Measuring Physical Activity Intensity



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The intensity of physical activity, or how hard your body is working, is typically categorized as light, moderate, or vigorous based on the amount of energy or effort a person expends in performing the activity.

Talk Test

The talk test method of measuring intensity is simple. A person who is running at a light intensity level should be able to sing while running. One who is running at a moderate intensity level should be able to carry on a conversation comfortably while engaging in the activity.
If a person becomes winded or too out of breath to carry on a conversation, the activity can be considered vigorous.

Target Heart Rate and Estimated Maximum Heart Rate

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A second way of monitoring running intensity is to determine whether a person's pulse or heart rate is within the target zone during physical activity.

For moderate-intensity running, a person's target heart rate should be 50 to 70% of his or her maximum heart rate. This maximum rate is based on the person's age. An estimate of a person's maximum age-related heart rate can be obtained by subtracting the person's age from 220. For example, for a 50-year-old person, the estimated maximum age-related heart rate would be calculated as 220 - 50 years = 170 beats per minute (bpm). The 50% and 70% levels would be:

50% level: 170 x 0.50 = 85 bpm, and
70% level: 170 x 0.70 = 119 bpm
Thus, moderate-intensity running for a 50-year-old person will require that the heart rate remains between 85 and 119 bpm during physical activity.

For vigorous-intensity running, a person's target heart rate should be 70 to 85% of his or her maximum heart rate. To calculate this range, follow the same formula as used above, except change "50 and 70%" to "70 and 85%". For example, for a 35-year-old person, the estimated maximum age-related heart rate would be calculated as 220 - 35 years = 185 beats per minute (bpm). The 70% and 85% levels would be:

70% level: 185 x 0.70 = 130 bpm, and
85% level: 185 x 0.85 = 157 bpm
Thus, vigorous-intensity running for a 35-year-old person will require that the heart rate remains between 130 and 157 bpm during physical activity.

Taking Your Heart Rate

Generally, to determine whether you are running within the heart rate target zone, you must stop running briefly to take your pulse. You can take the pulse at the neck, the wrist, or the chest. It is recommend to use the wrist. You can feel the radial pulse on the artery of the wrist in line with the thumb. Place the tips of the index and middle fingers over the artery and press lightly. Do not use the thumb. Take a full 60-second count of the heartbeats, or take for 30 seconds and multiply by 2. Start the count on a beat, which is counted as "zero." If this number falls between 85 and 119 bpm in the case of the 50-year-old person, he or she is active within the target range for moderate-intensity running.

Perceived Exertion (Borg Rating of Perceived Exertion Scale)

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A third method of determining physical activity intensity is the Borg Rating of Perceived Exertion (RPE). Perceived exertion is how hard you feel like your body is working. It is based on the physical sensations a person experiences during running, including increased heart rate, increased respiration or breathing rate, increased sweating, and muscle fatigue. Although this is a subjective measure, a person's exertion rating may provide a fairly good estimate of the actual heart rate during physical activity* (Borg, 1998).

Practitioners generally agree that perceived exertion ratings between 12 to 14 on the Borg Scale suggests that physical activity is being performed at a moderate level of intensity. During running, use the Borg Scale to assign numbers to how you feel. Self-monitoring how hard your body is working can help you adjust the intensity of running by speeding up or slowing down your movements.

Through experience of monitoring how your body feels, it will become easier to know when to adjust your intensity. For example, a walker who wants to engage in moderate-intensity activity would aim for a Borg Scale level of "somewhat hard" (12-14). If he describes his muscle fatigue and breathing as "very light" (9 on the Borg Scale) he would want to increase his intensity. On the other hand, if he felt his exertion was "extremely hard" (19 on the Borg Scale) he would need to slow down his movements to achieve the moderate-intensity range.

*A high correlation exists between a person's perceived exertion rating times 10 and the actual heart rate during physical activity; so a person's exertion rating may provide a fairly good estimate of the actual heart rate during activity (Borg, 1998). For example, if a person's rating of perceived exertion (RPE) is 12, then 12 x 10 = 120; so the heart rate should be approximately 120 beats per minute. Note that this calculation is only an approximation of heart rate, and the actual heart rate can vary quite a bit depending on age and physical condition. The Borg Rating of Perceived Exertion is also the preferred method to assess intensity among those individuals who take medications that affect heart rate or pulse.

Metabolic Equivalent (MET) Level

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A fourth way of measuring physical activity intensity is by the metabolic equivalent, or MET, level. Although the intensity of certain activities is commonly characterized as light, moderate, or vigorous, many activities can be classified in any one or all three categories simply on the basis of the level of personal effort involved in carrying out the activity (i.e., how hard one is working to do the activity). For example, one can run at intensities ranging from very light to very vigorous.

1 MET = the energy (oxygen) used by the body as you sit quietly, perhaps while talking on the phone or reading a book.

The harder your body works during the activity, the higher the MET. Any activity that burns 3 to 6 METs is considered moderate-intensity physical activity. Any activity that burns > 6 METs is considered vigorous-intensity physical activity.