Back to regular programming (intervals vs. endurance training)


As of September 2017, new Sweat Science columns are being published at Check out my bestselling new book on the science of endurance, ENDURE: Mind, Body, and the Curiously Elastic Limits of Human Performance, published in February 2018 with a foreword by Malcolm Gladwell.

- Alex Hutchinson (@sweatscience)


I’m back home from a fascinating couple of weeks in India — many thanks to the athletes, coaches and scientists who shared their time with me. More articles to come, which I’ll link to in future posts.

img_2158-1In the meantime, the blog will get back to its bread-and-butter: reporting on new research related to exercise, fitness and sports. For starters, a study in the current Medicine & Science in Sports & Exercise adding to the debate on the benefits and shortcomings of short, intense interval training for cardiovascular and other health benefits, from Lars Nybo’s group in Denmark. (The full text is freely available online.)

The study: four groups of nine untrained men did a 12-week training program:

1) Interval group: 5 min jog warm-up;  5 x 2 min HARD (getting HR above 95% of max); 1 min break between intervals (not clear from the paper, but I assume they just rested between intervals); 3 workouts per week, but they only completed an average of 2.0 due to factors such as injury (more on that below).

2) Endurance group: 1 hr of running at 80% max HR; 3 workouts per week, though they only completed 2.5 sessions on average.

3) Strength training: this group did three weights sessions a week. Not that interesting — they managed to confirm the well-known fact that running doesn’t give you bigger muscles, and lifting weights doesn’t improve aerobic fitness. (They probably should have to used these subjects to increase the size of the other groups…)

4) Controls who did nothing.

The key results are that (a) interval training produced double the increase in cardiorespiratory fitness that endurance training did (14% boost in VO2max compared to 7%); and (b) interval training was much less effective at lowering resting HR, body fat and bad cholesterol.

This is all good — we can all agree, I think, that different workouts do different things. Unfortuanately, you can’t cram all the benefits of an hour-long endurance session into 20 minutes. The big pitch for HIT (high-intensity interval training) is that it’s so much more time-efficient than the standard slog-on-the-treadmill-or-bike-or-elliptical workout. This is true. But the revised message of the last couple of years’ research is that you can adjust part of your weekly routine to HIT, not all of it. And in fact, you’re actually better off doing, say, 1-2 HIT sessions and 2-3 longer, slower runs per week than just doing four of the slower sessions. High-intensity has some major benefits beyond simple time-efficiency.

The one point that I wanted to circle back to is the injury question. The subjects in this study apparently hadn’t “participated in any type of regular physical training for at least 2 yr.” I don’t see any reference to a breaking-in period or a gradual ramping-up period — so it’s remarkable to me that ANY of the subjects made it through this study alive! Running for an hour continuously is a pretty tough task for an untrained subject, let alone a hard interval session. As it is, of the nine interval subjects, three missed sessions with shin splints, another got plantar fasciitis, and a fifth had “bilateral unspecific knee pain.” In the endurance group, two subjects had overuse injuries.

To me, that’s a pretty important point. If more than half of the subjects in an experimental group get injured, that’s a relevant detail when you’re talking about public health advice. The subjects in this study presumably had access to experts who could tell them how to deal with their injuries. For the average person outside the lab, encountering shin splints, plantar fasciitis or unidentified knee pain could easily spell the end of their attempt to get in shape.

Don’t get me wrong — I’m a big fan of interval training as a powerful and efficient way of getting in shape. But it’s an approach that does carry some higher risks, so I’d prefer to see it advocated as part of a well-balanced exercise regimen, rather than a revolutionary approach that should replace your current one.

10 Replies to “Back to regular programming (intervals vs. endurance training)”

  1. So if i do the workout program insanity (which is a high intensity workout) and do distance runs while doing them everyother day will i be able to increase my 5k time?

  2. Hi Nick — thanks for the comment. I think the answer is probably “yes and no”…

    What you suggest sounds like a great way to get in shape and improve your overall fitness. It has a nice mix of intensity and sustained endurance training, and stimulates the whole body. Will it improve your 5K? Well, that depends on what your starting point is. Say you’re currently ONLY doing three distance runs a week, and you now add three Insanity workouts. There’s a good chance you’ll get a bit faster, but probably not as much as you’d expect. One of the key principles of training is specificity: the best way to improve running is to run more. Doing the Insanity workouts will make you better at the specific exercises you do in the workout — there will be certainly be some crossover because your overall aerobic fitness is increasing, but it’s not a direct outcome.

    So you have to think about your goals. If your top goal is to improve your 5K time, then you’re better off focusing most of your attention on running — i.e. instead of Insanity workouts, do intense running interval workouts. But if running faster is just one of your goals, along with getting stronger, healthier and so on, then Insanity (or other whole-body workout routines) is a great bet.

    Bottom line: if you do want to get faster as a runner, there’s no workout that’s more valuable or effective than a hard RUNNING interval workout — even just once a week. For example, you could replace one of your Insanity workouts with something like 10×1:00 or 5×2:00 hard with a minute or two rest (preceded by a warm-up and followed by a cool-down), and you’d get a lot of bang for your buck.

