Pete RohlederHigh-intensity interval training, or HIIT, is many people’s favorite time-efficient means of conditioning. The bouts of intense exercise followed by short rest rounds are undoubtedly challenging and effective, but is what you are doing actually high-intensity interval training, or is it something else?
Let’s find out!
Today I will discuss four modes of interval training to ensure you are training optimally for your goals.
A Visual
So a little about me and my taste in fashion- I love hats. I’m not fashion adventurous, so I stick to beanies and baseball caps and wear them all the time. Let’s focus on baseball caps.
Just go with me for a second.
Sometimes I wear it backward, and sometimes I wear it bill forward. Sure, they’re fashionable, but they also can serve a purpose. I’m not judging, but I want to facepalm when I see someone with their hat on backward in the blazing, bright summer sun squinting and using their hand to shield their eyes to see.
I get a giggle from it, and I say to myself, “you do you,” but I can’t help but feel like things would be so much easier for the person if they just used the hat as it was intended.
That’s how I generally see high-intensity interval training in today’s industry.
Often, I see it as a “fashion over function” way of training, meaning that it’s more about the glitz of the challenging exercises and cool acronym HIIT than the actual purpose behind the training.
A Quick Check
Now before I go any further, let me say I love high-intensity interval training. Its efficacy is evident in the mounds of research and literature and has been utilized in performance settings for years.
But I actually don’t perform high-intensity interval training, and I would guess that most of you probably don’t, either. At least not by the definition and standard of what traditional High-Intensity Interval Training is.
Look, I recognize that what we really mean by HIIT is that we are doing tough training intervals. And that’s great! And if it’s helping you achieve your goals, keep at it.
But I want to differentiate this because training the right way matters when training for a specific goal.
Anything intense with rest is considered high-intensity interval training in the fitness industry, but that’s not entirely accurate. This leads to a lack of foundational knowledge of the physiological responses occurring and poor training implementation and progression for specific goals or outcomes. This decreases results, can lead to overtraining, and possibly set you up for injury.
I’m talking about this, not to bad-mouth high-intensity interval training or what the industry has labeled it. Call what training you do whatever you want.
If you’ve listened to this podcast, you know I’m all about efficiency and training as optimally as possible. So that means understanding how and why you’re training a certain way to maximize your efforts. It means approaching training in the most appropriate way to avoid the pitfalls I mentioned earlier.
Let’s talk about what HIIT really is and if there are alternative modalities of intense training that may benefit you more specifically for your goals.
Benefits of High-Intensity Interval Training (HIIT)?
HIIT involves repeated bursts of vigorous-intensity exercise, lasting a few seconds up to several minutes and separated by passive rest or low-intensity exercise. Numerous studies have indicated that this approach and other forms of intense interval training are time-efficient alternatives to induce physiological and cardiorespiratory adaptations. Further, studies have shown countless other benefits. Let me list some for you.
- Burns more calories and increases postexercise fat oxidation and energy expenditure more than steady-state exercise, King et al. (2002)
- Decreases total cholesterol and LDL-cholesterol while increasing HDL-cholesterol, O’Donovan et al. (2005)
- Improved body composition, Sultana et al. (2019)
- Significantly reduce subcutaneous fat, especially abdominal fat, Boutcher et al. (2011)
- Improved resting metabolic rate, Schubert et al. (2017)
- Improved substrate metabolism, Whyte et al. (2010)
- Improves insulin sensitivity, Jelleyman et al. (2015)
- Increases free testosterone levels, Dote-Montero et al. (2020)
- Lowers risk of CVD, Cassidy et al. (2017)
- Lowers risk of Breast Cancer, Mijwel et al. (2019)
- Lowers risk of Metabolic Syndrome, Dun et al. (2019)
- Lowers risk of Osteoarthritis, Keogh et al. (2017)
- In patients with CVD, reduced blood pressure, improved endothelial function, lipid profiles, VO2 max, left ventricular and overall myocardial function, Barclay (2012)
- Improvements in endothelial function, VO2 max, body mass index (BMI), body fat percentage, blood pressure, and glucose regulation, Tjonna et al. (2008)
- Improves cognitive flexibility in older adults, Mekari et al. (2020)
- Provides positive effects on cognitive performance and psychological outcomes in youth, Alves et al. (2021)
- Improves mood and decreases feelings of depression and anxiety, Korman et al. (2019)
- Safe for youth and aging, as well as safe for individuals with diabetes, stable angina, heart failure, post-myocardial infarction, postcardiac stenting, and coronary artery grafting, Barclay (2012)
Just a reminder: always consult a physician before jumping into an exercise program if you fall into one of these categories but the benefits seem overwhelming. Of course, there are a couple of possible drawbacks that you should consider.
