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The Princeton Longevity Center Medical News

Intensity Matters Most!

By Chris Volgraf, CSCS

With nearly 2 out of 3 Americans being overweight or obese, two thirds of our country needs to lose weight.  Everyone is looking for the newest weight loss diet, the magic pill or the newest exercise to shrink themselves back into acceptable weight and better shape. When it comes to exercise, the vast majority of America is confused or simply mislead on what they need to do to bring about optimal weight loss. 

The “Fat Burning Zone” or low intensity cardiovascular exercise (50%-65% HRmax) has long been touted as the most efficient way to burn calories from fat.  Besides, science has shown us that we burn the highest percentage of our calories from fat at low intensities of exercise. So the logical choice for exercise intensity for peak weight loss is low intensity right? WRONG!! 

High intensity cardiovascular exercise (70%-90% HRmax) burns more calories from fat, and more importantly, total calories. Another consideration is the effect that exercise has on energy expenditure after exercise. Following a high intensity exercise bout, the rate of metabolism is elevated for a slightly longer period of time (when compared to a lower exercise bout), and more energy is expended as your body returns to resting condition. With regular aerobic exercise, this post-exercise energy expenditure will positively contribute to weight loss goals. As if that were not enough, high intensity cardio exercise also offers better improvements in cardiovascular, respiratory and nervous system health and function.

It is really just a numbers game that merits a closer look.  During low intensity exercise, approximately 50% of the calories burned come from fat. As exercise intensity increases, the percent of energy derived from fat decreases. However, the absolute amount of energy derived from fat is actually increased! As exercise intensity increases, so does total energy expenditure (caloric expenditure). Even though a smaller percentage of the energy expenditure is coming from fat (roughly 40%), more calories from fat are burned because there is greater absolute energy expenditure. Therefore, expressing energy derived from fat as a percentage of energy expenditure without considering the total energy expenditure is misleading.  Here is a table that will help clear things up.


Low Intensity
50% of VO2 max or
approx 60-65% MHR

High Intensity
70% of V02 max or
approx 80-85% MHR

Total calories expended per min.



Fat calories expended per min



Total calories expended in 30 min.



Total fat calories expended in 30 min.



Percentage of fat calories burned



                                                                                    *courtesy of APEX Fitness Group

Now before you go running on the treadmill at 8 mph or training on the elliptical trainer at 200 strides per minute, high intensity exercise is not for everybody.  Low intensity cardiovascular exercise is still recommended for beginner and novice exercises as the preferred intensity of exercise.  It takes a good level of fitness to handle more intense exercise due to the risk of cardiac complications and orthopedic injury.  Therefore it is very important to receive physician’s clearance and a fitness assessment prior to starting with a fitness program. 
The preferred way to introduce high intensity cardiovascular exercise into your routine once you have reached a good baseline level of fitness is to begin adding timed higher intensity intervals into your cardio sessions.  “Interval Training” mixes timed intervals of low to moderate exercise with high intensity exercise (near max output) to allow for recovery between every high intensity interval. A high intensity interval could be as short as 20-30 seconds or as long as 3-5 minutes.  The low to moderate intervals should be equal to or slightly longer than the high intensity interval to allow for recovery. This will help you ease into high intensity exercise without the risk of overtraining or overuse injuries. The duration of each session can be a little as 10-15 min and as long as 30 min.   

Even when one has reached an excellent fitness level, you still want to allow for recovery.  Mixing lower intensity steady state sessions with high intensity (with 1 or more days between interval sessions) is necessary to allow for “active recovery.”  The general public should only perform interval training twice a week, but they may perform high intensity steady state exercise (70-90% HRmax) up to 5 sessions a week as long as the intensity level is closer to 70-80% max heart rate.
As you can see, high intensity exercise is the most effective way to increase your aerobic fitness conditioning, burn calories and lose weight.  Scheduling sessions properly during the week to allow for recovery will allow high intensity exercise to have a place in your program for years to come.

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