14 min read

Interval Training (Part 1)

Interval Training (Part 1)
Photo by Alex Lerum / Unsplash

Interval Training was the buzzword for the last few years.

I’m happy to say that the buzz and foreign association people used to have with it is gone, and it’s become a staple in the fitness world.


Because it works!

Want to learn all the stuff you won’t find on Wikipedia?…

Before I begin, some people will refer to interval training now as ‘High-Intensity Interval Training‘ or HIIT, so if you see me use that acronym, you know what it means.

Part 2 and Part 3 will be a brief overview of all the ‘types of interval training you are bound to find on Google and a slew of protocols you can actually try.

What is Interval Training?

Simply put, interval training or HIIT is a type of training where you do a period of higher intensity work — generally a higher intensity than you could tolerate for more than a few minutes at a time, but not exclusively if you consider aerobic intervals — and pair it with a period of rest or lower intensity work.

The amount of work to rest can and will vary depending on the desired training outcome, and the measurement of the work to rest can change too.

For example the Work:Rest can be even, like 30 seconds on: 30 seconds off, or it could be staggered for different training outcomes like 15 seconds on: 45 seconds off, or it could be a distance; 100m on: 300 m off.

You’ll also see me use 3:1 or 1:6 in describing different protocols below, which always means work to rest ratio (work:rest), but you’ll always see me record the unit of measure.

For a quick look at a few different interval protocols used to train the three major energy systems, please see this article.

Why Interval Train?

Recently at a fitness conference, I witnessed a noteworthy and reliable cardiac rehabilitation specialist give a presentation on the interval training they were using in their cardiac clinic to help people recovery from conditions like heart attacks, peripheral artery disease, angina, stroke, etc…

Now if you know anything about cardiac rehab, you know this is generally considered a faux pas.

By far the most common exercise recommendation for cardiac rehab patients is long slow aerobic training (monitored).

Unfortunately, this is the norm and there is, in general, a strong fear about eliciting higher intensity training on an already stressed cardiovascular system, even though I’ve never personally read any unequivocal proof that higher intensity interval training increases the incidence of cardiovascular problems, or that they should be considered dangerous in any way.

It remains a popular assumption, even in the medical community, that high intensity is bad.

I disagree, somewhat.

Pushing out the duration/distance increases the aerobic quality, but most people in this situation have a hard time expressing relatively low levels of exertion for longer than 60-90 seconds anyway.

From a practical standpoint, if you’ve ever seen or worked with someone recovering from a cardiac issue, it looks exactly like interval training already because they can only tolerate a certain amount of work for so long anyway before they simply must rest and recover.

What do most fitness professionals already recommend for people who want to start running?

Walk-Run protocols.

What are walk-run protocols?

Interval protocols…

…Getting back to this particular researcher and cardiac rehab specialist, he confirmed my thoughts…

He asserted that the fear of using interval training in cardiac rehab settings isn’t supported in any of the research he’s seen either, actually, I think he summed it up best:

For most of these people, all they can do is a form of interval training anyway.

From a practical point of view, most of our lives are already spent in a constant state of interval training, and it makes a great deal more sense that when trying to get fit, interval training is probably the way to go as a general rule.

If for no other reason than to keep the quality of your work output high, and allow rest when you need it.

People learn techniques significantly better if they can keep themselves feeling reasonably fresh. That’s why it is far easier to learn how to run well, using an interval protocol; Before you try to run for an hour for the supposed weight loss or health benefits.

There needs to be a gradient improvement in ability over time before distance work can optimally be achieved.

Rest keeps a higher quality output going for longer, making interval training overall, probably safer, less taxing and more effective.

Is It As Effective For the Heart?

Interval training can be quite effective depending on the protocol. A great deal of research shows that it increases V02max significantly more than steady-state work, but the jury on the heart specifically is still out.

There is evidence to suggest that some intervals (namely HIIT varieties) don’t maximally fill up the left ventricle of the heart because the heart rate increases greatly.

This seems more like a misunderstanding about what interval training is as compared with HIIT.

Hint: Intervals don’t and shouldn’t always mean maximum heart rates…HIIT does…

When the heart rate increases, the stroke volume by association may decrease, or the amount of blood that fills the chamber of the heart between each beat. High-intensity interval training might therefore be inferior for actual heart health as compared to the aerobic interval.