Potential Drawbacks of High-Intensity Interval Training
First, there’s the risk of injury. Higher intense exercise comes with inherent risk, so keep that in mind before jumping in.
Something else to consider is that this type of training requires high levels of motivation because, let’s be real, it doesn’t feel great when you’re close to max heart rate and your legs burn and are as heavy as concrete.
Additionally, it would be best if you were mentally prepared for difficulty, as interval training is challenging on many levels, psychologically included.
Finally, be aware of the potential for overreaching, overtraining, and burnout. Fatigue accumulates quickly with interval training; if proper recovery modalities are not followed, overreaching or burnout creep up quickly.
What is High-Intensity Interval Training (HIIT)?
Now, let’s define HIIT so we can build from there.
Traditionally, High-Intensity Interval Training has its origins in endurance performance settings. HIIT is designed to improve maximal performance in endurance settings, specifically improving VO2max. HIIT is designed to be “all out” with the goal of training at or above anaerobic threshold while maintaining performance qualities.
That doesn’t mean just completing the session- it’s completing it with a high-level, executed technique and performance.
When we say anaerobic threshold, we mean training at the highest exercise intensity you can sustain continuously without lactate substantially building up in your blood. The longer we can sustain this, the longer and harder we can exercise, leading to improved performance.
The traditional approach to HIIT training is unimodal, meaning one type of training, usually running or cycling, with training thresholds at near maximum effort, ≥85% HRmax. And because of this intensity, the work-to-rest ratios were 1:2 or 1:3, significantly different than what most HIIT programs call for today. And that makes sense if you know what you’re tapping into from a physiological perspective.
To obtain the results we’re after and maintain performance, we need to ensure our training duration, intensity, and recovery elicit the adaptations we want, which means we need to recognize the influence our training has on our energy systems. This is key.
Bioenergetics 101
This means Bioenergetics 101, crash course style.
ATP. Adenosine Triphosphate. It’s the energy our bodies use. If the body were a car, ATP would be the fuel. But unlike a car, we don’t have a tank of it ready to use. We have to produce it. And how we train and how long we train will determine its rate and source of productivity.
So right now, your body is producing it—all the time, as we speak. If you’re at rest, the body has a nice flow, using the oxygen you breathe to produce it. It makes enough for your body to get what it needs to maintain its functions.
But when we start to exercise, a new demand is put on the body, and things get triggered. Multiple pathways are utilized, and all are contributing.
I like to use the visual of a spotlight. Everything else is still happening in the background, but a spotlight focuses on one area. It’s similar to ATP production during exercise. So don’t look at each of these as a light switch: one turns on, and the other turns off. Instead, think of a spotlight emphasizing one over another, based on the intensity and duration of our exercise.
Energy Pathways Through a Narrative
I’m going to describe this through a narrative so you can visualize the process.
You are seated. Right now, your body is producing ATP aerobically. But you decide you want to take off sprinting. So, you do—the demand for ATP skyrockets due to the intensity.
Muscles are forcefully contracting, respiratory rate climbs, and more ATP is needed. Remember that our muscles have enough oxygen, but they switch to alternative forms in times of intense energy needs because they are quicker at producing energy.
Creatine Phosphate System
So, the spotlight switches to our ATP reserves. This is our creative phosphate pathway or alactic pathway.
