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| Figure 1: Number [in millions!] of prediabetics and diagnosed and undiagnosed diabetics in the USA according to data from the American Diabetic Association from January 2011 (ADA. 2011) |
You probably remember
Wednesday's news-item on high-intensity interval training (HIIT) for cardiac patients - as it turned out,
even 2 weeks after myocardial infarction our central pump needs real exercise to get back in, or to get into even better shape. Today, I do yet want to go beyond infarction patients and address another, ever-growing sub-group of the self-perceived "victims" of the obesity pandemic, the type II diabetics.
About a month ago, J.P. Little and his colleagues from the
University of British Columbia Okanagan published a study in the
Journal of Applied Physiology (
Little. 2011a), the results of which confirm (once again) the unpopular hypothesis that getting your ass off the couch in order to work it off in the gym
hard (!) is the only way to treat a (largely) self-induced health condition that is plaguing 8.3% and threatening another quarter (79 million people with pre-diabetes) of the US population (
ADA. 2011, cf. figure 1).
In the Little study (pun intended ;-),
it took 8 type 2 diabetics no more than 60 minutes of intense exercise at 90% of their maximal heart rate (+another 60 minutes of rest in between intervals) to
[...] rapidly improve glucose control and induce adaptations in skeletal muscle that are linked to improved metabolic health
120 minutes (!) of which only 60 were spent doing 10x60s intervals on a cyclometer brought about
changes, no pharmaceutical (or even supplement) will ever produce (without significant side effects). 120 minutes spread across 6 exercise sessions in the course of two weeks, i.e. 3 sessions of 20 minutes per week - probably 20 minutes the majority of the 8 overweight (BMI 32.6kg/m²) diabetics would otherwise have spent on their couch in front of the TV, or - with comparably small benefit - trampling away at 65% of their VO2Max on a recumbent bike. With intervals at 90% of their maximal heart rate, however, the
[...] average 24-h blood glucose concentration was reduced after training (7.6±1.0 vs 6.6±0.7 mmol/L) as were the sum of the 3-h postprandial areas under the glucose curve for breakfast, lunch and dinner (both p<0.05).
More importantly, though,
HIIT training set the stage for future improvements by improving the capacity of the trainees mitochondria to handle / burn nutrients, with the
>3.5x increase in GLUT-4 acticity indicating a
profoundly increased capacity for glucose uptake and the
+20% increase in citrate synthase activity indicating an
increased capacity for substrate oxidation (energy usage) in the cellular power plants of the 8 diabetics (cf. figure 2).
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| Figure 2: Improvements citrate synthase, protein content of 70kDA subunit, complex III core 2 protein, complex IV subunit IV, mitofusion 2 and Glut-4 activity - all markers of mitochondrial capacity / efficiency - after 6 sessions of 10x60s cycling at 90% HRmax in 8 diabetic patients (data calculated based on Little. 2011a). |
These improvements, and this is a result from a previous study by Little's group (
Little. 2011b), were - at least in part - a result of the effects HIIT has on
mitochondrial biogenesis, of which Little et al. found that it is profoundly elevated in the first 24h after the exercise bout (3h post: +70%
nuclear PGC-1alpha/Tubulin, 24h post: +60%
whole muscle PGC-1alpha/Tubulin; +150% increase in p-p38MAPK) - and all that after a
single session of a all 4x30s all-out Wingate cycling tests separated by 4 min of rest).
Now, let me ask you:
Do we really ask too much of our fellow (and mostly ridiculously lazy) human being, if we ask them to invest one hour of their life per week to exercise into a, no, their healthier future? I wouldn't think so!
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Figure 3: Fat oxidation in kJ per minute during 60 min of cycling at 60% VO2Max before and after 7 sessions of HIIT training in eight healthy, normal-weight recreationally active women (Talanian. 2006).
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Metabolic benefits of HIIT training: Now, you may well ask yourself, why you should a give a damn about those changes, well... would it convince you, if I told you that in a 2006 study Talanian et al. were able to show that after 7 sessions of
serious HIIT training (10x4 min at 90% HRMax with 2 min rest between intervals)
the amount of body fat the eight female study participants burned during cycling at 60% of VO2Max was increased by 36% (
Talanian. 2006)? in other words, the HIIT sessions primed the bodies of the "recreatinally active women (22+/-1 yr old, 65.0kg body wt, 2.36l/min VO2peak) to burn more fat during subsequent cycling at the lower end of the "fat-burning zone"! As the data in figure 3 shows, this effect was partly, because the
subjects switched more readily into "fat burning mode" - a priming effect from the HIIT sessions.
HIIT, yeah... but how to find the right dosage?Both the Moholdt, as well as the Little study have shown that it does not take much to induce profound health benefits - but
what would be the optimal dosage for YOU, who, as a diligent student of the SuppVersity, are probably (or should I say hopefully) neither an overweight diabetic nor a cardiac patient?