  3. Very interesting study. What I wonder when I see a study like this is who is the target audience – athletes, or untrained individuals? I would think that most athletes are already well acquainted with interval training which is at least relatively similar to HIT, so it’s not hugely revolutionary for their training regimes. And while this type of program undoubtedly improves health very efficiently, I can’t imagine many untrained individuals (let’s assume a sedentary individual with a BMI in the high 20’s or low 30’s), performing either HIT or hour-long runs at 80% HRmax multiple times/week for more than a few weeks – I certainly have no interest in doing either of those! These types of programs just don’t fit well into people’s lifestyles, nor are they particularly fun, and as you pointed out, there may be a real risk of injury. So while I find these studies interesting from a physiological perspective, I never really see where the public health impact is. Any thoughts?


  4. Good points, Travis. My sense is that studies like this aim to find the difference IN PRINCIPLE between the effects of intervals and long runs, rather than prescribe a step-by-step weight loss/health regimen. If, by using such extreme programs, then can establish some key principles (like, in this case, that you need both intensity and sustained effort), then you can incorporate those ideas in a more gradual progression of workouts.

    The problem is that I wonder whether throwing sedentary subjects into such a extreme program skews the results — e.g. by having the interval group only succeed in completing two-thirds of the assigned workouts due to injury. As you say, it’s hard to imagine many untrained individuals surviving such a program.

    That being said, I’ll take issue with one of your points: “These types of programs just don’t fit well into people’s lifestyles, nor are they particularly fun…” They definitely won’t be fun if you throw an untrained subject into the deep end (as this study appeared to do). But, as a semi-retired runner who once looked forward to the day when I’d never have to do another interval workout, I have to admit that I now realize that I do find them “fun”! There’s a great deal of satisfaction to be had from an intense workout, once your body has adjusted to the effort required. This isn’t a message that gets spread very much (most fitness programs advertise themselves based on how easy and effortless they are), but I think it’s a banner that ought to get waved a little more.

  5. I think your last point is brings up an important issue – most former athletes (which includes most exercise physiology researchers), have relatively positive views of structured, intense exercise. Exercise physiology has really developed around the science of athletes, and has only gradually begun to look at sedentary, unhealthy individuals. So it’s not a huge surprise that when we promote exercise, we promote the same model of exercise that we have enjoyed ourselves and which forms the foundation of past research in athletic populations (e.g. structured and intense).

    My concern is that many/most sedentary and/or obese individuals will not get to the point where they can get that satisfaction from an intense workout. It may be because they don’t have enough time to devote 45 minutes a day to structured exercise, or that they don’t have the resources to find a knowledgeable trainer, or that they get discouraged by discomfort early in the program, or because they simply don’t experience a runner’s high or any other positive affect from exercise, and never will. For one reason or another, the majority of people don’t stick with structured exercise programs for very long. This issue is especially pronounced in individuals who have been inactive their entire lives, and have often had very negative experiences with physical activity in the past.

    It just seems to me that it is better to adapt our exercise programs to meet the needs of those who need them the most, rather than asking them to adapt to a model of exercise that is really tailored to athletic performance. Not that we shouldn’t tout the many benefits of structured/intense exercise, but that we should realize that it’s a strategy that will probably only benefit a minority of individuals. (I realize this wasn’t the focus of the original post, but it’s an issue I struggle with whenever I see this type of paper, even those that I am working on personally).

  6. “Exercise physiology has really developed around the science of athletes, and has only gradually begun to look at sedentary, unhealthy individuals.” This is a really interesting point. My first thought was: Yes, people who’ve been sedentary their whole lives will struggle to adapt to a routine of vigorous exercise (unless they really have excellent support and persistence), but surely one key goal is to avoid letting another generation grow up with such minimal experience of hard exercise. If we set expectations too low, then we perpetuate the problem.

    Now that I think about it, though, you’re right that forms of exercise like hard interval workouts are a relatively recent and artificial construct. People a century ago (who, by and large, were much more physically fit) were more active throughout the day, but weren’t doing “high-intensity interval” sessions. So maybe it is silly of me to think that everyone would end up liking this type of routine if they just gave it an honest try for long enough — just because I happen to like it. (And it was hardly love at first sight for me — hard training was a necessary evil for many years, justified by the positive feedback I got from racing. It was probably close to the end of university that I finally realized that I enjoyed the workouts, and the associated camaraderie, for their own sake.)

  7. Interesting – thanks for the good info. Just been reading some work by Daniel Duane in Men’s Fitness that dovetails with this information – you might have a look.

  8. Thanks for this information. My love for long distance running as well as health concerns are supported by your words. As I see so many trainers taking seemingly untrained people through highly intense variable activities, I question the “new school” of thinking that interval training in the best and brightest way to train so many time conscious non-athletic people who are concerned for their health. I have also heard CPT making comments that having people train with long slower aerobic activity may cause them to loose business. Cardiac benefits, fat loss, and injury prevention seem to be secondary to business and muscle building. Despite the impressive VO2 max changes with interval training, the balance of taking off the fat and preventing injury need to be considered.
    Healthy regards, Maureen, RD, CPT

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