Creative Commons License photo credit: JasonGoodger

I have recently been involved in a discussion regarding the necessity of cardio for fat loss. By cardio I am referring to slow long distance aerobic exercise such as jogging for 30 minutes or longer. The personal opinions expressed in the discussion were just that. Opinion. One side of the debate suggesting that if we wish to posses the elusive six-pack long slow boring cardio is necessary. The other side was not convinced. Others and myself suggested that high intensity but short duration interval work was as effective if not more so then traditional cardio.


I don’t like to make decisions regarding what is the best use of my time nor what is best for my health based upon pure anecdotal evidence. So I thought I would share what I know of the scientific research into this matter. That way you can inform yourself and make up your own mind. Please stick with me while I detail the science. I promise it will be worth your time investment. And if you can’t, then well, I think there is a TV somewhere you should be watching.

Angelo Tremblay, Ph.D., is a researcher at the Physical Activities Sciences Laboratory, Laval University, Quebec, Canada. Tremblay divided 27 inactive, healthy, non-obese adults (13 men, 14 women, 18 to 32 years old) into two groups. The first group was subjected to a 20-week cycling endurance-training program of 30 to 45 minutes sessions, 4 or 5 times a week. The intensity level began at 60% of heart rate reserve and progressed to 85%, which is more intense than usually prescribed for weight or fat loss.

The second group did a 15-week program of mainly high-intensity-interval (HIT) training. To begin with, because the participants were not accustomed to exercise, they started with 30-minute sessions of continuous exercise at 70% of their maximum heart rate. Then the group quickly progressed to 10 to 15 bouts of short (15 seconds progressing to 30 seconds) or 4 to 5 long (60 seconds progressing to 90 seconds) intervals separated by recovery periods allowing the heart rate to return to 120-130 beats per minute. The intensity of the short intervals was initially fixed at 60% of the maximal work output in 10 seconds, and that of the long bouts corresponded to 70% of the individual maximum work output in 90 seconds. Intensity on both was increased 5% every three weeks.

The researchers calculated that the group doing long slow distance exercise burned more than twice as many calories while exercising than the group doing high intensity intervals. However, skinfold measurements showed that the HIT group lost more subcutaneous fat. Even more interesting was the fact that when the difference in the total energy cost of the program was taken into account the subcutaneous fat loss was ninefold greater in the HIIT program than in the traditional long slow distance cardio program. What this means is the HIIT group got nine times more fat-loss benefit for every calorie burned exercising.

To examine how this could be possible the researchers took muscle biopsies and measured muscle enzyme activity to determine why high-intensity exercise produced so much more fat loss. What they found was compared to endurance exercise high-intensity intermittent exercise causes more calories and fat to be burned following the workout.

There is an important cravat to this information. Interval work can be extremely taxing. You should always start an interval program slowly, particularly if this is your first experience with such a program. Always take it slower then you feel you can go. High intensity interval training is not for beginners. If you have health problems or are overweight and not used to exercise you do need to build a traditional aerobic cardio base first. However, sticking religiously to the same long slow distance program flies in the face of scientific evidence. Once you have your aerobic base it is time to make the step up to interval training.

Further, there is a very real pitfall you should be aware of with high intensity interval training. Quite simply “high intensity” means different things to different people. When I perform high intensity interval training with a kettlebell (you can read about my workouts in my article: Kettlebells and a Workout to Die From) I generally want to die more then I want to do another interval of activity well before my 12-minute workout is over.

HIT is physically and psychologically taxing. Dr Tabata wondered how many people would “feel eager to do this type of exercise.” This is because the protocol was invented to stress the cardiovascular systems of top Japanese speed skaters who achieved medal positions in the Olympic games. I can’t help feeling that those who have supposedly tried HIT and did not get fat-loss results were missing the high-intensity part and simply doing interval training.

I will leave you with one final thought. Take a look at the wasted bodies of athletes who are long distance runners and compare them to the strong healthy bodies of sprinters. Who’s body would you rather have?

If you are interested in getting into kettlebells for some real HIT sessions you might like to check out to my kettlebell buyer’s guide for kettlebell beginners.

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