How To Do High Intensity Interval Training Correctly

Most workouts labeled “HIIT” are really just hard interval circuits and that one mix-up can be the reason you feel exhausted but don’t see the fat loss, power, or muscle definition you were promised. We get specific about what high intensity interval training actually is: near maximal cardiovascular effort with recovery that’s long enough to repeat that same max effort again. If you can’t reproduce your output, it’s a sign your rest is too short or your intensity isn’t truly high. 

We are joined by Heather Flebbe, an exercise physiologist, a local studio owner at FitFix, and college professor, to cut through misinformation with simple, practical exercise science. We talk about why real HIIT recruits fast twitch muscle fibers, how it supports performance and muscle definition, and why the metabolism boost (EPOC or the afterburn) depends on how close you get to peak intensity. Heather also shares a clear guideline for frequency: one to two HIIT sessions per week, plus the recovery habits that make those sessions count, including hydration with electrolytes and refueling with carbohydrates and protein. 

We also dig into programming details most people never hear, like work-to-rest ratios that can range from 1:2 to 1:8 depending on interval length, and why longer rest can actually create better training results. You’ll learn how to use waking resting heart rate to gauge recovery, why recovery heart rate is a meaningful marker for longevity, and how training your body to spike stress and return to baseline is part of becoming more resilient. And yes, we address the cortisol fear head-on with a science-based perspective that puts context back into the conversation. 

If this helped you rethink your HIIT training, subscribe to Words of Wellness, share it with a friend who loves “HIIT” classes, and leave a rating and review so more people can find accurate, usable wellness guidance.

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Transcript

Why HIIT Needs More Recovery

SPEAKER_01 0:00

So I would say one to two days per week is max because I really want you in those two workouts, I really want you to go to your max effort. So if you truly do that, you really need time to adapt and rebuild and repair, recover, replenish, hydrate with electrolytes, give yourself carbohydrates and protein, yes, carbohydrates, especially after a HIT workout, and to not stress and overtax your physiological system.

Meet Heather And The Mission

SPEAKER_00 0:33

Do you get confused by all of the information that Babar does every day on ways to improve our overall health and our overall wellness? Do you often feel stuck, unmotivated, or struggle to reach your wellness goals? Do you have questions as to what exercises you should be doing? What foods you should or shouldn't be eating? How to improve your overall emotional and mental well-being? Hello, everyone. I am so excited to welcome you to Words of Wellness. My name is Shelly Jeffrey, and I will be your host. My goal is to answer these questions and so much more. To share tips, education, and inspiration around all of the components of wellness through solo and guest episodes. With 35 plus years as a health and wellness professional, a retired college professor, a speaker, and a multi-passionate entrepreneur, I certainly have lots to share. However, my biggest goal and inspiration in doing this podcast is to share the wellness stories of others with you, to bring in guests who can share their journey so that we can all learn together while making an impact on the health, the wellness, and lives of all of you, our listeners. The ultimate hope is that you leave today with even just one nugget that can enhance the quality of your life, and that you will, we all will, now and into the future, live our best quality of lives full of energy, happiness, and joy. Now let's dive into our message for today. Hi, my friends. Welcome back to Words of Wellness. My name is Shelly, and we are so happy to have you here. And I am really excited for my guest today. And I have had her on before because she is a wealth of knowledge, and I just love having conversations with her. And she is going to share with us all today some really important information about how we are exercising, and especially when it comes to doing our interval training, specifically HIIT training. So, Heather, she is an exercise physiologist, and she is the owner of a local studio here called Fitfix, and she is also a college professor. So welcome, Heather.

SPEAKER_01 2:53

Thank you. Thank you for giving me an opportunity to talk about all my favorite exercise physiology topics.

SPEAKER_00 2:59

Absolutely. I love it. I love to be able to have you share, and I think it's so important to get the important and accurate information out to our listeners because that's really that's the whole goal, right?

SPEAKER_01 3:16

Yes. That was my main mission when I got my degree in exercise physiology. My mission was to put out the truth about exercise science, food, fat, fitness, everything, because there's so much misinformation out there. And I hope to clarify with regards to HIT today.

