The 5 Principles to a Great Body Part 5 High Intensity Interval Training

Posted: Tuesday, 20 March 2012 by Strength&Nutrition24/7 in Labels: , ,


High intensity interval (intermittent) training (HIIT) is an effective tool for weight loss, and fat metabolism. Weight loss and cardiovascular fitness both respond more favourably to HIIT then long duration cardio. However, just as noted in part 4, the general population has the belief that long distance exercise is the most effective form of cardio and fat loss. It is your job as fitness professional to have an understanding of HIIT training in order to educate and sell the benefits of it to your clients. The main reasoning to this belief is due to the well established understanding that as intensity of training increases, the dependency on carbs for metabolism increases, thus, reducing fat metabolism. This belief is well founded and indeed correct, but people focus too much on the initial fat metabolism and do not understand that as intensity increases, the caloric expenditure increases overall exponentially. This being said, when one does long distance running, they may burn more calories in the moment. But over the next 24 hours, the amount of calories burnt by the HIIT training is shockingly higher. Due to this, the amount of fat metabolised by long distance training is insignificant in comparison to HIIT.

Common sense perspective

   Let’s look at the extremes and elites of long distance training vs high intensity. Marathon runners are at one end of this spectrum with events lasting a little over 2 hours, on the other side of the coin, we have sprinters with the longest events lasting less than 45 seconds. How these athletes train is similarly different when considering the intensity and the volume. When one looks at both of these athletes they would both be considered as lean, but the sprinters body has significant higher lean body mass even though they use significantly less calories during the event. We can look at tons of this anecdotal evidence that surrounds us in the sporting world, but instead of doing that, lets poor ourselves into the research.


In 1990, Tremblay et al., demonstrated in their study for a given level of energy expenditure, individuals engaging in vigorous activities are leaner than those participating in less intense activities. To expand upon these findings, they wrote a second study that compared the effect of a 20-week low-to moderate-intensity continuous training (LMICT) program upon body fatness and muscle metabolism with a 15-week HIIT program. Despite the fact that the energy expenditure of exercise was twice as high in the LMICT (with a mean estimated energy cost of 120.4 MJ) as in the HIIT program (with a mean estimated energy cost of 57.9 MJ), there was a more pronounced reduction in subcutaneous fat (measured as the sum of six skin folds) with the HIIT program compared with the LMICT program. When the difference in the total energy cost of the two training programs was taken into account, the reduction induced by the HIIT program was actually nine-fold greater than the LMICT program. Muscle biopsies were also taken before and after the training programs to examine the effect of the two training programs upon muscle metabolism. It was shown that the HIIT program significantly increased the activity of an enzyme (3-hydroxyacyl coenzyme A dehydrogenase [HADH]) of the β-oxidation pathway (fat metabolism), whereas, the LMICT did not. This greater increase in lipid utilization is attributed to a greater increase in the post-exercise period since it is well established that excess post-exercise oxygen consumption (EPOC) is influenced more by the intensity of exercise rather than the duration. This study demonstrates that the amount of energy expended during the exercise is not as important as the overall energy expenditure. Further, vigorous activity produced greater metabolic adaptation in muscle tissue and favoured lipid oxidation in comparison to LMIT. These findings have been demonstrated and supported in numerous other studies. On top of this, it has been found that only during high intensity exercise is triglyceride within the muscle hydrolyzed to release acids for further direct oxidation. In LMICT research has disagreed on its effectiveness greatly, however, it is generally accepted that beginners may have some moderate early success when it comes to fat loss but quickly hit a plateau.

Tremblay et al. 1994 looked at the effects of endurance training vs high intensity intermittent training. Two separate training groups were evaluated. One group maintained an endurance training program for 20 weeks. The other group trained with HIIT for 15 weeks. The results showed that the HIIT group lost significantly more body fat. This is very interesting because the HIIT group trained for 5 weeks less and the endurance group had experienced greater caloric expenditure per workout (during the course of the workout). Based on the fact that the endurance group was burning more calories per session, yet lost less body fat, it becomes clear that the contributing factors for fat loss occurred after the training session. The after effect of more intense work makes this style of training the ultimate fat loss protocol.
High intensity training is an effective way of losing weight and improving anaerobic power. HIIT may not burn more calories during the training session, but over the following 24 hours it burns significantly more. On top of this, HIT training preserves muscle mass, strength, and power output. On the other hand, continuous aerobic training reduces power, produces slower athletes, and requires more time. Which training form do you think is best for you? In my opinion HIIT is the clear winner.

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