind of missed the mark a little bit on that one-minute hard, one-minute easy area where I'm doing that work and recovery zone. And so, again, it seems that we need to have about two minutes to four minutes of hard to easy. 


There's also some relatively new research coming out of Sweden that took a look at if I kind of bump up a little bit more in the first kind of 30 seconds to 1 minute and then back down a tad bit, actually, you’re going to spend more time at or above that 90 percent of VO2 max. 

So, in this instance here, we are running at seven miles an hour for a minute and then going back down to six miles an hour. And I think, from a psychological level, a lot of people that's something that's tangible say, “Well, I can do something for two TV commercials. It's only going to be a minute long. I can do that.” And then back it down before I come into my active recovery.


I know I have to be at 90 percent. And I got to be for somewhere about two to four minutes on that hard intensity piece. And the research is, unfortunately, kind of still out when it comes to how many times I actually need to do this. It seems like it's around 4 to 10 repetitions. And again, when we're getting up into that ten or twelve or fifty different repetition pieces, I've lost a lot of that benefit of doing sensitivity training in terms of time. 

Now, my exercise session is taking 45 minutes or an hour. And you're not listening to me because I just told you I don't have that much time to actually devote to exercise. So, can I get four rounds of that in and have it actually an effective cardiovascular intervention? I think so. I definitely think so. 


We know for that kind of sprint-style or Tabata style of exercise that you generally want to stop and recover. But for these two minutes and four minutes, for exercise bouts in that recovery, it seems like we actually want to stay moving. And if we do stay moving, whether it's walking slow on the treadmill or maybe even jumping off, moving around from outside, biking hard, biking easy, etc. I can spend more time when I'm actually in that high intensity piece at or above that 90 percent VO2 max area. 

So, we want to say about 50 percent of VO2 to kind of our lactate threshold. That's that area we want to be in. And to quantify that for you and your patients, you and I could have a conversation at that. Again, we probably couldn't recite Shakespeare, but we could have a conversation between each other if we were exercising. 


And the final piece is how low can I actually go? I'm still a little apprehensive about working up in those high levels. So, this group actually took a look at individuals, and what they had them do is 70 percent of this VO2 max during those high-intensity interval portions and down to as low as 40 percent in the recovery. They worked three minutes hard and three minutes easy. Contrasted with people that did 60 minutes of exercise at 55 percent. So, an easy conversation pace. 

And what we found is, even though we weren't getting up into those 90 percent or above, we still saw a 16 percent improvement in VO2 max, decrease in our overall fat mass, and some great changes when it comes to our glucose. 


HIIT is wonderful. Improves our cardiovascular fitness short amount of time, burns calories, which is something that people are always really focused on. It even burns calories after that exercise when you head back to your desk. 

We want to be pushing pretty hard. That kind of very hard region. Get to the point where we're breathless about a 14 to 17 on that Borg Scale. If you're familiar with that, get to the point where it is a little uncomfortable, and we want to do it for about two to four minutes. We have about two to four minutes of active recovery where I drop that intensity down on the treadmill, or I'm outside, wherever it may be. And we want to get about 4 to 10 repetitions in. And that seems to actually have enough time and enough work to actually elicit all those wonderful things that we're gonna get from high-intensity interval training.

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