Currently, it’s theorized that too much high-intensity work isn’t leading to much elasticity improvement in the left ventricle of the heart. As would commonly be seen when training the heart in the more aerobic 130-150 beat per minute (BPM) range.

However, this range is easily achieved with low-level activities like hiking, walking, yoga, swimming, pilates, mobility training sessions and a variety of low-intensity exercise options. You can also, of course, do interval training in the aerobic zone to fulfil that need too.

On the other side of the coin, recent trends have fitness professionals advocating that intervals should only be high intensity. A big mistake in my mind.

This discounts the relative importance of challenging the heart at a variety of intensities and not just at high intensities. If you redline a car endlessly, you’re sure to damage the engine.

“You’re not awesome because you go hard all time. You’re awesome because you know when to push yourself and when to pull back.”

Click to tweet

Because of the confusion, it’s created, I’m not a fan of how quickly the abbreviation HIIT has suddenly been applied to any form of circuit training or interval based training. They are not the same thing.

HIIT requires maximum intensities and is different from mere interval training. Most beginners will not be able to reach their maximum intensity that often, if at all. Thus, it’s not a great starting point even if it is time-efficient. Interval training at lower intensities is a better option as a starting point.

Interval training just means a period of work and a period of rest, repeated; That should include a spectrum of high, medium and lower intensity physical workloads I’ve discussed in previous articles.

i.e. taxing the 3 main energy systems as a whole, rather than one or two and hoping for a trickle-down effect.

There appears to be a greater carry-over from anaerobic energy system work to aerobic improvement, than vice versa, but we cannot solely use this as a recommendation for high intensity all the time.

The aerobic energy system is very involved in the recovery aspect of anaerobic training, particularly after repeated bouts. That even applies to the rest you take between resistance training sets.

i.e. The aerobic energy system is very involved by the 10th rep of a high intensity repeated bout of interval work, but not so much maybe during the first or second bout where recovery is not completely required. This is why most interval protocols need more than 1-3 intervals to get the trickle-down benefits.

This is a good reason to make sure you train more aerobically with longer interval protocols like 2 minutes on, 1 minutes light on occasion. Maybe even allow for longer breaks between all-out efforts–like a 30 second Wingate sprint, which features a 4 minute recovery period after the all-out effort.

I know long rests seem counterproductive to the high-intensity thrill-seekers, but rest is important and how hard something feels or the sweat you produce doesn’t dictate the effectiveness of a training program – results do.

The problem with high-intensity work is that you can’t do a ton of it in the week and you can’t do a ton of volume. That’s where aerobic training can slip in and do its thing one to six times a week even.

You get aerobic heart rate work by letting the heart rate drop during recovery back into that 120/130-150 BPM range and long rests reduce volume.

What really should be noted is that there are a variety of ways to tap the aerobic system that aren’t low-intensity-steady-state (LISS) work (AKA long-slow-distance cardio), so long as a moderate heart rate can more frequently be maintained. I discuss a bunch of these methods with clients in Fitnack.

The objective of intervals isn’t always to keep your heart rate as maximally high for as high as you can, as some people may assume. That’s HIIT. Are we clear?

Interval training can and should easily meet the demands of all three energy systems by using a variety of volumes and intensities.

Remember Work + Rest = Success

*Note: If you’re at roughly a 60 BPM heart rate upon waking, you probably don’t need as much in the way of aerobic conditioning overall, but you may as well continue doing a little light intensity work a couple of times a week. Moving and being active is a great way to recover from higher-intensity forms of exercise.

Non per soli uomini
CC Marco Crupi

Quick History and the Science

Interval training’s rise to popularity got its start with a Laval Study published in 1994.

The often misquoted study was heralded as ‘yielding 9x‘ the amount of fat loss when compared to steady-state cardiovascular exercise or ‘long-slow-distance’ cardiovascular exercise that required twice as much work. AKA MICT = Moderate Intensity Continuous Training.

This is not entirely true, the results actually revealed 3x the results with half as much work.

The reason it got inflated had more to do with a fudged mathematical formula applied to the difference in duration of exercise and the changes in body composition as measured by anthropometry.