This will give us about 10 seconds of all-out effort or up to 30 seconds of near-maximal effort before the reserves are depleted.
I had a fantastic Professor in school that gave me the visual of a toilet being flushed. You get one flush; after that, you must let the tank refill.
That’s this system. It takes about 30 seconds to replenish about 70% of the phosphagens and about 3-5 minutes to be 100% replenished.
So, if you wanted to train or utilize this system, you would need to consider the amount of rest between bouts of exercise. You see where I’m going with this.
Glycolytic Pathway
Well, you’re sprinting but don’t want to stop, and you’ve been sprinting for 40 seconds now. ATP needs to be rapidly produced, so the spotlight switches to the glycolytic (or anaerobic) pathway.
Here, glucose (or sugar) is broken down to fuel this process. There are several steps, and with each step, there are ions and byproducts that will be used later for more energy production.
You have pyruvate at the end of glycolysis, and that molecule can go one of two ways. That fork in the road is decided by you.
Fast Glycolytic Pathway
If you keep sprinting at the highest effort, that pyruvate will convert to lactate and hydrogen. This is considered the fast glycolytic pathway.
That lactate will enter the blood, head to the liver, and convert to glucose to be used again.
But it comes at a cost. That hydrogen doesn’t stay out of the way. If you are giving yourself little breaks between the sprints, it is buffered as long as the body can keep up.
But, if the intensity is too high or continues too long, it accumulates. That accumulation of hydrogen ions will impair the muscle’s ability to perform work and increase muscle pain receptor sensitivity.
Also known as “the burn.” This can last up to about 120 seconds before a change is needed.
Slow Glycolytic Pathway
So the burn starts to kick in, and you decide you can’t keep up at that intensity.
The only choice you have is to decrease the intensity. Slow down.
Slowing down and decreasing the intensity switches the spotlight again.
This time, the pyruvate goes the other direction and converts to Acetyl CoA to enter the aerobic pathway. This is still high-to-moderate intensity and can last up to 180 seconds.
Since it’s still using pyruvate, it’s considered the slow glycolytic pathway.
Oxidative Pathway
The sprint you started with has now turned into a run. You want to keep going, but you know that to continue, you have to pace yourself.
Once you go over the 180-second mark, your body will again switch the spotlight to the aerobic (or oxidative) pathway, assuming the intensity is manageable.
Here, all the byproducts from glycolysis and the breakdown of other substrates in the body are used to produce energy. This pathway takes longer to produce energy, but it produces the most compared to the others.
And depending on the type of activity you do, that spotlight will continue to jump around to ensure enough energy is produced.
The Takeaway for High-Intensity Interval Training
So what’s the takeaway here from this crash course?
That shift from anaerobic to aerobic is significant for performance improvement. Depending on what you want, you need to train and improve the correct energy system for your goals.
You’ll want to base your work-to-rest ratios, duration, intensity, and modes of interval training on what you are trying to achieve.
Further, it comes down to recovery. The longer you recover, the more dynamic, explosive, and forceful you can be.
The less rest you have, the more you train the slow glycolytic and aerobic pathways that can improve power-endurance and endurance qualities.
Really, I am saying you must define your goal of interval training so you can program the appropriate mode that is ideal for your desired outcomes.
Modes of Interval Training
So what modes are there? As I said earlier, high-intensity interval training focuses on improving VO2max. So if you are doing a 1:1 work-to-rest ratio, based on what we just talked about, you may need more rest time to sustain the training intensity needed to improve VO2max.
Are there other types of interval training that may align better with goals other than improved aerobic capacity?
Absolutely! Let’s jump into them!
High-Volume Interval Training (HVIT)
The first is the one most people are familiar with but refer to it as high-intensity interval training. Remember, proper HIIT is about improving aerobic capacity while elevating performance, focusing on specific intensities for those adaptations.
What many people are doing is considered High-Volume Interval Training (HVIT).
