Quick and intense or long and slow?

Low vs High Intensity Exercise

A few years ago, you may remember many fitness professionals prescribing lower intensity activity to maximize fat loss.  Many fit people lowered the intensity of their workouts fearful that they were not burning fat.  Unfortunately, they were misled and many people still believe that low intensity activity is the best way to maximize fat loss.  The reality is that the activity that expends the most amount of calories will lead to the most amount of fat burned.

Yes, during lower intensity activity you will burn a higher percentage of fat and during higher intensity activity you will burn a higher percentage of carbohydrates or sugars.  But the important point to note is that during low intensity activity you are burning fat at a higher percentage of a lower amount of calories.  When you exercise at a lower intensity you are definitely expending less calories.  The selective use of fat as a fuel, specifically at lower intensities, does not translate into greater fat loss, regardless of how tempting it is to draw this conclusion.  The more important focus with regard to calories expended, is not the percentage of energy coming from fat, but rather the total volume of fat used and the total number of calories expended.  Let’s look at the math.   

At 60% max heart rate (easier intensity)

·      Approximately 50% of calories come from fat (50% from sugars)

·      Approximately 8 kcal/min are expended

·      60 minutes x 8 kcal/min = 480 total calories

·      50% x 480 kcal = 240 fat calories

At 80% max heart rate (more vigorous intensity)

·      Approximately 40% of calories come from fat (60% from sugars)

·      Approximately 11 kcal/min are expended

·      60 minutes x 11 kcal/min = 660 total calories

·      40% x 660 kcal = 264 fat calories

From these figures you can see how fitness leaders could have been misled.  If you were to examine only the first line, the percentage of fat being burned as fuel, you would definitely prescribe lower intensity activity.  However, if you examine the whole picture, it is clear that higher intensity activity definitely expends more calories and also more fat.  Here are some more statistics to convince you.

It takes approximately 3,500 calories to burn one pound of fat.  Compare the following exercise programs. 

Program A – Easier intensity (approximately 5kcal/min) – For example, easy walking

·      30 minutes of activity 3x/week

·      150kcal/session x 3x/week

·      450kcal/week

·      It would take 8 weeks to burn 1 pound of fat

Program B – Same intensity as above but for a longer duration

·      60 minutes of activity 3x/week

·      300kcal/session x 3x/week

·      900 kcal expended per week

·      It would take 4 weeks to burn 1 pound of fat

Program C – More vigorous intensity (approximately 10 kcal/min) – For example, jogging or power walking up and down hills

·      60 minutes of activity 3x/week

·      600kcal/session x 3x/week

·      1800 kcal expended per week

·      It would take 2 weeks to burn 1 pound of fat

If you followed Program A, it would take you eight weeks to burn one pound of fat!  Most people would give up by then!  If you could easily handle the higher intensity of Program C, wouldn't you prefer to just wait 2 weeks to burn off that pound of fat deposited around your waist, hips or thighs?  Remember though, if you can't handle the higher intensity of Program C, follow Program B, which means you can maintain the easier intensity but you just have to go longer. 

Time is definitely an issue for a lot of exercisers and most don't want to spend hours in the gym if they can get the same results in a shorter period of time. 

So, the bottom line is that if you want to maximize fat loss, you need to maximize the number of calories you expend.  An exercise physiologist's rule for fat loss is "Go as hard as you can, as long as you can, as often as you can!"  This type of prescription will definitely maximize fat loss; however, is generally not the safest route to take.

If you did follow this prescription, each training session may be so difficult that you dread each of your workouts and may have a difficult time adhering to your program.  You may find yourself skipping workouts, which of course will get you nowhere.  In addition, if you followed this prescription, you may also start to experience numerous injuries or illnesses because our body is not capable of going hard all the time.  So instead, the recommended fat loss prescription is one that includes all intensity training zones.  Sometimes you’ll go all out for shorter periods of time, and other times you’ll go for a longer duration with less intensity.