Fitness Goals

How Hard Should I Be Working During My Cardio Sessions?

Target Heart Rate/ Fat Burning Zone

Cardiorespiratory exercise (running, jumping, stepping, spinning aerobic class) is a good way to improve our aerobic capacity. As our aerobic strength increases, the efficiency at which we’re using oxygen increases, and we’re able to sustain longer activity. People often work out on cardio equipment but fail to make progress either in their weight loss or in their endurance or strength. There are many possible reasons for this. Most often, I find that it is because they are not working hard enough. Sometimes this is because they were led to believe that there’s some sort of fat burning zone which is way lower than their perceived maximum exertion—which is somewhat of a misconception…So how hard should you be working?

Some fitness professionals used to believe that if you worked out at a lower intensity you would be burning more fat. The idea was that your body requires less energy when you are working out at a lower intensity so the body would dip into fat stores rather than glucose (sugar)/blood sugar/sugar stored in your muscles for fuel. You may even still see target heart rate on some workout machines at gyms and find that this is targeting you to work out at 60-65% of your maximum heart rate…as if this is some sort of unique fat burning zone. Yes, it’s true that this is the aerobic training zone whose main source of fuel is carbs, fat and protein and where the anaerobic system mainly uses glucose for fuel. However, when you work out harder, and reach into the anaerobic zone, you burn more calories overall and therefore burn more fat calories and more sugar calories.

Take for instance, if you are working out at the gym for 30 minutes at your “target heart rate of 60%” and you burn 200 calories. For the point of illustration lets say 70% of those are from fat and 30% are from sugar. However if you spend the same30 minutes working at a higher intensity and burn like 300 calories, with 50% from fat and 50% is glucose..You are burning more calories from fat and more calories overall!

To further press the point, look at it this way: glucose that doesn’t get burned off can turn into fat anyway.

Another benefit of working in the anaerobic zone is the after-burn. What that means is that the body’s metabolism remains elevated longer after the workout. (Also known as excess post oxygen consumption).

Recovery of the metabolic rate after a cardio workout can be several minutes post-workout if you stay only in the aerobic zone, but after anaerobic training, it can be several hours and even up to 12 hours or longer for exhaustive interval training or circuit weight training. This post-exercise energy expenditure during the recovery can really speed weight loss.

OK, before you foolishly exert yourself into oblivion…just wait..and keep reading. I like to give clients a Target Heart Rate Range for establishing a safe and effective cardio training parameter. There are a few methods in which to do this but for today, I’m going to give you the simplest formula I know to get a good estimate.

(The drawback to this formula is that is underestimates Heart Rate Max for men and women under age 40 and overestimates it for men and women over 40..but knowing this, you can always fine-tune for your self). Here goes:

Target Heart Rate Formula:

Take 220 and subtract your age to get your age predicted maximal hart rate.

For instance:

220-40 years old= 180 This is the theoretical maximal heart rate of a 40 year old.

Then, multiply the result (in this case 180) by the percentage of maximum you would work at

I recommend keeping your heart rate between 64% and 94% of max. So the target heart rate range for this client would be between 115 and 169 beats per minute for safety sake.

Furthermore, I like to break it down for clients who are just starting out so they can progress safely or so that we can work in a class setting so as to monitor intensity for the warm-up, body of the workout and cool down. (Some folks push too hard in the warm up and cannot sustain that level during the bulk of the workout) this gives them a guideline.

The first zone for beginners would be 65-75% of maximum, the second zone 80-85%, and the third zone 86-90% of maximum

In the case of the 40 year old:

.65x 180= 117
So the first level is 117-135 Beats per minute

And so on….

.80x 180=
.85x 180=
For level 2

For level 3

Realistically, you cannot sustain 94% too long, and at 60% you’re not making too much impact on your cardio strength unless you are a beginner. For those unaccustomed to exercise, we may start out in zone 1 for 2 or even 3 weeks and adjust as necessary. Seasoned exercisers may want to strive for the 80%+ for the bulk of their workout. Those using High Intensity Interval Training (a topic for another post) may want to spike their workout with intervals in the 80-90% range occasionally. These guidelines are for healthy individuals. (The recent recommendations for pregnant women is not to exceed 140 beats per minute but please check with your healthcare provider for your individual situation…Those with CVD risk factors, or on blood pressure medication will have unusually low heart rate readings so the method discussed here may not apply. Again, please check with your healthcare provider.)

One great way to monitor how hard you are working that I highly recommend, is to wear a heart rate monitor. These are relatively inexpensive, easy to get (most sporting good stores have them) and allow you to know your heart rate at a glance.

You can also measure the number of beats in 10 second pulse check at the radial (wrist) artery or the carotid (neck) artery and then multiply by 6 to give you the approximate number of beats per minute..(10×6=60 seconds in a minute) (Please don’t stop moving while you are checking as this can cause blood to pool in your extremities and cause you to be keep moving or at least lifting your knees)

Another methods for monitoring intensity include the talk test and the rate of perceived exertion.

Now you know how hard you should be working during your cardio workouts. 220 – age x % of max (60-90% of max) you want to work in.


Fitness Theory and Practice : A Comprehensive Resource for Group Fitness Instructors.Aerobics and Fitness Association of America. Fifth Edition 2010. p. 254 -256

NASM Essentials of Personal Fitness Training Third Edition Ed. Miceal A. Clark, Scott C. Lucett, Rodney J. Corn 2008. p. 110


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