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| Image 1: Looks like humans are not the only lazy creatures, in these days of unhealthy convenience. |
Laziness, it seems, is utterly human. If you look around, these days,
it appears as if we were genetically programmed to be bone idle. And, from an evolutionary perspective, we may actually be. After all, moving around, hunting and gathering was an obligatory part of our lives in 99% of the human history. It was thus only consistent that our genes would tell us to sit down at the fireplace and relax, once we had found enough to eat on a given day... (un-)fortunately things have changed since those early days. Not only have we moved out of our caves, we have also found ways to radically reverse the ratio of activity to inactivity in our lives.
"Convenience" is the buzzword of the modern western civilization and the obesity epidemic is its unwanted consequence.A consequence, which is yet by no means inevitable. After all, we all know that getting our behinds off our couches and into the gym, and setting the dietary recommendations of the (fast-)food industry, ahh... pardon, the government at naught would solve the problem,
if ... yeah,
if there was not this aforementioned genetically programmed laziness that makes the couch so much more appealing to us than the hard benches in the gym...
Sacrifice 30min per week of your TV-time and live to see your grandchildren graduate A recent study from scientists from the United Kingdom does yet show that you could still spend more than enough time in front of your beloved television set, if you just performed what what Richard S. Metcalfe and his colleagues from the United Kingdom call the "
minimal amount of exercise for improving metabolic health" (
Metcalfe. 2011) - a
3x per week 10min exercise regimen with no more than two (yes, only 2x!) all-out sprints.
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| Figure 1: Outline of the training protocol, the black bars indicate all-out sprints at a breaking force equivalent to 7.5% of the individuals body weight (directly adapted from Metcalfe. 2011. Fig. 1) |
As you can see in the outline of the experimental protocol, the
29 healthy and normal-weight, but sedentary young (~23y) men (n=13) and women (n=16) did not even have to start with 2x20s sprints. They rather built up to it, by starting out with a single 10s all-out cycle-ergometer sprint at a braking force equivalent to 7.5% of their body weight in the first week of the 6-week study period and built their exercise capacity from there.
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| Image 2: "Cardio" does not have to be steady state. |
Note: If you have not read my
previous blogposts on HIIT, you may have missed the information that
interval training (not necessarily at the maximal intensity, though) is suitable for everyone - even heart disease patients (cf.
Interval, not Steady State Aerobics is the Way to Go - Even for Patients with Myocardial Infarctions!). This has been confirmed only recently by Neil A. Smart et al. who found that "[i]ntermittent exercise may improve functional capacity [of congestive heart failure patients] to a greater extent than continuous exercise" (
Smart. 2011) - and that despite the fact that both continuous (30min), as well as interval training (60min, 1 min cycling, 1 min rest) were performed at the same low intensity.
The rest of the 10-min exercise sessions, the subjects were pedaling along at 60W, which is about as much as it takes so that you do not fall off the bike, because of the lack of resistance that is required to stabilize yourself on the bike. The latter would have been tragic, at least if you are a man, because that would have counteracted the surprisingly (not for who has read about the
magic of HIIT here at the SuppVersity before) profound effects this regimen, for which the scientists coined the name "
reduced exertion high intensity training" (REHIT), had on the glucose homeostasis of the
male subjects.
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| Figure 2: Changes in VO2Max, glucose and insulin area under the cure in response to oral glucose tolerance test in men and women after 6 week of "reduced exertion high intensity training" (data calculated based on Metcalfe. 2011) |
As the data in figure 2 shows, the
statistically more than significant decreases in the area under the glucose (-12%) and insulin (-39%) curve (AUC) measured during an oral glucose tolerance test was
exclusive to the 13 male participants - and that despite the fact that both, male as well as female study participants exhibited similar improvements in their individual VO2Max (+15% in men; +12% in women).
