Science Behind Sprint Interval Training

I am a huge proponent of sprint interval training. That is an explosive repeat effort done for a short period of time usually 20-30’s at 100% intensity. This can take the form of Running Sprints, Rowing Sprints or Cycling Sprints. Sprint Interval training (SIT) is a form of High intensity interval training know as HIIT.


The science behind Sprint Interval Training (SIT)

In a previous blog post I wrote… “Jens Bangsbo performed a study in 2009 showing that if you want to run, cycle or swim faster at any distance, you have to train at a pace that is almost as fast as you can move.  In 2005 and 2006 Burgomaster et al performed studies looking at the effect of sprint training on endurance. They concluded that short sprint interval training (approximately 15 min of intense exercise over 2 wk period) increased muscle oxidative potential and doubled endurance capacity during intense aerobic cycling in recreationally active individuals. In 2005 Gibala reported that 30 second bursts working at 250% of VO2 max had significant improvements on endurance.”

More Mitochondria More Citrate Synthase

 Wait but there is more, In a study by Little et al (2010) they demonstrated that a practical model of low volume HIIT is a potent stimulus for increasing skeletal muscle mitochondrial capacity and improving exercise performance.  Mitochondria are the place in your muscle cells where carbohydrate, fat, and protein can be broken down in the presence of oxygen to create the energy you need to exercise. To put it simply, the more mitochondria you have, the more energy you can generate during exercise, and the faster and longer you can run, fight, cycle, pop and lock or swim.
HIIT training sets the stage for improvement in the long term by improving the capacity of the trainees mitochondria to handle / utilise nutrients, with an increase in GLUT-4 activity (GLUT4 is the insulin-regulated glucose transporter) 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), taking this into account its an excellent training method for diabetics and the over weight. The increase in citrate synthase also means higher turn over of the krebs cycle which means more energy.

Mitochondria are inherited from your mother, do them proud


Increase Muscle Hypertrophy

Sprint training also helps with musclular hypertrophy (growth). In a study by Esbj√∂rnsson et al (2011) they concluded that “repeated 30-s all-out bouts of sprint exercise separated by 20 min of rest increases Akt/mTOR signalling in skeletal muscle. Secondly, signalling downstream of mTOR was stronger in women than in men after sprint exercise indicated by the increased phosphorylation of p70S6k.” MTOR is Mammalian target of rapamycin,  a protein kinase that regulates cell growth and protein synthesis, increased signalling means increase protein synthesis. While this protocal was unusual (I would’nt recommend resting 20 mins) it is compelling that women achieved better results than the men.

An extreme application of HIIT

In a 2011 study in the Journal of Clinical Rehabilitation, research had patients that had previously suffered myocardial infarctions (heart attack) do sprint interval training and compared it to a control group of did the recommended 60 minutes of steady state exercise. Can you guess who saw the most improvement? The HIIT trained group! Their VO2 maxed were over 2.5 time higher than those who did the regular protocal. A study by Smart et al (2011) Also saw similar results. While the medical establishment still thinks that this maybe to much for a cardiac patient the evidence seems to be creeping towards the idea that the heart needs some real stimulus to get back into proper working shape.

That judo study 

I blogged before about a korean study on judo players, that under took Sprint Interval Training as part of their off season conditioning. The results were compelling “anaerobic peak power and mean power in SIT group was significantly increased by 16% and 17% at 4 weeks and by 17% and 22% at 8 weeks compared to baseline values.” Additionally the blood lactate was lower and ability to clear metabolites was higher in those who did SIT.  These are changes in the capacities of high level athletes who are peaking in terms of VO2 max capabilities, found more room for improvement by attacking their top end anaerobic power out puts for repeat attempts.

Add Caffeine for a powerful fat loss effect. 

An Australian study had athletes use caffeine and HIIT, one group doing just HIIT. they found the caffeine group saw greater fat loss than those who did not. They concluded that “Caffeine and HIIE, with subsequent TTE exercise, may be an effective method at stimulating lipolysis for potential increased fat oxidation following exercise. Furthermore, enhanced energy expenditure following exercise suggests this protocol is beneficial for optimising energy deficit and potential use in weight management program.”

How many Intervals?

Personally for athletes I prefer 6-8 x 30 with 3-4 minutes rest between intervals. More advanced trainees can work up to 8-12 or 2 x 8 intervals. One study has shown you can get away with as little as 2 x 30 second sprints twice a week and still see improvements in VO2 max. You can sprint on a treadmill, track, a rower (my preference) or a properly set-up spin bike. The thing that links all of this is every sprint MUST BE 100% EFFORT, no half efforts will do. One observation is that track sprinting appears to be stressful in terms of soft tissue injury, a 2012 study released just this month (feb 8th) confirmed my suspicions. For this reason I prefer to cycle tracking sprinting with other modalities, after-all its the effort not the method that is important.

Protocals used to achieve increased mitchondrial density, citrate synthase and fat loss.

8-12 x 60 seconds – Little. 2010
7 x 30 seconds – Psilander. 2010
4 x 30 seconds – Giballa. 2009
6-8x 30 seconds – Kim 2011

Hopefully ive provided you with an insight into this excellent conditioning method. That saves time and works very quickly, all you or your athletes/clients need to do is bring a willingness to put 100% into every effort.

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