Maximum Heart Rate - February 23, 2010 Newsletter

Maximum Heart Rate

EHE Newsletter, Volume 10, Number 8
February 23, 2010

What is Maximum Heart Rate?

By monitoring heart rate, an individual can determine if he or she is exercising at an appropriate level. Maximum heart rate (MHR) is the number of times that an individual’s heart would beat within one minute if it was working at its maximum capacity; it is the upper limit of what the cardiovascular system can handle during physical activity. Although a number of formulas have been put forth to calculate MHR, the best known formula is the following:

MHR = 220 — Age

During exercise, the heart beats faster to meet the demand for more blood and oxygen by the muscles of the body. The more intense the activity, the faster the heart will beat. One way of monitoring physical activity intensity is to determine whether an individual’s pulse or heart rate is within the "target zone" during physical activity. According to The Centers for Disease Control and Prevention (CDC), during moderate–intensity physical activity, a person’s target heart rate should be 50 to 70 percent of his or her maximum heart rate. A healthy adult performing vigorous physical activity should aim for a target heart rate of 70 to 85 percent of his or her maximum heart rate.

How to Determine Heart Rate

In order to determine if an individual is exercising within his or her heart rate target zone, he or she should take a brief break from exercising and check his or her heart rate/pulse. A full 60–second pulse count can be taken, a 30 second count can be taken and multiplied by 2, or a 10 second count can be taken and multiplied by 6. The count should start on a beat, which is counted as "zero." If the pulse is below the target zone, it is recommended that the individual increases his or her rate of exercise. If the pulse is above the target zone, the individual should decrease his or her rate of exercise.

It is important to note that some medicines and medical conditions (specifically, heart disease, high blood pressure and diabetes) might affect an individual’s maximum heart rate. A healthcare professional should always be consulted in this regard. If there is concern, heart rate ranges for exercise should be prescribed by a doctor or an exercise specialist.

Are Maximum Heart Rate Formulas Accurate?

"MHR = 220 — Age," the formula commonly seen in medical textbooks and in health clubs across the United States, originated in the late 1960s. It was developed by Dr. William Haskell, a young physician in the United States Public Health Service and his mentor, Dr. Samuel Fox, who led the Service’s program on heart disease. They were trying to determine how strenuously heart disease patients could exercise. The formula was never intended as an absolute guide as it is often used now; it was meant only as a rough guideline. It is an excellent example of an idea that has become accepted as truth despite a lack of supporting scientific evidence. According to the May 2002 Journal of Exercise Physiology Online, the official journal of The American Society of Exercise Physiologists, research spanning more than two decades has revealed that, despite the acceptance of this formula, there are large errors inherent in this estimation of MHR. In fact, according to the Journal, there is no MHR estimation formula that provides an acceptable level of accuracy.

Individuals who are interested in more than an estimate of their MHRs should consider discussing their target ranges with an exercise physiologist or personal trainer. The only true way for a person to know his or her maximum heart rate is to have a maximal exercise tolerance test or stress test performed. For individuals who cannot have one of these tests done, the next best measure of exercise intensity is the "Rate of Perceived Exertion" or RPE.

Rate of Perceived Exertion

Since its development in the early 1960s, the Rate of Perceived Exertion Scale (RPE) has been embraced by clinicians, researchers and exercise enthusiasts as an inexpensive and simple technique for monitoring and adjusting exercise intensity. "Perceived exertion" refers to the intensity at which an individual feels his or her body is working. According to the CDC, it is based on the physical sensations that a person experiences during physical activity including increased heart rate, increased respiration or breathing rate, increased sweating and muscle fatigue. It is a subjective measure; it is believed, however, that an individual’s exertion rating may provide a fairly good estimate of the actual heart rate during physical activity.

The standard is the Borg Scale of Perceived Exertion. This 15–category scale for the rating of perceived exertion during physical activity has been widely researched for its use in both clinical and exercise settings. The scale ranges from a rating of 6 (no physical exertion at all) to 20 (maximal physical exertion possible).

How to Use the Perceived Exertion Scale

According to the CDC, to use the Perceived Exertion Scale, an individual needs to rate his or her perceived level of exertion while performing physical activity. This rating should reflect how heavy and strenuous the exercise feels to the person, combining all sensations and feelings of physical stress, effort and fatigue. Focus should not be put on any one factor such as leg pain or shortness of breath, but on the total feeling of exertion. The individual will then choose the number between 6 (again, no exertion at all) and 20 (maximal exertion) that best describes his or her level of exertion. To help gauge the meaning of the scale numbers, the following guide may be used:

• A rating of nine corresponds to "very light" exercise. For a healthy person, it is like walking slowly for some minutes.
• A rating of 13 corresponds to "somewhat hard" exercise; the exercise is strenuous but it still feels okay to continue.
• A rating of 17 is considered "very hard" and is very strenuous. A healthy person can still continue, but he or she must push him or herself. It feels very intense, and the person is very tired.
• A rating of 19 on the scale is an extremely strenuous exercise level. For most people this is the most strenuous exercise they have ever experienced.

According to Borg’s Perceived Exertion and Pain Scales, there is a high correlation between a person’s perceived exertion rating — multiplied by ten — and the actual heart rate during physical activity. This means that a person’s exertion rating may provide a fairly good estimate of the actual heart rate during activity. For example, if a person’s RPE is 12, and 12 x 10 = 120, his or her heart rate should be approximately 120 beats per minute. It is important to note that this calculation is only an approximation of heart rate; the actual heart rate can vary considerably depending on age and physical condition. The Borg Rating of Perceived Exertion is also the preferred method to assess intensity among individuals who take medications that may affect heart rate or pulse.

In order for the scale to be used effectively, individuals will need to appraise their feelings of exertion as honestly as possible without thinking about what the actual physical workload may be. Assigning the number that best describes the level of exertion will give the individual a good idea of the intensity level of his or her activity. This information can be used to speed up or slow down movements in order to reach the desired range.

The "Talk Test"

A third, and by far the simplest, method to gauge the level of exercise intensity is the "Talk Test." According to the CDC, as a rule of thumb, if a person is performing a moderate–intensity activity, he or she will be able to talk, but not sing, during the activity. If an individual is performing a vigorous–intensity activity, he or she will not be able to say more than a few words without pausing for a breath. Research published in the September 2004 issue of Medicine & Science in Sports and Exercise, the official scientific journal of the American College of Sports Medicine, found that people who could talk comfortably during exercise were likely to be working at the appropriate intensity. When comfortable speech was no longer possible, the exercise intensity was greater than what is normally recommended.

Why It Is Important to Know the Exercise Intensity Level?

According to the 2008 Physical Activity Guidelines for Americans, individuals need to perform two types of physical activity each week to improve their health: aerobic exercise and muscle–strengthening. For aerobic exercise, the Guidelines recommend:

• Two hours and thirty minutes of moderate–intensity aerobic activity every week, or
• One hour and fifteen minutes of vigorous–intensity aerobic activity every week, or
• An equivalent mix of moderate and vigorous–intensity aerobic activity on two or more days a week

In order to follow these guidelines, it is necessary for individuals to be able to evaluate the intensity level at which they are exercising. Individuals should find the method that they are most comfortable with and start moving. Regular physical activity can help people of all ages to feel better, look great and live a longer, healthier life.

MEDICAL DISCLAIMER: The information is not intended to constitute medical advice and is not a substitute for consultation with a physician or other health care provider. Individuals with specific complaints should seek immediate consultation from their personal physicians.