SPEAKER_00 3:35

Yeah, and I think it's so important because we've we've had some conversations about it. And I mean, you even gave me some great tips for me personally. And I mean, you and I have both been in this industry for for so many years. And so I love not only learning new things, but being reminded of what is accurate and what works. And I think it's just an important conversation to continue to have so that people can be getting the results that they are striving for and really be the healthiest that they can be in doing things the right way. So I'm excited to dive in. Yes.

What HIIT Is And Is Not

SPEAKER_01 4:14

Yes. I wanted to talk about what HIT is and what HIT is not, because HIT is probably the most misused term in fitness. And I want to clearly define it for people. And I also want to cover some misinformation or some fear about HIT and cortisol. So what HIT is, why we do it, how to do it correctly, and when to do it, and all of those things that hopefully you walk away with a clear understanding of how to implement HIT into your workout regimen. That's perfect. HIT stands for HIT stands for high intensity interval training. And that word intensity is the key word. And that's what I really want to make sure people understand the intensity aspect of HIT and why we want to go to a near maximal cardiovascular effort. So that word cardiovascular effort is key. So near mascular, mascular, sorry, near maximal cardiovascular effort with intentional recovery periods that allow you to repeat that maximal effort again and again. So if it's not feeling like a true max effort, it probably is not hit. So what HIT is not is um 20 seconds on, 10 seconds off, minimal rest circuits. It's not lightweights, it's not push-ups, it's not biceps, it's not constant fatigue without enough recovery. So if your recovery is too short, your power is going to drop and you're not going to be able to put out that near maximal effort that hit requires. And you're probably really just doing aerobic conditioning or sub-maximal effort. And the reason you think it's hit is because that is very tiring. It's very tiring to do 20-second work, 10 second rest, 20-second work, 10 second rest. So you think you're doing hit because you feel fatigued. But true hit is being able to go to a near maximal effort with enough recovery so that I can do it again. So I can go to maximal effort again. It is physiologically impossible to go back to maximal effort with only 10 to 15 second rest. And that's where you usually see people's HIT programming with it's very often 20, 10, or 30 seconds, 15 second rest. You're not going to be able to double effort with those short of a recovery period. So what does it look like? I like to use the example of um track athletes for a lot of reasons. So when you see a 100-meter sprint track athlete, they're set up on those blocks, think of how explosively they lead out of those blocks. And then think about their facial expressions, how fast their arms and their legs are moving, how much effort they are pushing to be like one millisecond faster than the runner next to them. And then I also use them as an example because look at their physique. Look how much muscle they have on them. Look how lean they are, how little body fat they have on them. So this is what people want from HIT. They want that metabolism change, they want that muscle mass, they want the low body fat. So they're they're attempting to do HIT because they want those things. They want that power, that speed. But the problem is our programming in our gyms is not really true HIT. Sorry, that was very long-winded.

SPEAKER_00 7:41

No, no, no need to ever say you're sorry, because that was excellent. And I and I'm thinking it through because I feel like when I used to talk about and share with my students about interval training, using that as a um combination, like adding it into your workout routine so that there's that variety and so that you're getting challenged with that kind of a workout. So you're mixing it in with your other workouts. I feel like years ago, we didn't really, or I didn't really know about or referred to HIT training. It was more just interval training. So do you feel, or maybe I missed something along the way, but I feel like the actual HIIT training has become more of a thing in like the last maybe 10 years or so. So it's more of that, again, that high intensity. Whereas I think back then I was just talking about interval training, not so much the high intensity. Is that do you feel like there's that difference a little bit?

Interval Training Versus True HIIT

SPEAKER_01 8:34

Yeah, I agree. I I do think that what most people are doing should be called interval training. Interval training is a great way to push your comfort zone up to a higher level, um, to elevate your fitness. It's a it's got a great place in fitness. And those workouts that are 30-second work, 15-second rests, you know, are great. But to call them HIT is probably a misuse of the term. So interval training has its place, it's great. It's also a way for people who aren't able to yet go to maximal intensities to build up their level of fitness to be able to do those maximal intensities. Um, but I think that HIT as a term has begun to become so popular because people know and they have heard the research that you're going to lose more body fat if you do HIT training. And that is a true thing. If you do HIT appropriately, your resting metabolism after the workout can remain elevated up to 24 hours after the workout. So you are training, changing your metabolism if you do HIT training. That's why I think people like to call it HIT because they're going to put it in their programming and say you're going to lose more body fat doing this training when maybe they're not implementing it in the correct way.