The study is often criticized because less than a kg of total weight loss was present after 15 weeks of training. Can you imagine working your butt off for 15 weeks and not even showing a 2-pound drop in your weight? Tough…

However, you couldn’t deny that it still worked better than steady-state work relative to the time invested, and it sparked enough interest to open the floodgates of research.

One might also assume given other research, that fat loss would be dependent on the starting point of the participants and would have been much better overall had this exercise intervention accompanied a nutritional intervention. We generally know that exercise on its own doesn’t do a great job at helping people lose weight, but when you combine it with nutrition, now we’re talking.

Since then the famous Tabata Study, published in 1996, and a follow-up, published in 1997, showed us that we could significantly improve anaerobic and aerobic fitness, with a mere 4 minutes of training per session — well and another 70 minutes of aerobic training per week but nobody talks about that…

Whereas the long slow steady-state cardio comparison, only improved aerobic fitness and not by much over this much faster protocol.

Now contrary to what many people believe, this study — and actually most interval training studies completed — was only applied to markers of energy system development, and not weight loss or fat loss. Many others have looked at cardiometabolic risk factors (i.e. health factors like blood lipids) but very few have actually looked specifically at fat loss.

More recently, the work of Dr. Steven Boutcher, in Australia, did start to look at fat loss.

His research has given an implication that 8 seconds on, 12 seconds off, might be the best protocol for fat loss. If only compared to the 3 other protocols he used, over the short amount of time he experimented with them, so more research is obviously needed.

I would argue that there could never be a ‘best’ protocol, in that the body eventually adapts to whatever you throw at it, and you would have to mix the protocol up eventually to continue to make progress.

As I’ve indicated before in my work, this seems to occur generally anywhere between 3-12 weeks depending on ability or experience. Also boredom in the real world.

Even in regards to the initial Laval study, I would be willing to bet, had they not done the same thing for 15 weeks, there would have been better results across the board, though difficult to actually research a singular variable in this way.

That being said, it seems that interval training can lead to positive hormonal changes, fat oxidation (post-workout) and improvements in both aerobic and anaerobic fitness with shorter time commitments than long-slow distance work. Huge plus.

It also seems to preserve muscle mass and manipulate metabolism in a positive light, which means better results in less time overall.

The problem with research is the need to isolate variables, though isolation of variables (like trying to isolate a muscle) is nearly impossible to do, research can still at least shed some light on what I think we should already know.

The leanest athletes on the planet are seemingly involved in intermittent power sports, not long-slow endurance sports. Presumably, this happens because the start-stop nature of their energy system work helps maintain muscle mass better. However, intermittent power sport athletes are also far more likely to participate in the big daddy of muscle preservation: Resistance Training.

Aerobic training isn’t muscle wasting, as I often read online. That’s a crock. It’s that endurance athletes often do too much of it and don’t do much strength training. Strength or resistance training is really the difference-maker when it comes to muscle retention/growth — though also total calorie intake and protein intake.

Research suggests that 1-3x a week of non-weight bearing aerobic activity for 20-30 minutes has minimal if any effect on muscle mass retention or growth — so long as the excess caloric burn is accounted for. That may be the other difficulty for endurance athletes, merely eating enough to support muscle mass. Muscle mass isn’t as desirable for performance in endurance sports as it is in power sports.

Maintaining the aerobic pathways also helps people lose fat (and maintain heart health) in specific instances. For instance, even if you’re trying to gain muscle mass, many people will want to lose some of the fat that came along for the ride. Bulking and cutting it’s called, though not that applicable to most people who read this blog. Maintaining some aerobic work even while bulking (gaining muscle) can help trainees cut later (by maintaining fat oxidation pathways via aerobic training).

Getting Started

What you are about to read in Part 2, is a huge overview of a lot of different types of intervals, there are more than you know, believe me, it took me a while to write this, just because I kept thinking of other ways I’ve utilized interval training protocols over the years. Not all of them will be strictly intervals but variations on that theme.

Just when I thought I was finished…

…There was more…

I’ve tried to categorize things as best I can, but sometimes the terminology differs from coach to coach, circle to circle.

Before you begin, I do have a set of criteria you should meet before attempting interval training.

