High Intensity Interval Training
It astonishes me how for some reason one article or video can catch on and spread like wildfire to multiple traditional media and social media outlets in just a few hours. Have you guys read this one about sprint training?
A couple of weeks ago, this topic was all over various outlets, with the conclusion that HIIT can result in damaged mitochondria and decreased capacity to fight free radicals.
There are hundreds and hundreds of research papers on HIIT and somehow, this one magically becomes the golden child and goes viral?
Let us talk about HIIT.
What is High Intensity Interval Training?
High Intensity Interval Training training (HIIT) is exactly what the name says it is; an exercise modality that utilizes short bouts of high intensity exercise alternated with periods of low intensity exercise. There are various techniques and methods (eg Tabata, Fartlek) that have been shown to improve performance, even in highly trained athletes.
The benefit of this type of training is that you are pushing your body to create energy (ATP) using systems that do not rely on oxygen. Aerobic respiration (oxygen consuming) can only provide enough ATP for lower intensity exercises, so we need these backup systems to kick in when the intensity ramps up.
These anaerobic systems, however, create byproducts which are often considered to be "toxic" (eg lactate). But.....the body adapts. There is evidence that the body has many positive short term and long term adaptive responses to the presence of anaerobic byproducts:
-blood flow increases to areas of high concentrations of toxic byproducts (reactive hyperemia)
-the formation of new capillaries is induced, allowing for increased blood delivery long term
-enzyme concentration and function improves for both the aerobic and anaerobic systems
-some people even believe that the quality of muscle fibres change according to the type of stress they are under
The presence of these "toxic" byproducts creates a positive adaptation.
Does High Intensity Interval Training Work?
It is not to say, however, that continuous intensity exercise programs are not necessary. Continuous intensity programs have been shown to have better long term benefits in weight control and resting heart rate than HIIT.
What about that research paper that said HIIT is bad for you?
I would be surprised if any of the journalists who reported on this article actually sat down and read the paper.
Give it a read: http://www.fasebj.org/content/30/1/417
To summarize the article quickly, 12 "untrained" Swedish young men were put through high interval training programs, performed on a leg cycle and an arm cycle machine. After the training periods, various tests were completed, including biopsies from the arms and the legs. The tissues were then broken down and various tests performed. The researchers were interested in mitochondrial function and enzyme levels after HIIT training. For those who do not remember, the mitochondria are the "energy cells" and are where various processes occur that create ATP.
Now, I have a kinesiology degree from a really tough program where we had to learn very advanced human physiology, anatomy and biochemistry, but to really understand this paper you need a doctorate. To truly critique the isolation techniques and assays, you have to know lab research. I sure don't.
But I can read the article and look at the methodology and question things.
The first thing that stands out is that there was only one group being studied (no control). Would the findings be different on trained subjects? Or women? Or older men? Or non-Swedes?
Then, there is the way they applied the interventions. There were two exercises that were performed, one on a bicycle and then another on a machine that you pedal with your arms. This was to be able to compare two different muscle groups. Who in the world rides their bike with their arms? Most people run, walk and ride bikes, so they have some sort of familiarity with the leg test, but peddling with arms? I have always questioned the validity of comparing the arm cycle test to the leg cycle test.
And finally, the conclusions: there were two totally different results when the arms were compared to the legs. The legs actually showed what I consider to be positive adaptations: there was in increase in mitochondrial density and the mitochondria were functioning at lower rates. That means the body responded by increasing the amount of power cells, and decreasing the amount of power drawn from each one, meaning....that when the intensity ramps up again, there are more cells with more reserve to draw from. That is good, right?
But the arms told a slightly different story. There were reductions in an enzyme (aconitase) which is believed to play a role in how well the mitochondria respond to oxidative stresses. This reduction, however, was not found in the legs muscles, because there was an increase in mitochondrial density.
Why would there be a difference between the arms and the legs? Well, the authors did not have a concrete explanation for this, but did mention that perhaps the legs were used to that kind of training and the arms weren't, so the two muscles actually experienced different oxidative stresses during the study. Kind of a big variable don't you think?
So how did this article gain so much traction?
I blame bias.
The authors demonstrate bias right from their title. Their paper found that, "HIT increases work capacity, mitochondrial density, and oxidative enzyme activity, without change in myosin heavy chain composition." Basically the subjects could work out harder, had more energy cells, and were able to burn oxygen better, all without changes in the actual muscles.
The study also only showed negative results in the triceps, and there is question whether the intensity levels were truly the same between the arms and legs......yet the title was:
"High-intensity sprint training inhibits mitochondrial respiration through aconitase inactivation"
Catchy! But..... deceptive....because that statement only represents half of their results, and the rest of their data had findings that can be interpreted as positive adaptations. (My own bias showing through)
But this is how researchers can draw attention to their papers, and why people catch on to specific articles but not others; the persuasion of a catchy title and a biased abstract. The huffington post article even made the leap between free radicals and cancer.....so HIIT will cause cancer??? Comon!!!
To really understand the article, you have to read the whole thing.
On similar note, check out this great Ted Talk on publication bias.
What can we conclude about HIIT?
If you are considering starting a HIIT program, get proper training. Go to a gym that has actual kinesiologists as training staff. Anyone can do a 6 week course online and call themselves a trainer, but a kin degree is a totally different thing.
If you have any health concerns or have answered yes to any of the questions on the PAR-Q (if your trainer hasn't asked you to fill one out, ask yourself why), talk to your physician before starting any program.
And work your way up!
It is unhealthy and unsustainable to go from zero to hero overnight. Do not just go from couch sitting to crossfit or from sedentary to sprinting. It is a sure way to get injured and to hate what you are doing.
Thanks for reading,