Wednesday, April 23, 2008

How much calories can you burn?

One of the most popular questions that people like to ask when joining a fitness class is how much calories can the class help them to burn. Honestly speaking, although I would love to answer that question, I really can’t tell it off hand.

All of us are different individuals. We are different in terms of genetics, gender, age, height, weight, body fat, fitness level, metabolism rate, health condition, muscle mass, daily diet, to name just a few. If I tell you that you can burn X amount of calories after joining the class, I am just not painting you the whole picture. Unless you and I share all the same statistics, given the same period of workout time, we don’t burn the same amount of calories.

On the other hand, instead of knowing how much calories can the class help us to burn, maybe we should look into how much calories do we want to burn during our workout. The fact is, the harder we work, the more calories we burn. The question now is, how hard is hard?

To work harder is to work at higher intensity level. And one of the best indicators to know of the intensity level is by referring to our heart rate during the workout duration: More calories are expended, or burnt, at higher heart rate. The following table shows my personal average energy, or calories, expended at different heart rate zones:

My Current Energy Expenditure Table

Let say, for instance, I maintain my heart rate at 50-60% of my maximum during my workout. After one hour of exercise, I can burn about 499 Calories. If I raise my heart rate up to 70-80% of my maximum, then I can burn around 849 Calories for that hour. As you can deduce from the table above, at higher heart rate zone (HR zone), more calories are expended or burnt.

The bottom line is, if we want to burn more calories, we simply need to work at higher intensity level, or at higher HR zone. If we don't want to work too hard but still want to burn that much of calories, what we need to do then is to work for longer period of time. That is, in order to burn about 1,000 Calories, I need to exercise for nearly 2 hours while maintaining my heart rate at the 50-60% HR zone. If I want to burn the same amount of Calories within an hour, I’ll have to work myself harder at the 80-90% HR zone. Alternatively, I can also switch from one HR zone to another from time to time and make up the desired total energy expenditure. For example, I can workout in the 60-70% HR zone for an hour, and 23 minutes in the 70-80% HR zone. So, 674+[849*(23/60)]=999 kcal.


This Energy Expenditure table is that of my personal reference. It gives me an idea of how much energy, or calories, I’ll expend at each training intensity (in both kcal/min and kcal/hour). From there, I get to know how much to eat (energy intake) before/after the exercise session and find out my personal exercise intensities in HR%. The data in this table changes when I change my weight (in kg), HRmax (maximum heart rate, 220 minus current age) and VO2max values. The higher the weight, the more calories can be expended. The higher the HRmax (or the younger the age), the more calories can be expended, The higher the VO2max, the more calories can be expended too. Yours should be different from mine.

VO2max (also maximal oxygen consumption, maximal oxygen uptake or aerobic capacity) is the maximum capacity of an individual's body to transport and utilize oxygen during exercise, which reflects the physical fitness of the individual. Higher the value, fitter is the person.


jeandesign said...

Actually we should spend how many hours per week to exercise is good for health & help to burn our calories?

|| Eugene Lim || said...

Referring to the latest report with guidelines on physical activity, "Physical Activity and Public Health: Updated Recommendation for Adults From the American College of Sports Medicine and the American Heart Association" (click here to download the report in Adobe PDF file format, file size: 385 KB), originally published online on 1 August 2007, it states that:

"To promote and maintain health, all healthy adults aged 18-65 years need moderate-intensity aerobic physical activity for a minimum of 30 minutes on five days each week, or vigorous-intensity aerobic activity for a minimum of 20 minutes on three days each week."

As you can see, this is the minimum guideline if we are "all healthy" and our purpose is to "promote and maintain health." If we are more ambitious, as to lose more fat, to have better stamina, to improve cardio vascular system, and so on, we will have to work more than this recommendation.

There is no fixed rules as to how long should we work out. All of us have different purposes when we exercise. If our purpose is to lose fat, then we will have to burn more calories, this means we will have to either work at a much higher intensity during the workout, or to spend longer time in working out. On the other hand, if we have achieved what we want and merely want to maintain it, then perhaps we can stick to the guideline recommended by ACSM/AHA above.

serra said...

how about bodyCombat? how much calories can be burned in an hour of bodyCombat class?

|| Eugene Lim || said...

Hi serra,

Glad to see you here again. Your question had actually been highlighted and "answered" in paragraphs 1 and 3 of this post How much calories can you burn?. Should you need more explanation, please drop by again. :-)