The goal of HVIT is to increase caloric expenditure through metabolic-demanding exercises, improve cardiovascular function, and improve muscular endurance and strength-endurance, so challenging anaerobic threshold is critical.
This type of training is multi-modal, meaning different types of exercises are used.
An example would be intervals of air squats, followed by mountain climbers, burpees, and bear crawls. This is just one example, but you get the picture.
Further, work-to-rest ratios are 1:1 or even 2:1, so fatigue accumulation is significant.
The focus of this training is reaching near maximal effort, but since work capacity, not performance, is the goal, the intensity will diminish throughout the training session. It’s about completion, not peak performance, which is a much different approach than high-intensity interval training.
Since we are pushing anaerobic threshold, we will see aerobic capacity improvements, but the specificity of training and diminishing intensities will yield various adaptations.
Remember, it’s about your goals.
Variable-Intensity Interval Training (VIIT)
But what if you have goals of improved performance and endurance or strength-endurance?
A more structured approach to your intervals will be needed, which is what Variable-Intensity Interval Training (VIIT) is all about.
The goals are accomplished by combining near-maximal effort intervals (~ ≥85% HRmax ) with pre-programmed sub-maximal intervals (<75% HRmax) interspersed in the session.
This means that work-to-rest ratios will vary; some will be 1:2 or 1:3, similar to HIIT ratios, and some that are 1:1 or 2:1, similar to HVIT ratios.
This allows adequate recovery to perform at a high level but still improves endurance and strength-endurance qualities.
For all interval training modes, paying close attention to heart rate is vital, but to ensure enough recovery for VIIT, really focus on the percentages you want to train at for each of the prescribed ratios.
High-Intensity Functional Training (HIFT)
This last one combines the previous but with a change in goal and approach.
High-Intensity Functional Training (HIFT), also known as High-Intensity Power Training, aims to improve overall fitness and power-endurance through sustained, high-power, multi-joint resistance-based movements.
The focus is on challenging energy systems through constant work and varied training modes, most revolving around strength-training exercises.
For example, it could be box jumps, medicine ball slams, and kettlebell thrusters with varying intensities.
The key to HIFT is to vary your work-to-rest ratios based on your primary focus. If performance is the primary focus for the day, you’ll train at near max heart rates. If power-endurance is the goal, perhaps you utilize a “rest when needed” approach to allow recovery when needed but still push work capacity.
Getting Started with High-Intensity Interval Training or other Modes
So how do we get started with this? And if we are training or coaching clients, how can we introduce this in a way that doesn’t intimidate or overtrain them?
My first recommendation is to start slow because a little goes a long way.
One way to do it is to sneak a short interval round into your or your client’s regular routine to introduce it and gauge how it goes.
Start with longer rest ratios and keep the intense rounds moderate-intensity first. Start easy. Pick one body weight, cardio-based exercise you like, and perform it for 30 seconds, followed by 30 seconds rest, and repeat five times.
There are five minutes knocked out right there.
If that’s easy, add active rest for 30 seconds rest, like holding a plank or a wall squat.
It doesn’t have to be flashy, and it doesn’t have to be complex. It just has to tap into the suitable systems.
Regardless of what mode of interval training you select, one thing is sure: improved health and fitness will occur. The difference comes from what specific adaptations you want; your approach matters if you wish to achieve efficient results.
Recap
To Recap:
High-Intensity Interval Training (HIIT): focused on performance
High-Volume Interval Training (HVIT): focused on caloric expenditure; completion, not performance in the goal
Variable-Intensity Interval Training (VIIT): both aerobic and strength-endurance performance goals, so changing intervals to match is the the goal
High-Intensity Functional Training (HIFT): improve overall fitness and power-endurance through sustained, high-power, multi-joint resistance-based movements, so work-to-rest ratios will vary based on primary goal.
Conclusion
Thanks so much for tuning in. It means the world to me, and I appreciate you.
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I look forward to chatting with you next time!
Take care of yourselves, and remember, wherever you are, keep moving.
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Pete Rohleder