If you’ve never done it before, or have and possibly ended up injured — injury with interval training is typically a result of too much too soon, a mobility issue, a strength issue, or generally a lack of ideal homeostasis, all of which can typically be addressed with other sound training principles — doing it, then you probably want to ease into it gradually.

Many people ask about the safety of Interval Training.

Isn’t it more strenuous on the body?

Shouldn’t you have a strong aerobic base first?

As it turned out above, probably not…

Though I generally don’t recommend doing more than 30 minutes worth of it at any given time, and very rarely more than three times per week.

You’d be wise to start on some kind of non-weight bearing modality too, like a stationary bike, a rower or even *cringe* an elliptical machine.

That being said I played basketball and volleyball for years (both Interval-esque sports), and many of our practices, training sessions and games, would be 1-3 hours long of a start-stop form of practice for 4-6 days a week. I was a lot younger then too, so the older you are, the more caution you should use.

With good nutrition, a lot of sleep, appropriate progression leading into it (starting small and working up to greater volume) and an appropriate amount of variance in intensity, you could probably do more, but I just rarely see the need from a typically ‘gym’ viewpoint.

Often the point, as you’ll see, of interval training is to spend less time in the gym, not more, while getting better or equal results.

I used to recommend that everybody work up to at least 20 minutes worth of long slow aerobic work at a rate of perceived exertion of about 6 or 7 out of 10 — 10 being the hardest you feel you could possibly work.

Ironically enough though, this usually meant starting with running for 1 minute, and walking for one minute, then adding a minute to the run every time you felt capable until you could run for 20 minutes, which if you haven’t already guessed it by now, is an Interval Protocol!

Basically, I was always recommending intervals to build an aerobic base anyway, but if you want to be extra cautious then you could continue to follow that principle, but I’ve since switched my point of view.

What do I recommend now?

It depends on the type of exercise you're doing (running vs cycling vs rowing vs elliptical vs cross country vs etc...).

But a good time-based starting protocol is to err on the side of conservative:

  • 10 seconds on, 50 seconds off (typically a 10-second sprint or faster push, followed by 50 seconds of walking)
  • Or 15 seconds on, 45 seconds off.
  • I've also been using the McMaster Protocol a lot as a starting point (with everything that isn't running) too, which is 20 seconds on, 2 minutes of recovery.

I don’t necessarily mean sprint as in running, just a sprint as in a short duration at a higher intensity of work than slogging it out. Only run or jump if you’re confident with it as a starting point, otherwise, start with something non-weight bearing as previously mentioned.

Now there may be technical issues in someone’s ability to run, but I actually find it easier to teach people how to sprint, than to run at sub-maximal speeds. Also, I’d start on soft surfaces like grass if possible. Interval training like this allows a lot of time for coaching while you catch your breath. A walk-run protocol (another interval protocol) is probably a good way to go for learning to run as a result.

Rest permits again, high-quality work output consistently. Less fatigue = better movement patterns. Speed is very coordinated and neurologically intensive beyond what pure aerobic (steady-state) work would require. This is what makes HIIT so effective and time efficient.

Try it for 5 minutes even, then gradually work up to 20-30 minutes total. Rarely do I recommend people take intervals beyond that time frame unless they’re done in an aerobic range (4 minutes on, 1 minute off as an example).

Continue to (weekly or monthly) increase the amount of work, and decrease the amount of rest, until you can work at a 1:1 ratio, and then I often progress people into aerobic intervals like 2:1, then 3:1, then 4:1.

Following a good progression of that (now 2 phases of training) we can now switch things up and consider moving into higher intensity variations. Many of which are discussed in the next 2 parts.

Remember to should switch things up roughly every month or two. This may mean you have to change the type of interval protocol you’re working on as I note above, or the energy system you’re trying to develop, and in many cases a hybrid of both of those changes.

You also want to start with lower volumes/intensities and progress those over the month or two you practice any given interval protocol.

For instance, week one of the aerobic interval protocol is 2:1 ratio, then 3:1 ratio in week 2, 4:1 in week 3, and 5:1 in week 4. I slowly increased the volume by decreasing the rest over a 4 week period. This is a safer way to go about programming this type of thing on your own and ensures you won’t crush yourself right out of the gates.

Look out for Part 2, which is a juggernaut of a resource…

See this article again for more info on energy system development.