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| Figure 4: Changes in body weight, body fat (%), peak lactate levels, perceived exertion (RPE) and VO2Max (rel. to body weight) after low intensity continuous training or three different HIIT protocols in recreational cyclists (data calculated based on Seiler. 2011) |
Apparently, a group of scientists from Kristinsand (again in Norway, where the descendants of the Vikings obviously are tough enough fore
real exercise ;-) asked themselves the exact same question (
Seiler. 2011). In the course of a 2 months study they had
29 male and 6 female recreational cyclists, whose VO2Max of 53+/-6 ml*kg/min were ~56% higher than those of the cardiac patients (after the intervention) in the Moholdt study, perform 2 HIIT sessions per week (plus 2-3 weekly low-intensity bouts) of one out of three different interval training programs:
4x4min, 4x8min, or 4x16 min at 94%, 90% or 88% of their respective maximal heart rates.
Hard, but neither torturous, nor time consuming The results, I have plotted in figure 4, confirm that HIIT must be hard, but neither torturous nor time-consuming. Or as the scientists put it:
The 4x8 min prescription induced greater physiological adaptation than both lower and higher intensity interval programs of 64- and 16-min total duration but was perceived as less stressful than 4x4 min at ~95% HR max . These findings suggest an important interaction between accumulated work duration and work intensity that can be optimized for inducing maximal physiolo gical adaptations at manageable RPE [rates of perceived exertion] in endurance athletes performing interval training.
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Image 1: Spinning at ~90% of your max heart rate
would be one way to do 4x8 intervals. |
On that note, it may also be interesting that in line with the
+91% increase in time to exhaustion Seiler et al. observed in the 4x8 HIIT group (vs. +12% in low intensity and +62% and +63% in 4x16 and 4x4 HIIT programs) and the
increased respiratory exchange rate Moholdt et al. observed in their study (cf.
Wednesday's news), A.D. Hafstadt and his colleagues from the
University of Tromsoe (
Hafstadt. 2011) have found in a mouse-model (where cutting out the heart and measuring its weight obviously is not so much of an issue as it would be with human subjects ;-) that despite
similar increases in the heart to body weight ratio (+10%), ...
[...] only HIT altered cardiac substrate utilization, as revealed by a 36% increase in glucose oxidation and a concomitant reduction in fatty acid oxidation, [...] improved cardiac efficiency by decreasing work-independent myocardial oxygen consumption and increased cardiac maximal mitochondrial respiratory capacity.
These findings lead the scientists to conclude that "
high intensity training is required for induction of changes in cardiac substrate utilization and energetics" and that these improvements may be at the heart (pun intended) of its "
superior" ability to increase aerobic capacity - or as, I previously phrased it:
HIT, not steady state aerobics, is real cardio training! You would not train a 20inch biceps with blue 2pound sand-filled plastic dumbbells, would you? I think, I will leave it on that, for today and wish you all have an
intense weekend (whatever your interpretation of that may be ;-)
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| Image 2: There is no one-size-fits-it-all HIIT training. |
Addendum of 10/01/2011: In the comments area, Oni posted a quite resonable question: "Doesn't HIIT usually employ shorter (1min) intervals? And how could 8 minute intervals, as in the Seiler study be feasible?" The answer to the first question is easy, as we just have to look at the words "high intensity" and "interval training",
now obviously no one questions that the regimen Seiler et al. used, had a high intensity (90%) and employed intervals - and I think Oni does not disagree on that, but rather implies that this type of training is
too intense and if the subjects had not been recreational cyclists, this could actually have been the case.
On the other hand, the results of the Seiler study also showed that
shorter intervals at higher intensity lead (in this subject group) to greater rates of perceived exertion. Now, I dare say that 95% of the trainees who are doing the standard ~1min bouts of
all-out exercise - are not going "all out" in the sense that they are scratching their real heart rate max. If they did, I am quite sure they would (in line with the results from the Seiler study) confirm that 8min @90% did not wear them out as much as 1min @100% of ALL OUT exercise at their max. heart. This leaves the question to be answered, whether 4 intervals à 8 minutes are optimal for everyone? And this is fortunately a question that is easy to be answered...
4x8 is obviously for "advanced" athletes (who have been practicing some type of endurance activity already). From my training experience, I know that untrained (or less trained) trainees sometimes do not even reach "target heart rates ~90%" before they feel so exhausted that they give up.
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| Image 3: The type of equipment you are using will also have an influence on optimal interval length; doing 8-min all-out intervals on the treadmill certainly are no viable option - even not for highly trained athletes! |
So what does that mean for your training, then? If you like doing the all-out (! don't forget to push yourselves!) 1-minute intervals, keep doing them. There are plenty of studies that confirm similarly beneficial effects on mitochondrial biogenesis with these protocols, e.g.
If, on the other hand, you are an (endurance) athlete wanting to improve your performance, the available data would suggest that intervals in the +4min range would be the way to go (
Seiler. 2004;
Driller. 2009;
Seiler. 2011), as they are more sport-specific. Overall, it is yet always about
balancing duration (individual interval length + number of intervals + rest days in-between) vs. intensity (heart rate) to find
your optimal HIIT protocol (
Gross. 2007;
Zuniga. 2011)
