Have you ever noticed when things become a buzz topic, people find themselves using terms without truly understanding what they’re talking about? I feel that’s currently happening with high intensity interval training or HIIT. Part of why I write is to simplify many of the fitness topics that either overwhelm or confuse many people. Today’s blog post is my attempt to de-mystify HIIT training. If I start to lose you, please hang in there, and hopefully it will make sense at the end.
To understand how we got here, you have to go back to the origin of cardiovascular training. Dr. Kenneth Cooper, founder of the Cooper institute in Dallas, coined the term aerobics in the late sixties. The scientific definition of aerobic work means in the presence of oxygen. In reference to exercise, it refers to those exercises which demand “large quantities of oxygen for prolonged periods and ultimately force the body to improve those responsible for the delivery of oxygen to the muscles,” as stated by Dr. Cooper. There are many benefits in training the body aerobically, or cardiovascularly. One of the main advantages is the ability of the body to improve its heart endurance. As time progresses with training, the heart muscle becomes stronger and more efficient in pumping blood to the working muscles. This is where steady state training became popular.
This is where I may get “a little in the weeds”, but I’ll do my best to keep it simple. When you begin an activity, the initial energy (up to 10 seconds) is provided by ATP/PCr (adenosine triphosphate phosphocreatine). This energy is stored in a cell and doesn’t require oxygen to burn (imagine 3-5 jumps as high as you can). If you continue to exercise for longer than 10 seconds, up to 90 seconds, your body will start to use the glycolytic energy system. This is when it will start to use stored muscle glycogen as fuel. This takes longer to do for the body and isn’t readily available (think of kettlebell swings for 1 minute). If you continue to exercise for longer than 90 seconds, your body will start to use the oxidative phosphorylative pathway. This fuel takes the longest for the body to deliver and is why intensity levels will start to drop off. Have you ever heard the term “you can’t sprint a marathon”? It’s in this process that the body will start to convert stored fat as a fuel source. That’s why the goal in the past was to see how long you can go. The longer you go, the more fat you could potentially burn, was the mindset. The confusing part is how much fat is converted. This process is very complex for the body and the body converts fat at a slow rate. The amount of fat used has widely been overstated.
Let’s fast forward 30 years to 1996 when Japanese scientist, Dr. Izumi Tabata, completed this now legendary study on high intensity interval training or HIIT. Tabata and his colleagues conducted a study that compared moderate-intensity continuous training (walking on a treadmill) at 70% of maximal oxygen consumption (VO2max) for 60 minutes, with HIIT conducted at 170% of VO2max. The HIIT workout consisted of eight, 20-second all-out exercise bouts, followed by 10 seconds of rest for a total of 4 minutes of exercise. These bouts were performed on an exercise bike. So to keep this simple, picture one group walking at a brisk pace on a treadmill for an hour, and another group performing these all-out 20 second sprints with a 10 second rest interval on a bike for 4 minutes. The study found that HIIT improved aerobic capacity to a similar degree as moderate-intensity continuous training, but also resulted in a 28% increase in anaerobic capacity. Those findings led to the development of a wide variety of HIIT programs. The HIIT group experienced better improvement cardiovascular and yielded a greater lose in fat (4 minutes compared to 60 minutes). Hence, the phenomenon of HIIT training began.
HIIT produced a bigger decrease in fat mass in less time. It was later determined that this was due to EPOC, or Excess post oxygen consumption. This has frequently been referred to as “the afterburn”.
As stated in Wikipedia: “In recovery, oxygen (EPOC) is used in the processes that restore the body to a resting state and adapt it to the exercise just performed. These include: hormone balancing, replenishment of fuel stores, cellular repair, innervation and anabolism. Post-exercise oxygen consumption replenishes the phosphagen system. New ATP is synthesized and some of this ATP donates phosphate groups to creatine until ATP and creatine levels are back to resting state levels again. Another use of EPOC is to fuel the body’s increased metabolism from the increase in body temperature which occurs during exercise.”
“EPOC is accompanied by an elevated consumption of fuel. In response to exercise, fat stores are broken down and free fatty acids (FFA) are released into the blood stream. In recovery, the direct oxidation of free fatty acids as fuel and the energy consuming re-conversion of FFAs back into fat stores both take place.”
I utilize the HIIT protocol in our studio for our Torch & DVRT workouts. We slightly modify the heart rate targets because we want to emphasize strength exercises which require some skill. Our new workout, Metabolic Disruption, is more of a true Tabata workout using less skill type movements which will allow more all out effort, without risk of injury.
That’s what the research tells us. Hopefully this was able to clarify what a HIIT workout is, how your body responds to them, and why they are beneficial.