SPEAKER_00 9:48

I love that clarification because that makes so much sense to me. And I hope I would say so for the listeners as well, because I think it is important. I think that's the key reason why we're having this conversation, too, is to bring that clarity to those of those of those, those of you out there, those of you out there who are doing this kind of a workout, understanding that interval training is great. But if you really want to take it to the next level, HIT training is really what you want to strive for.

SPEAKER_01 10:18

And why you want to do HIT training versus interval training? Like I said, interval training is a great way to elevate your gout, elevate some fitness measures. But HIT, you want to do HIT specifically for a few reasons because you are going to be working at an A that recruits your fast twitch muscle fibers. You have slow twitch that are endurance fibers, you have fast twitch that are your fast twitch fibers. That's a very simplistic explanation. But I cannot recruit my fast twitch muscle fibers unless I'm going to a certain intensity threshold. If I'm just doing kind of like, you know, moderate intensity intervals, I'm probably not recruiting my fast twitch fibers. So those track athletes, the way they look is because they are recruiting their fast switch fibers. Those are the fibers that hypertrophy or really improve your muscle definition. So you want to engage in HIT to recruit those fast switch fibers, to reach those maximal intensities that you are at a threat threshold where they'll be recruited. That's one reason to do it. Um, another reason is to train at these high-intensity workloads so that everything else in your life just feels so much easier. If I have this capacity to go to these max intensities, then my daily life or fun adventures or other obstacles in life are gonna feel a lot easier. And I would like to maintain that capability until I'm 100. So if we want to maintain power, we want to maintain speed, we want to maintain the ability to move quick or react. If I'm falling, um, I want to make sure I'm training that power threshold. And another reason is because yes, it does help you burn more body fat. So I wanted to kind of like do the science behind what that is, and because maybe people talk about HIT and the afterburn, or they've heard the term epoch, why you might want to do HIT. How we measure metabolism is based off of how much oxygen you're consuming. So a resting metabolism, like we're just sitting here at rest doing minimal um demand on our body. We would be measuring our VO2 or our oxygen consumption at probably about 3.5 milliliters per kilogram per minute of oxygen consumption. That's a resting metabolic rate. So if I engage in HIT training, I go to these peak intensities, train my body. At the end of that workout, I have to reset my body. I have to um reduce my core temperature, bring oxygen back to my muscles, I have to um clear out lactic acid. There's a lot of things like hormones that all have to be reset after exercise. So while I am just sitting now in my car driving home from that workout, my metabolism is going to stay elevated. And I can actually impact how long that lasts and what the magnitude of that is. So if I go to HIT class and I truly sprint and truly give my full max effort, that epoch or that afterburn or that elevated resting metabolism is going to be a larger magnitude and last for a longer period of time. So that peak intensity will determine how much body fat I can lose from HIIT training. The problem is that going to that heat hit high intensity max effort is really hard for people. The heart rate is really high, you're sweating, you're breathing heavy, all those things feel very hard. So I would still venture to say that even in our HIIT programming, where we do do the appropriate work to rest ratios, which we'll talk about that, I would say my people are not always hitting their max effort because it's really hard to pull that out of somebody. You have to have a lot of motivation and a lot of guns. That's why we're not all 100-meter track athletes.

SPEAKER_00 14:05

So true. And I think it's such a great point that we have to sometimes think we're working at our max, but we might not truly be there. And in order to get some of these results, they don't they don't come easy, right? You have to you have to put forth some effort. And I think it's also important, I know you're going to talk about the ratio. How often do you recommend someone doing an actual HIT workout?

