|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)|
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 health120 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).
|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).|
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!
|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).|
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?
|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)|
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.
|Image 1: Spinning at ~90% of your max heart rate |
would be one way to do 4x8 intervals.
[...] 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 ;-)
|Image 2: There is no one-size-fits-it-all HIIT training.|
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.
|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!|
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)