(RE)HIIT only for men?As far as the underlying reasons for these gender differences are concerned, the scientists are pretty much at a loss, stating that this could be due to "the low statistical power of our study, with only eight female subjects performing the REHIT", " differences in metabolic perturbations during the brief high-intensity cycle sprints", and the 3-day delay after the last HIIT session before the glucose tolerance test was done (as a SuppVersity reader you will be familiar with the notion that the "
anabolic barn door" is wide open for 24-48h), so that "insulin sensitivity was improved in female subjects at an earlier time-point". Now, I do not want to sound like a himbo, but I would say that another observation the scientists made, provides a much better explanation:
[...] we observed that some of the female volunteers struggled with the transition from 60 W to the all-out sprints, and were unable to substantially increase their pedal frequency, and thus their power output during the sprints. This may have increased the aerobic contribution to energy supply and reduced glycogen depletion.
In other words, what was supposed to be a sprint turned out to be a sluggish ordeal. The slightly, but statistically significantly higher rates of perceived exertion (+10%) in the female study participants corroborates the assumption that the women simply did not burn enough glycogen. If we do now also consider the results of a 2008 study by Hagobia et al. who report that
[...] in women, exercise altered energy-regulating hormones in a direction expected to stimulate energy intake, regardless of energy status. In men, the response to exercise was abolished when energy balance was maintained.
It appears obvious that an
increase in pedaling frequency by adapting the resistance to the individual fitness levels
and dietary controls may be necessary to render this minimalist "REHIT" protocol productive for the fairer sex.
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| Figure 2: Comparison of changes in VO2Max, glucose and insulin area under the cure in response to oral glucose tolerance test subsequent to 6 weeks of REHIT, or 10 months of "classic cardio" exercise, or dietary intervention (data calculated based on Metcalfe. 2011 and Dengel. 1996) |
The comparison of this 6 week exercise program with the results of a
10 months intervention program in likewise healthy sedentary, but older men (45y) who exercised 3x a week for 40min (steady state) at 75-85% of their maximal heart rate, goes to show that
it would well be worth making the REHIT protocol work for women, as well (
Dengel. 1996). After all, the steady state endurance protocol in the Dengel study was not only four times more time-consuming (plus, the intervention period was 6.6x longer) than the modified HIIT protocol in the Metcalfe study, it also
failed to improve the glucose response to the oral glucose tolerance test and produced less pronounced improvements in insulin sensitivity (cf. insulin AUC in figure 3). The mild caloric reduction (-300-500kcal/day) that was imposed on another group of the study participants, on the other hand, yielded similar reductions in glucose and insulin AUCs as the REHIT protocol in the Metcalfe study that was accompanied by a body weight reduction of ~10%, a reduction in body-fat of -5.8% and essentially no loss in fat free mass!
Note: Unfortunately, Metcalfe et al. did not measure the body composition of the study participants. In view of the results of the Whyte study (
Whyte. 2010), I cited in the
Intermittent Thoughts on Healthy Weight Loss, where the participants lost -2.4cm of their allegedly obese bellies within no more than 2 weeks of doing HIIT, as well as the well-established correlation between insulin resistance and the size of your beer-belly,
it is very well possible that the male participants in the Metcalfe study will have lost some body fat doing no more than 8.67 minutes of all out cycling spread across 18 training sessions in 6 weeks... and if they didn't their diet probably was still too convenient ;-)
Taken together the results of these studies suggest that a) steady state aerobic exercise is pretty pointless, b)
even a minimalist HIIT regimen goes a long way, as long as c) you
really hit it hard and d) adhere to your regular (hopefully non-convenient) diet, or even better e) introduce a slight calorie deficit. In other words, without at least some "inconveniences" as far as nutrition and exercise are concerned, chances are that YOU will either remain or become one of the
34,004,946 obese human beings that are now populating a planet where the US alone spend 1,550,566$ per day on the detrimental health consequences of the"convenience" of its citizens (data from Obesity Statistics).