How Often To Do HIIT

SPEAKER_01 14:35

Well, since it is very taxing on your body, um, it is a lot of stress on your muscles, on your cardiovascular system. That stress needs to be rebuilt and repaired. So we and our gym at FitFix, we only put HIT on the schedule on Sunday and on Wednesday. Those are the only two days a week that you can get a HIT class at Fitfix. So I would say one to two days per week is max because I really want you in those two workouts, I really want you to go to your max effort. So if you truly do that, you really need time to adapt and rebuild and repair, recover, replenish, hydrate with electrolytes, um, give yourself carbohydrates and protein, yes, carbohydrates, especially after a HIT workout, and to not stress and overtax your physiological system too intensely too many days of the week. But, you know, like we talked about, some people are doing HIT five days a week. They're probably still not doing their max intensities, but it still can be like you think you're doing, like you said, you think you're doing your max intensity. You are stressing your system. So I would still say one to two times a week and give yourself intentional recovery with nutrition, with sleep, with hydration.

SPEAKER_00 15:58

I think that's so key. And I really hope the listeners are really taking that in and and and and taking it into heart because, you know, as most people in society, they want results and they want like to do as much as they can to get those results. And so I think that we've kind of caught got caught up in the more is better kind of mindset when that's not the case, especially when it comes to, you know, later on in life and our workouts and what we're doing for our overall health and longevity. More is not going to always be better. And especially in this case, I think it's so important that you're pointing out that wanted to workouts, hit workouts a week. And I think it's perfect and it's a perfect testament because that's what you have on your schedule for your studio. And I think that that speaks volumes to have someone like yourself who's educated and knows and says, No, two times a week is plenty. And again, to what you're saying, you know, you have to have that time to have your body recover and rest and rebuild so that you are maintaining and gaining that strength to go back at it harder and just as much as you can for that maximum effort as you did the prior workout. So it's so, so key what you're sharing.

SPEAKER_01 17:16

So, a couple of things about that too. Um, you if you do only do it one to two times a week, you have time in your schedule to balance out your, you know, long, slow aerobic training, your heavy weight training, your flexibility. So you can do HIT every day and also do heavy strength training and get your walks outdoors in. So it also leaves time in the schedule to do all those things too. Um, I lost my train of thought of what I was gonna say for the other thing.

SPEAKER_00 17:42

Well, the variety, because oh, on recovery.

SPEAKER_01 17:45

The variety is key.

SPEAKER_00 17:46

So that's really great what you're sharing.

SPEAKER_01 17:48

But going, sorry, go ahead. Yeah, that is that is something about I was gonna say about the recovery aspect too. Um, on recovery, when how do you know when you're recovered? This is kind of off the topic, but just so people can kind of know, a really good way to assess if you are recovered or if you are overtraining is your resting heart rate when you wake up in the morning. So if you get a baseline measurement, you haven't worked out the day before, you got a good night's sleep, you don't have a lot of stress in your life, you haven't just had caffeine, when you're laying in bed in the morning, don't get up yet. Take a full one minute count of your resting heart rate. Let's say it's 60. Um, that's on a like, you know, a day that you haven't exercised heavily before and all that. So I took get my baseline. Now I should measure that every morning before I wake. And we all have Apple watches now, so you can probably see your resting heart rate when you wake up if you're wearing it, or put it on when you wake up. So before you rise, if I'm going to the gym, let's say, and my resting heart rate, my baseline is 60, and I wake up in the morning, my resting heart rate is 80 B because I didn't get enough sleep, I didn't hydrate well enough, I didn't fuel up well enough, or I've just been hitting the gym back to back to back to back hit workouts every single day. So as we talk about recovery, we probably should know how do I know when I'm ready to do another hard workout? So tracking your waking resting heart rate every day and logging it is a really good way to see if I'm my resting heart rate is higher. I probably should tell myself, I'm gonna do a lower intensity workout today. Today is the day I'm gonna go to the dance class at the gym or the functional flow class at the gym or yoga or something that's a little more restorative for the body.

