Intervals for Cardio


Target Heart Rate Zone

The target heart rate zone (THRZ) is a range of heart rate percentages that a person aims for when exercising.  The range is expressed as a percentage of your maximum heart hate (Max HR).  Your Max HR is defined as the maximum amount of times your heart can beat per minute.  The American Heart Association recommends exercising within 50%-85% of your Max HR.  While the AHA provides a good guideline to follow, experienced and suitably fit people can train up to and above 90% of Max HR.

How to find your Target Heart Rate Zone

  First determine your Max HR

I will cover both the standard and updated formula for calculating Max HR.  Either method is good to use but the latter is said to be more accurate.

The standard way to calculate Max HR is simply 220 minus your age.
So if you are 30 years old your Max HR is 190.

Solution: 220 - 30 = 190 Max HR

A new and more accurate formula for Max HR was published by the Medicine & Science in Sports & Exercise journal. The updated formula for Max HR is 206.9 - (0.67 x age).  So if you are 30 years of age your Max HR is 187.

Solution: 206.9 - (0.67 x 30) = 187 Max HR

  Then Calculate your THRZ

To find your THRZ simply take 50%-85% of your Max HR.
So if you are 30 years old and your Max HR is 187 your THRZ is 94-159 beats per minute.


.50 X 187 = 94 beats/minute
.85 X 187 = 159 beats/minute

If you want a more personalized and accurate THRZ you can opt to use the Karvonen Formula.

The Five Target Zones

The THRZ can be broken down into 5 separate zones, which all burn fat, improve fitness, and provide health benefits.  The body will burn a higher percentage of fat calories at lower intensities but at higher intensities you'll burn more total calories.  Keep in mind that total calorie expenditure is more crucial than the percentage breakdown of fat and carb calories.  The more total calories burned, the more weight you'll lose.  Yes, it's that simple.

As the zones get higher...

Exercise intensity increases
More calories are burned per minute during exercise
More calories and fat are burned after exercise
More calories and fat are burned around the clock
Your fitness level increases

 Target Zones  Percentage of Max HR  Exercise Intensity
 Z1 Healthy Heart  50% - 60%  Very light to light
 Z2 Temperate  60% - 70%  Light to moderate
 Z3 Aerobic  70% - 80%  Moderately hard
 Z4 Anaerobic  80% - 90%  Hard
 Z5 Red Line  90% - 100%  Very hard

Healthy Heart Zone (50% - 60% of Max HR)
The lowest level you can exercise in and still increase your fitness.  Suited for beginners or people who have stopped exercising regularly and lost their conditioning.  This zone can be used for just improving your overall health.  It can also be a good recovery zone for people who are over-trained and need to take a break.

Temperate Zone (60% - 70% of Max HR)
This is the zone where the heart begins to benefit.  Training in this zone will begin improve your heart's ability to pump blood and improve the muscle cells ability to use oxygen.  This zone is good for long slow endurance exercise as the body becomes more efficient at feeding the working muscles more efficiently. In this zone stored body fat is the primary source of energy utilized hence this zone is referred to as the weight management zone.

Aerobic Zone (70% - 80% of Max HR)
This zone is the most effective for overall cardiovascular fitness.  This is the best zone to workout in to increase your cardio-respiratory capacity, which is the body's ability to transport oxygenated blood to the muscle cells and carbon dioxide away from the cells. After a while you will be able to cover more distance during workouts in less time.  This zone is also effective for increasing overall muscle strength.

Anaerobic Zone (80% - 90% of Max HR | 85%-90% = Anaerobic Threshold)
This level is where you cross over from aerobic to anaerobic training which is called the anaerobic threshold.  This is the point where the body cannot effectively remove lactic acid from the working muscles quickly enough.  This zone is mainly for people who want to increase their performance levels. You would characterize this zone as hard.  During exercise in this zone your muscles burn, your breathing is heavy, and you become fatigued quickly.  The benefit of training in this zone is that you can increase your body's ability to tolerate and deal with lactic acid for a longer period of time as the enzymes in your muscles responsible for anaerobic metabolism are increased.  For sport competitors it is good to become accustomed to your anaerobic threshold as many fit athletes can compete at or above their anaerobic threshold.

Red Line Zone (90% - 100% of Max HR) 
You will only be able to train in this zone for short periods of time.  You should not train in this zone unless you are very fit.  In this zone lactic acid builds up very quickly as your muscles are operating with oxygen debt.  The benefit of training in this zone is that you can increase your fast twitch muscle fibers which increase speed.  You will not be able to stay at this intensity level very long so short work intervals should be used when training in this zone.