Measuring Exercise Intensity

There are several ways to measure your exercise intensity: target heart-rate checks, perceived exertion and talk test, and heart rate monitors, now increasing in popularity due to ease of use and relative accuracy.

For many years, measuring exercise intensity using the target heart-rate method and pulse check was the standard in group fitness and exercise videos. In more recent years, the easily-applied perceived exertion check and talk test has become more prevalent in both.

Today, heart rate monitors are becoming the new standard for goal-oriented and serious-minded exercise enthusiasts. Not only do they provide immediate and fairly accurate feedback but they can also track your progress and improvements in fitness over time.

The Target Heart Rate Method

The "Target Heart-Rate" is the level at which it is recommended to be working in order to challenge the cardio-respiratory system and to be working in the "training" or "aerobic" zone. Within this zone, your body burns a higher percentage of fat calories, therefore it is commonly referred to as the "fat burning zone". (However, research has shown that higher intensity training results in an increased overall caloric burn - see intensity training.)

If you are just getting started with cardiovascular exercise, it's a good to know your "normal" or beginning heart rate, which will help you monitor your overall gains in your cardiovascular fitness.

Prior to your exercise session, first check your normal activity heart-rate. After you have gradually increased the level of intensity in your work effort, you should check to see where you are working within your training zone. At the peak of your intensity effort, measure your heart rate, then as you decrease intensity back to normal, check your heart rate again. The amount of time from peak activity back to normal heart rate is your recovery time. By measuring how long it takes for you to recover will give you an idea of your improvement in cardiovascular fitness. The fitter you are, the faster your heart-rate will recover back to normal.

Calculating Target Heart Rate

The most prominent and accurate means of determining target heart-rate is the Karvonen formula. This formula calculates a percentage of the heart-rate reserve, which is the difference between the resting heart-rate and the maximal heart-rate.

Heart-rate reserve = maximal heart-rate - resting heart-rate

Maximal Heart-rate is the highest rate a person can attain during exercise. While an electrocardiogram test would provide the most accurate MHR, for practical application an age-predicted heart-rate formula was developed.

Maximal heart-rate = 220 - age

This formula is based on the assumption that one's heart rate at birth is 220 and decreases by one every year. The accuracy of determining maximal heart-rate based on this formula can vary at any given age by + 10 beats per minute.

Resting Heart-rate is the rate at which your heart beats at full rest. It is recommended that this rate be taken before getting out of bed, counting the pulse for a full 60 seconds, 3 mornings in a row and averaging the counts.

Determining the target heart-rate ranges:

Karvonen Formula

Using the Karvonen formula, the generally accepted heart-rate ranges are between 60% to 80% of maximal heart-rate reserve.

Target heart-rate = % intensity X heart-rate reserve + resting heart-rate

Here's how it would be calculated for a 45 year old with a resting heart-rate of 80 and an age-predicted maximal heart-rate of 175 at an 80% intensity level of maximum heart-rate reserve:

175 (age predicted MHR)
- 80 (resting heart-rate)
95 (heart rate reserve)
X.80 (intensity level)
76.00
+80.00 (resting heart-rate)
156.00 (target heart rate)

It is recommended that the formula be applied to both ends of the range, 60% and 80%, to determine the target heart-rate training zone.

The Karvonen formula is considered more accurate than the Maximal heart-rate formula, because the resting heart-rate is used in the calculation. From a practical standpoint, few people actually figure out an average for their true resting heart-rate.

Maximal Heart-Rate Formula

Therefore the simplified Maximal heart-rate formula is the standard that was used in most group exercise settings:

target heart-rate = maximal heart-rate (mhr) X % intensity

For the same 45 year old, here's how the range would be figured:

At 60 % Intensity -

175 (mhr: 220 - age)
X.60 (percent intensity)
105 (target Heart-rate)

At 80% Intensity -

175 (mhr: 220 - age)
X.80 (percent intensity)
140 (target heart-rate)

In group fitness settings, easy reference for intensity levels may be provided with a Target Heart Rate Chart. To view a sample of a heart-rate/age/intensity chart, click here.

Next - The Pulse Check - checking your heart rate during exercise .