“Reduced intensity” HIT: the Flutter of exercise


As of September 2017, new Sweat Science columns are being published at www.outsideonline.com/sweatscience. 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)


Anyone remember this Twitter spoof video from back in 2009, when Twitter was just catching on? It’s all about “Flutter,” which “takes microblogging to the next level” by restricting the length of each message to 26 characters instead of 140 characters. Nanoblogging, they call it.

I couldn’t help thinking of this when I read this new study in the European Journal of Applied Physiology about “reduced-exertion high-intensity interval training” (REHIT). Over the last few years, high-intensity interval training (HIT) has gotten a lot of attention as a time-efficient way of getting many of the health benefits of aerobic exercise. There are various protocols — the classic is four to six 30-second sprints with 4:00 easy jogging or cycling to recover between each one; another common one is alternating bouts of 1:00 hard with 1:00 easy. These workouts seem to be highly effective at improving traits like insulin sensitivity. But there’s a catch, according to the authors of the new study:

However, whilst these observations [about HIT] are interesting from a human physiological perspective, their translation into physical activity recommendations for the general population is uncertain for two reasons. First, the relatively high exertion associated with ‘classic’ HIT sessions requires strong motivation and may be perceived as too strenuous for many sedentary individuals. Second, although a typical HIT session requires only 2–3 min of actual sprint exercise, when considered as a feasible exercise session including a warm-up, recovery intervals and cool-down, the total time commitment is more than 20 min [gasp!], reducing the time efficiency. Thus, there is scope for further research to determine whether the current HIT protocol can be modified to reduce the levels of exertion and time-commitment while maintaining the associated health benefits.

In other words, the “140 character” version of exercise is still too damn long, so we need to shorten it to 26 characters!

So here’s the protocol they used. The subjects (29 sedentary young men and women) did three workouts a week for six weeks. Each of these workouts was exactly 10 minutes long, and consisted almost exclusively of “low intensity” cycling, at 60 W. This is very easy. During each 10-minute workout, the subjects incorporated two 10- to 20-second hard sprints. That’s it. Lo and behold, the men in the REHIT group increased their insulin sensitivity by 28%. Strangely, the women didn’t improve — it’s not clear why there was a gender difference. It may be that the very short sprints are most useful for men, who tend to be more powerful and thus are able to burn through more glycogen in a short time.

Anyway, there you have it: REHIT, the Flutter of exercise. I have to admit, part of me finds this a little funny. Soon we’ll be doing studies to show that, if you’re really and truly unfit, just blinking your eyes will allow you to make “measurable gains” in fitness parameters. On the other hand, the barriers to getting people to exercise really are tough to beat. I’m always encouraging my parents to do a little HIT rather than just stick to low-intensity activity — and they do, but they’re rarely motivated to spend more than 10 minutes in total. So it’s encouraging — and useful — to know that even a very minimal bout of high intensity will help. In the end, though, the message is pretty much what we already knew: every little bit helps — but more is better.

17 Replies to ““Reduced intensity” HIT: the Flutter of exercise”

  1. Exercise is hard work be it at a high intensity for a short time or low intensity for longer and without some greater motivation then, “it is good for you” most people just won’t do it. I was like that for 20 years of my adult life and I think the thing that tripped the light in my head to keep the “exercising thing” going was an interest I developed in “running form” and how it can make you fast faster. In other words I was duped into it. So from a personal stand point I can attest to the fact that duping people into exercising does work and then the next trick is to keep them exercising after they figure out that everything they were told to begin with was a load of cr*p. A few ways to do this is by having them invest hard earned money in sport appropriate clothing and equipment, encouraging them to make new friends with the same athletic interests and awarding them with participation medals at every event they show up for. Once again it worked for me so it should work for them also.

    And how about visualization exercises http://sportsmedicine.about.com/od/sportspsychology/a/thinkstrong.htm
    , aren’t they suppose to make “measurable gains” also?

    Alex what you need to do is write an article(under a pseudonym) about how someone trained for and ran a marathon simply by thinking about it 10 minutes a day then later added 100-ups to the end of his routine and ran his next marathon faster then later added 10 minutes HIT to his training and set another pr. Make sure to also add things like he was admired by all and looked great in his jeans to boot. Duping people Alex, it’s the only way.

  2. What about the Tabata method? A protocol where 20 seconds of all-out activity and 10 seconds of rest is repeated 8 times. It’s been shown to improve insulin sensitivity and anaerobic capacity. That’s a 4 minute exercise bout coupled with a 10 minute warm-up, which gives you less than 15 minutes total!
    I think the biggest issue is getting unfit individuals to truly work at “maximum” capacity. I feel that most untrained folks don’t know how to reach that intensity or motivate themselves to work that hard.

  3. Just wait ’til the crossfit folks get a hold of this. Pose method sprints in Inov-8s for everyone! (After kipping pullups and power cleans, of course.)

