What is HIIT and SIT??

Have you every met someone who loves to run?  I mean the guy that gets up every morning and jogs for an hour before work.  Or the girl that gets some bad news and goes on a 10 mile run to let off steam.  Are you one of these people?  If you are, then this article is NOT intended for you.  Running is no longer considered the ideal form of exercise, but some runners just need to run.

This article is for the rest of us.  The person who buys running shoes based on style rather than performance.  Most people dislike cardio.  I definitely do.  It is dull and tedious and seems to go on forever.  But……. cardio has its benefits.  That’s why doctors and fitness experts have been cramming it down our throats for so many years. Cardiovascular activity increases bone density, and reduces your risk of heart disease and some types of cancer. It has substantial benefits for the mind; it helps to reduce stress by stimulating the release of endorphins and provides relief from depression and anxiety.

But, traditional cardio can be a huge time commitment.  If you have a busy life, trying to carve out thirty minutes to an hour out of your day can prove difficult.  And, let’s be honest.  For most of us, it is just not that fun.   But, what if there was a way to make cardio more exciting, more effective and most importantly SHORTER?  Well, let me introduce you to HIIT and SIT.

What is HIIT & SIT? 

High intensity interval training (HIIT) and sprint interval training (SIT) are relatively newer forms of cardio devised for their effectiveness and efficiency.  They emerged out of our constant quest to find the minimal effective dose of exercise required to achieve a desired health benefit.   Exercise less and achieve the same benefits?  Sign me up!


HIIT is a training technique where you give “nearly” all of your effort in quick, intense intervals of exercise, followed by brief periods of recovery either in the form of less strenuous activity or rest.  An example would be alternating running and jogging on a treadmill.   Pretty straightforward.   One of my favorite forms of HIIT is called Tabata Sprints.  This was based on the research done by Dr. Izumi Tabata.  Tabata sprints consists of twenty seconds of near maximum output, followed by ten seconds of rest, repeated eight times without pause for a total of four minutes.   You heard me…. Four minutes!   You can use virtually any kind of exercise in this format, or mix it up!  For example, push-ups, followed by lunges, followed by burpees, followed by mountain climbers…. then repeat.   You get the picture.  Sounds simple…… and it is.  But, it this simple 4 minute routine will have you winded in no time.


SIT is very similar to HIIT, but even less time consuming.   In SIT, you give a “supramaximal” effort for even shorter periods of time followed by longer recovery periods.   What does supramaximal mean?  Imagine someone in a hockey mask chasing you with a chainsaw.  But, does it work?  Why yes…. Yes it does.  Dr. Martin Gibala showed that as little as 3 minutes of SIT a week was as effective as 150 minutes of moderate cardio in improving aerobic fitness, increasing mitochondria density, and improving glucose sensitivity.   Do you have 3 minutes to spare? (To be completely honest, Dr. Gibala’s “1 minute workout” does take 30 minutes a week with the warmup, recovery time, and cooldown…… but still)

HIIT & SIT is not only highly convenient it’s also extremely effective at burning body fat and developing fitness levels. So what is the science behind this? 

Mitochodria Biogenesis

 You will hear me talk about mitochondria a bunch.  I hoard them whenever I can….. through proper nutrition and exercise.  Mitochondria are the microscopic power centers in your cells.  They convert food into chemical energy (ATP) among other things.  I won’t bore you with the various molecular pathways that I had to learn in medical school (it left me with PTSD).  But, the bottom line is that you want lots of mitochondria……. and you want them all to function well.

When you perform interval training, you actually increase your production of mitochondria.  The body does this in response to the demands being placed on it.   It is the degree of “stress” that is placed on the body that is the key.  That is why short bursts of SIT work just as well as traditional cardio.  Start with “supramaximal” efforts, even if it is for a few seconds.  Then build up tolerance over time.  

Improved Aerobic capacity (VO2 max) 

VO2 max refers to the maximum amount of oxygen that a person can utilize during maximal exercise.  This is considered the gold standard when it comes to quantifying a person’s cardiovascular fitness and aerobic endurance.  Basically, you measure a person’s oxygen consumption during strenuous exercise.  Oxygen consumption follows a linear relationship to increasing degrees of exercise….. to a point.  When that oxygen consumption plateaus, then you have essentially reached your VO2 max.  Clear as mud?  Understanding the science is not all that important.  Just know that HIIT and SIT improves cardiovascular fitness and aerobic endurance just as well if not better than traditional cardio.

VO2 max is best measured in a fitness laboratory, but there are now calculators as well that are fairly reliable and reproducible.

Improved Insulin sensitivity

You are going to hear me talk about insulin sensitivity as much as mitochondria.  Insulin resistance, in my mind, is literally the root of all evil…..  It is the precursor to diabetes and the cause of most forms of obesity.  It is highly highly destructive.

Insulin resistance is largely bought on by a combination of a sedentary lifestyle and a high intake of sugar and processed foods.  Luckily, interval cardio along with a lower carbohydrate diet can completely reverse this process.

 What are other benefits of HIIT and SIT?

  1. Accelerated Fat Loss
  2. Increased testosterone and growth hormone
  3. Decreased Ghrelin levels and increased Leptin levels

Fat Loss

High-intensity interval training pushes your body towards its metabolic limits (so as hard as it can go) and the low-intensity intervals give it chance to recover and you can get some oxygen back into your blood. Because of the elevation in your heart rate, your body will undergo increased resting metabolic rates for up to 24 hours after exercise – so this means you are effectively burning extra calories for all this time after.

A study conducted by the University Of Western Ontario discovered that performing 4 to 6, 30-second sprints burns more fat than 60 minutes of incline treadmill walking. 1

High-intensity exercise can effectively burn more calories than steady state, low-intensity exercise, and as fat loss is dictated by energy balance the advantage of HIIT or SIT is clear. If you have a busy life and get bored easily by cardio then these are excellent options to destroy that stubborn body fat!

Testosterone and Growth Hormone levels

Both are increased after HIIT and SIT.  In fact, your human growth hormone (HGH) increases as much as 450 percent during the 24 hours after you finish your workout.   HGH increases caloric burn and slows down the aging process.  Testosterone contributes to muscle gain and weight loss, in addition to countless other benefits.

Leptin and Ghrelin

Ghrelin is the hormone that makes you hungry.  So……. we don’t want this.  Leptin makes you full.  So……. we DO want this.  High intensity training can make both happen!

If you haven’t tried HIIT or SIT yet, it’s time you started so you can begin to reap the rewards!

  1. Run sprint interval training improves aerobic performance but not maximal cardiac output.  Macpherson RE1, Hazell TJ, Olver TD, Paterson DH, Lemon PW.

by | Jul 9, 2018

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