Understand high intensity interval training.

High intensity Interval training (HIIT) refers to quick bouts of high intensity exercises with low-effort rest intervals which enables anyone to increase the intensity of the exercise workload. The term “High-intensity” is relative to an individual’s level of fitness and dependent upon one’s tolerance to exertion. At the same time, we need to understand the term “High intensity”. This term is used in the scientific literature to describe intensity ranging from as low as 85% of maximal oxygen uptake (VO2 max) to as high as 250%.  When you are exercising above 100% VO2 max, it is termed “supra-maximal"


VO2 max is the measurement of the maximum amount of oxygen that an individual can utilize during intense, or maximal exercise.

Because of the wide range of intensities reported in the research for HIIT, the duration of the exercise interval can also range from as low as six seconds to as high as four minutes and sometimes even longer. The recovery interval used in HIIT can vary considerably and can be an active recovery or a passive recovery.


Passive recovery means stillness and inactivity. By contrast, active recovery means being active in a way that promotes recovery rather than fatigue.

What happen when you realize a high intensity interval training (HIIT).

Interval training works both the aerobic and the anaerobic system.  During the high-intensity efforts, the anaerobic system uses the energy stored in the muscles (glycogen) for short bursts of activity. Anaerobic metabolism works without oxygen, with a by-product name lactic acid.  As lactic acid builds, the athlete enters oxygen debt or ECOP, and it is during the recovery phase that the heart and lungs work together to "pay back" this oxygen debt and break down the lactic acid.


ECOP: Excess post-exercise oxygen consumption (ECOP, informally called after run)is a measurably increased rate of oxygen intake following strenuous activity.


To pay back this oxygen debt, the metabolism continues to work during  this post‐exercise phase. (Recovery phase)  When it comes to replenishing the energy stores of the body, it makes sense that if one were to predominantly burn glycogen as a fuel during a HIIT workout, (Anaerobic system used) the body would need to put back those glycogen stores to be ready for a subsequent similar activity. Consequently, it would further make sense for the body to utilize fat while it is accomplishing the glycogen “put back.” It has been demonstrated that following high‐intensity exercise, but not low‐ intensity exercise, oxygen consumption remains elevated above post exercise phase at three hours post‐exercise; further, at this 3‐hour time point, the rate of fat oxidation was higher after high‐intensity exercise as compared to low‐ intensity exercise.

Why we still focused the spotlight on the continuous endurance training.

With all the information, research and cases showings that HIIT is an alternative to improve cardio-vascular system, we still focus the spotlight on the continuous endurance training.  To understand the reason why we relate cardio or aerobic exercise to low and moderate continuous training, we need to start with the running craze of the 70’s, which made jogging a popular activity. This period coincided with the developing sport science discipline.  The metabolic respiratory equipment at that time did not have the ability to measure oxygen concentrations from small volumes of expired air and it was less complicated to measure expired air from one long bout of continuous exercise rather than multiple bouts of high intensity exercise.   This biased the research toward activities that were of a long, continuous duration and, by natural default, activities that were of low to moderate intensity.  As a consequence, the published research from the late 70’s to the mid 90’s which clearly resulted in a disproportionate focus on low to moderate intensity continuous training, had a profound influence on the medical community, the fitness industry, and even the sports conditioning world.


Low and moderate intensity continuous training Ied to it being labeled “cardio” or “aerobic” exercise and to the thought process that this type of training, and only this type of training, would positively condition the cardiovascular system. This same process and resultant thinking played out with the research examining fat metabolism and “burning” fat stores

A common sense viewpoint.

We can look at High intensity interval training from a common sense viewpoint to explain why interval training trumps low and moderate continuous training every time.  In primal times, humans, for the most part, would not have moved long distances by running slowly or “jogging” as our modern world likes to call it. Throughout a day, short, vigorous bouts of activity would be required for gathering, carrying, digging and escaping danger. We can easily imagine that jogging through fields and forests would not be a particularly effective strategy.  At the same time, the biochemical make‐up of human muscle fibers is not comparable to truly superb endurance creatures. In the animal kingdom, humans, are a long way from, for example, ducks that can fly vast distances without breaking a sweat.  Another common sense perspective is to think about the activity profiles of young children. An observational study of children playing under free-ranging natural conditions showed a pattern of very short bursts of intense physical activity interspersed with varying intervals of low and moderate intensity. It seems to me that we are naturally wired for HIIT rather than Low and moderate continuous training. The same observation can be made in the vast majority of sport. They are for the most interval based, meaning that the activity comprises short bursts of high intensity effort fallowed by rest or recovery period of low intensity efforts.


Continuous based efforts Sports 

Distance running, cycling or swimming, Nordic Sky


Interval based efforts Sports

Football, baseball, tennis, golf, basketball, hockey (ice or field ‐ still the same), soccer, rugby, skiing, snow‐boarding, volleyball, and . . .


Researchers have compared these two types of training regimes, side by side, the HIIT has always matched LMICT, and usually produced more favorable results, with a much lower investment of time. So, clearly, this message is extremely important given that the time commitment is invariably given as the main excuse for not starting or sticking with an exercise program. When you engage in a high intensity interval training program you will be able to improve your hearth and performance.