1. METS

A MET is a multiple of resting oxygen consumption (or functional capacity) which is approximately 3.5 milliliters of oxygen per kilogram of bodyweight per minute. The intensity of exercise can be expressed as a specific percentage (for example 60-90%) of a person's maximal oxygen consumption. The idea is to select activities that are known to require energy expenditures at a desired level.

For example, if an individual has a functional capacity of 10 METS and desires to reach an intensity level of 60%, then the intensity required would be 60% of 10 METS which equals 6 METS.

Due to the fact that standardized tables have been developed for certain activities with regards to energy expenditures expressed in METS, this system can be very effective for those individuals who need strict supervision in their exercise programs. People can select specific activities such as canoeing or skiing and determine the related exercise intensity.

2. Intensity by Percentage of Maximal Heart Rate

Maximal heart rate can be calculated by a maximal functional capacity test using a bicycle or treadmill ergometer or by age-predicted maximal heart rate tables. These tables often employ the 220-age equation for determining maximal heart rate. This method applies the following formula:

Training Heart Rate Range = Maximal measured or predicted heart rate x 60-75% x 1.15

As an example: A 50-year-old man for whom an intensity of 60-75% of maximal heart rate is desired:

170 (age-determined maximal heart rate, 220 - age) x .60 (60% low intensity range) 102 (60% lower limit exercise heart rate)

170 (age-determined maximal heart rate, 220 - age) x .75 (75% upper intensity range) 128 (75% upper limit exercise heart rate)

Or a target heart rate of 102 - 128 beats per minute x 1.15 = 117 - 147 beats per minute.

3. Intensity by the Karvonen Formula

The Karvonen Formula is very much like the percentage of maximal heart rate method, but resting heart rate is taken into account. This formula can also be referred to as the heart rate maximum reserve method. Here is the formula:

Training Heart Rate = Maximum heart rate - Resting heart rate x Desired Intensity (50-85%) + Resting heart rate

For example, to calculate the target heart rate for a 40-year-old person with a resting heart rate of 80 beats per minute at an intensity level of 70%:

220 - 40 = 180 (predicted maximal heart rate) - 80 (Resting heart rate) 100 (Heart rate reserve) x .70 (70% intensity) 70 + 80 (Resting heart rate) 150 (Target heart rate at 70% of heart rate reserve)

4. Intensity by Perceived Exertion

Assigning a numerical value from 6 - 20 of perceived (and therefore subjective) feelings of exertion is another method of measuring intensity. This is sometimes called the Borg Scale because it was originally developed by Dr. Gunnar Borg. This method takes into consideration an exerciser's perceptions of exercise fatigue, including psychological, musculoskeletal, and environmental factors.

The ratings of perceived exertion (RPE) are assigned a number from the Borg Scale with 6-7 being extremely light and 19-20 being very hard. Thus, an RPE of 12-13 would correspond to approximately 60-79% of maximal heart rate or 50-74% of maximal oxygen consumption or heart rate maximum reserve.

The Borg Scale starts at 6 to correlate with exercise heart rates. For example, an RPE of 6 would approximate a heart rate of 60 and an RPE of 15 would approximate a heart rate of 150. This scale has recently been revised with a 0-10 rating scale that is somewhat easier to use.

5. Intensity by the Talk-Test Method

This is also a subjective test and it is very useful in determining the comfort zone of aerobic exercise intensity. Individuals should be able to maintain comfortable and rhythmic breathing patterns during all phases of a workout session to ensure safety. This is an especially effective technique for beginners, but advanced trainees who progress to higher intensity levels may find this method too conservative.