Heart rate is generally accepted as the gold standard for measuring intensity during aerobic activities, such as running, swimming, cycling and so on. The target heart rate (also called the training heart rate) is a percentage of the estimated maximum heart rate and it varies based on the age of the person doing the exercise. It is the range in which a person can achieve the greatest cardiovascular benefit from aerobic exercise without “overdoing” it. Target heart rate is measured in beats per minute (bpm).

There is a low and a high range of the target heart rate. The recommended target heart rate zone for moderate-intensity physical activity should be 50 to 70 percent of maximum heart rate. Examples of moderate-intensity activities are walking briskly, pulling or carrying golf clubs, recreational swimming, pushing a powered lawn mower, playing tennis doubles, riding a bike 5 to 9 mph with few hills, washing and scrubbing the floors and weight lifting. This level of activity burns approximately 3.5 to 7 kcal per minute.

The generally accepted target heart rate zone for vigorous-intensity physical activity is considered to be 70 to 85 percent of the maximum heart rate. Examples of vigorous-intensity activities are running, jogging, race walking, swimming laps, pushing a hand-powered lawn mower, tennis singles, biking more than 10 mph or with steep hills, moving furniture and circuit training. This level of activity burns approximately 7 or more kcal per minute.

Simple math shows that equal amount of calories can be burned in less time with vigorous-intensity activities compared with lower-intensity activities. Staying within these parameters means a person is exercising within the desired target heart rate zone. Following the steps described below will help determine a person's maximum heart rate as well as his or her target heart rate zone during aerobic exercise.

• First, find the maximum heart rate. Maximum heart rate (MHR) = 220 – age. For example, the MHR of a 50-year-old would be 170 beats per minute (bpm).
  
  
• Multiply the MHR by 0.7 to get the low range of the target heart rate zone. For example, the low range for a 50-year-old is 119 bpm (170 x 0.7).
  
  
• Multiply the MHR by 0.85 to get the high range. For example, a 50-year-old should not exceed a heart rate of 145 bpm (170 x 0.85).

To achieve cardiovascular benefits, a person should exercise for at least 20 minutes within his or her target heart rate zone. This is most efficiently done by using an electronic heart-rate monitor, which may be embedded in an exercise machine or worn separately by the exerciser.

If an electronic heart rate monitor is not available, a person can manually check his or her own heart rate by monitoring the radial pulse of one arm with the third and fourth fingers of the opposite arm. The radial pulse can be found by following the following steps:

• Position one hand with the palm facing up toward the ceiling.
  
  
• The pulse of the radial artery can be felt on the palm side of the wrist just below the base of the thumb. Get comfortable finding this pulse before beginning exercise so it is easy to find quickly while performing an activity.
  
  
• Use the pads of the third and fourth fingers of one hand to feel the radial pulse of the opposite arm. This is important because the thumb and index finger have their own pulses, which can cause a miscount of the actual beats per minute.
  
  
• When the radial pulse is found, use a clock with a second hand or a timer and begin counting beats. The first beat should be counted as “0” and the count should proceed from there (0...1...2...etc.).
  
  
• Count the number of beats felt during a one-minute period of time. For a faster but slightly less accurate alternative, count the number of beats felt in 30 seconds and multiply that number times two, or count the number of beats felt in six seconds and multiply that number times 10 to estimate your heart rate.
  
  
• Try to keep moving by marching in place while counting the pulse rate.
  
  
• People unable to find their radial pulse can use the carotid pulse on the side of the neck located just below the angle of the lower jaw.
  
  
• Apply only light pressure over the wrist or neck with the third and fourth fingers. Too much pressure over the pulse can lead to a miscount.

The maximum heart rate is a number used to help calculate the  target heart rate zone. People should avoid reaching their maximum heart rate during aerobic exercise, nor should they exercise above 85 percent of this number.