Work To Rest Ratios That Work

SPEAKER_00 19:32

That's excellent. Thank you for sharing that because I think that's that's that's really important information too for people to know how to track and how to like see if their body is recovering to its fullest. So that's really, really important. What about the ratio, Heather? Like we've we've talked about this before, and you when you were talking about the you know, the 3010 or the 2010, what would you say is ideal or necessary when it comes to an actual perfect ratio for HIT training?

SPEAKER_01 20:07

The answer depends on the length of your work interval and the intensity that you are at. So the harder you're going, that should be the shorter intervals. So anything under two minutes would be appropriate for a hit interval. So you could do a 90-second hit interval, but my intensity is not going to be as high as a 10-second interval. That's where like some people are never doing 10 seconds. We have a hundred meter sprint, it takes 10 seconds or less. So most HIT programs are doing 30-second work, 15 second rest. It's always 30 seconds work, 15 seconds rest. Change it up. Pick something from 10 seconds up to two minutes and work within those different ranges. But just understand that the longer my interval it is, I won't be able to hit full max intensity. So on that case, it would be okay to do a shorter recovery. When I'm all the way down at my 10 second true maximal effort, that's when I need a longer recovery. So some ratios you can work with would be one is the work, two is the recovery. So a one to two ratio is best for a little bit lower intensities, maybe your longer duration of the work intervals. So one to two. So let's say I did 40 second work, that would mean I need 80 second rest, a minute 20. Or been to a hit class at any gym that's like, okay, we're gonna have a minute 20 rest. No. Well, I shouldn't say ever, never, but most likely not. So then the harder you're going or the shorter your um work interval, maybe now you're going up to one to four times the rest interval. So 30 second work, two minute rest for that. Then when you're at those peak 20 second, 15 seconds, 10 second, all out sprint efforts. You need eight times the rest ratio. So if you were doing, let's say this is make the math easy. If you're doing eight 30-second pull out sprint, you should have a four-minute recovery. 30 try it. One day I want to put everybody to the challenge. Try 30 seconds, full out maximal. I cannot breathe after that 30-second sprint. Take a four-minute recovery and then try that maximal sprint again. And if you have something to measure, a treadmill with a mile per hour speed, or you know, your time for a certain distance, see if you can go back and repeat that same effort again. And then maybe you try it with 3015 and see what happens so you can compare. I love that. If you want, if you want true intensity, you have to plan the recovery. You have to earn back the intensity with your recovery. So I can go back and repeat it again. That's what hit is supposed to be. Remember what the definition of HIT is it is high intensity, maximal intensity with recovery to be able to repeat it again. If I cannot repeat it again, then I'm probably not doing HIT.

SPEAKER_00 23:07

And that's just so excellent. I just again I think that clarification is so needed and necessary. I think that there's probably many people out there that don't do not realize that fact. And it makes so much sense. I mean, you have to have your body be able to recover. You have to give it time to recover so that it you can go max effort again.

Recovery Heart Rate And Longevity

SPEAKER_01 23:29

When you're training these high intensity intervals, you are using ATP and you need to replenish that ATP. That's your energy currency when we are doing those high intensity efforts. So if I don't give it time to replenish ATP, then I'm not going to have the power to be able to do it again. Related to the work-to-rest ratios, what you are trying to train also during HIT is your recovery heart rate. So if I can spike my heart rate up to that maximal heart rate, and my body has the ability to drop it down quickly back to my recovery heart rate. So there can be athletes that maybe don't need as long to recover because their recovery heart rate is faster. You have trained your heart rate to come down. And this is really important for longevity. And I think this is this is something that people aren't talking about related to longevity, is my recovery heart rate is correlated to how long I will live. If my heart rate can go up and my heart rate can go down fast, rapidly, that is what fitness is. That's fitness. That is a measure of my physiology has changed. My heart is stronger, my uh blood flow is better. So many things. When you're in your HIT training, week after week, you should start to notice that my heart rate is coming down faster. And you should celebrate that because that means you're gonna live longer.

SPEAKER_00 24:54

I love it. That is something to celebrate. I remember sharing that with my students all the time about the fact that as you become more fit, you're going to reach your resting heart rate quicker. And thank you for pointing that out because, again, that's a really important point for the longevity for all of us to understand that. And that just kind of again brings it back to the basics and back to home, the importance of that regular movement, that regular exercise, that regular getting that heart rate up, shrinking that heart, doing that cardiovascular work and that HIT training, all of that to help us be as fit as we can so that we can live to be 100, right?