  4. I was wondering when you would comment on this one and what your angle would be. I tend to be more encouraged by it and it’s implications. We need to get people moving more but if we can throw in even some short intense episodes there will be bigger benefits. Walking upstairs for example a few times a day could be regular intense stimulus not least for insulin sensitivity for many people.

  5. On a more serious note, I really doubt that the total workout time is what makes it difficult for some people to stick to an exercise programme. More likely it is that hurting yourself every other day, whether it is 10 minutes or an hour, isn’t all that rewarding if it is for an abstract statistical reward like 5.3 added Quality Adjusted Life Years per averted stroke.

    The difficult part is to make exercise either fun (the point of game sports, and in my opinion the clever thing about Zumba) or an integral part of daily life (such as cycling to work).

    If we really want to get the least active part of the population to stick to a minimal exercise programme, I propose that people sprint instead of walk from the couch to the fridge for a beer (Reduced Exertion Full Intensity Leisure-time Liquification).

  6. @RH,
    Right on. the vast majority of people will not exercise at all if it isn’t built in to the life style. Ditto diet. the “Aerobics revolution” was a big fail. Even in our appearance obsessed society, everyone wants a magic pill, and that’s probably what it will take.

  7. @nigel: YES!!! That’s hilarious — I’d forgotten about that scene. Everyone, do yourselves a favour and click on the link in nigel’s comment. It makes my point much more succinctly (and humorously).

  8. @RH: You’re a master of acronyms! 🙂

    @Chris: First off, congratulations on being honoured by Outside Magazine as one of the Top 10 Fitness Blogs! A very prestigious honour, I hear. 🙂

    In terms of being encouraged by this research — yes, I understand what you’re saying, and largely agree with you. As I mentioned in my post, I’ve managed to convince my parents to throw in a few higher-intensity bouts into their exercise regimens, but they still fall far short of the dictates of standard HIT routines. And they’re definitely not alone. So it’s interesting — and encouraging — to know that very, very short bouts of vigorous exercise (even just 10-20 seconds) really do help. For them, REHIT is more realistic than HIT.

    The one caveat I’d raise is the same general point that EJ, RH and Griff are getting at in various ways. The basic assumption underlying HIT is that “People want to exercise, but they just don’t have time. If we figure out a shorter way to get the same benefits, everyone will do it.” But is this really true?

    Take a step back by a couple decades, when the basic public health assumption was “People don’t realize how important exercise is, but if we explain to them all the benefits that exercise offers, and all the horrible things that will happen to them if they don’t exercise, then they’ll start exercising.” But that didn’t really work. Now everyone knows what they “should” do — but fewer people than ever actually do it.

    So HIT is another worthwhile attempt to reduce the barriers to exercise, and I’m sure it has worked for some people — but definitely not all. Now REHIT lowers those barriers even more. But is there anyone who’s going to say “I was way too busy to make time for 15-minute workouts, but 10-minute workouts are a totally different kettle of fish — I can make time for those!”

    Okay, I’m rambling a bit here. The basic point is: this research is interesting and valuable in that it encourages us to value every little bit of exercise. But contrary to the implicit hopes of the researchers, I don’t think the specific REHIT protocol is going to catch on as a more palatable alternative than plain-vanilla HIT, because anyone who couldn’t make time for HIT is being limited by factors other than the availability of time.

  9. “. . . Now REHIT lowers the barriers even more . . . and encourages us to value every little bit of exercise.”

    But according to the research, it’s ineffectual (at least in raising insulin sensitivity) for half the population. WHich makes me wonder: is there good data on the efficacy of HIT on women (v. men)?

  10. @alex

    first of all, thanks for pointing out that I made the Outside blog list! I do not feel that I deserve it at all compared to some of the others there, not least your own work. I just list and point to things that I have found interesting. The level of analysis that you and others provide is far beyond the casual references that I put up.

    Secondly, with respect to this study I take the point you are making. I suppose I see it and for me it is a motivation….I think about adding a 10 second sprint to my 10 minute walk at lunch time for the insulin sensitivity benefits, but that is different from getting the motivation to do the walk in the first place.



  11. @kiki: This is a great point, which I should have discussed in more detail. Previous studies of classic HIT haven’t found any differences in gender response (according to this paper). The authors suggest two explanations for their results:

    (1) It was a fluke. After all, the low overall numbers meant that only eight women performed the REHIT program. A couple of duds among them might have been enough to skew the results. Of course, if you accept that, then you have to accept the possibility that the POSITIVE results among the men might also have been a fluke!

    (2) “[I]t can be speculated that differences in metabolic perturbations during the brief high-intensity cycle sprints may contribute to the observed gender difference, as women have been shown to break down up to 50% less glycogen during a single Wingate sprint.”

    I would translate that to mean that, for very short bout of sprinting like the REHIT program, you have to be pretty powerful in order to burn lots of glycogen within that 10-20 sec window. So men are more likely to be able to reach the necessary high power output than women, making them more likely to benefit from the REHIT protocol. But this is all just speculation.

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