Cortisol Fear And Stress Resilience

SPEAKER_01 25:38

Yes, yes. I'm doing 100 burpees on my 100th birthday. I did want to talk about something else because there is a lot of fear around hits and a lot of misinformation about cortisol and hits. Um, we did do a stress and cortisol podcast before, too, that people can listen to. Um, but I wanted to make sure that I help people understand that HIT is not going to negatively affect your cortisol and your stress. There's a couple of really important facts about this. If I don't train my body to handle stress, I am limiting my ability to handle stress. When stress comes in my life, if I'm not able to physiologically handle it, then stress will come at me and I will fall apart. So HIT is a stress, a stressor that builds your resilience, your capability of handling stress. And part of that is related to cortisol. So when any exercise, whether you're walking, weight training, it all increases your cortisol. And it's just like the heart rate response. Heart rate spikes, my heart rate comes down faster. I train my recovery heart rate, my resting heart rate is lower at baseline. The same thing with HIT. If I spike my cortisol, if I spike my cortisol with HIT training, my body is going to become better at managing cortisol. And my baseline levels of cortisol will be lower. This is where the talk out there is not spreading the right message about cortisol. It is good to stress your body, to stimulate your body to adapt, to handle that stress. So your boss get better at managing cortisol if you do HIIT training. It is not the opposite of what everyone else is saying. Don't do HIIT because it's going to raise your cortisol. These are not people that are giving the right message about it. Do it so that you create this armor of stress on your body that all that stress is just going to bounce right off of you. And my baseline levels of cortisol will be lowered, just like my blood pressure is lower with exercise, my heart rate is lower with exercise. Cortisol is the same.

SPEAKER_00 27:57

So excellent. Thank you for sharing that. Because again, you know, it that's the main purpose here. Again, is giving the accurate information, dispelling any myths that are out there. And I mean, you and I have talked about this. We know there's a lot of information out there, and it's not all accurate. So that's the whole point of this. And for all of our listeners, you know, bringing someone on like Heather who can really give us clarification and give us the facts that are based on science and exercise physiology because that's what we want to follow. So I thank you so much for doing this and taking the time to share this information. It's so, so valuable.

SPEAKER_01 28:38

Thank you. I hope it was helpful. I hope people can pull out some nuggets and apply it to their own training and try a new way of doing hit. See what happens when you really hit those maximal intensities. You recover intentionally so that you can repeat it again and then see if you don't see muscle mass increasing, if you don't see body fat decreasing, and you don't see your just your stress armor building. Try it and maybe everybody can message you back and let you know let you know.

Try It And Share Results

SPEAKER_00 29:10

Yeah, definitely. Those of you who give this a try, definitely let let us know. You know, maybe take some videos or some pictures and share and tag Heather myself. And would love to know those of you who start to apply this. And maybe you think you've been doing the HIT training, but with what you've learned today from Heather, um, give it a try and and take it to that next level. And yes, we would both love to hear about what you are doing. So tag us, message us, and let us know your progress. And as always, everyone, take time for your wellness on this day. Take some time and get out there and do some HIT training. And thank you, Heather, so much. So appreciate you. Thank you. We will do this again and have a beautiful, blessed rest of your week, everyone, and we'll see you next time on Words of Wellness. Thank you so much for tuning in to today's episode. I hope you gained value and enjoyed our time together as much as I did. And if you know someone who could benefit from today's episode, I would love and appreciate it if you could share with a friend or rate and review Words of Wellness so that more can hear this message. I love and appreciate you all. Thank you for listening. And if you have any questions or topics you would like me to share in future episodes, please don't hesitate to reach out to me through my contact information that is shared in the show notes below. Again, thank you for tuning in to Words of Wellness. My name is Shelley Jeffries, and I encourage you to do something for you, for your wellness on this day. Until next time, I hope you all have a healthy, happy, and blessed week.