Resting heart rate refers to the number of times the heart beats per minute when an individual is at complete rest. A normal resting heart rate for adults ranges from 60 to 100 beats per minute (bpm). A slower-than-normal resting heart rate (less than 60 bpm) is referred to as bradycardia. A faster-than-normal resting heart rate (greater than 100 bpm) is referred to as tachycardia.
An accurate measure of resting heart rate is important for many reasons. Resting heart rate is a good indicator of the overall health of an individual. Although a normal and healthy resting heart rate for adults ranges from 60 to 100 bpm; in more active and fit individuals, resting heart rate values can be less than 60 bpm. In fact, in some elite endurance-trained individuals, resting heart rate values can be in the vicinity of 40 bpm. On the other end of the spectrum, research indicates that individuals with resting heart rates closer to 100 bpm have increased cardiovascular and all-cause mortality risk. Measurement of resting heart rate is also an important skill for evaluating the effectiveness of exercise programs and monitoring training intensity. Indeed, the calculation of target heart rates for exercise prescription is predicated on an accurate measure of resting heart rate, as indicated in the sidebar.
Resting heart-rate measurement should be performed immediately in the morning after awakening from a good night of sleep. If this is not possible, an individual should rest for 5–10 minutes in a supine or seated position prior to obtaining the resting heart-rate measure. Resting heart rate should be obtained by counting the number of times the heart beats for 60 seconds. A device that counts seconds will be required, such as a clock or watch with a second hand, a stopwatch, or a mobile phone stopwatch app.
If the resting heart rate is measured by auscultation, a stethoscope and a device that counts seconds are required. The bell of the stethoscope should be placed to the left side of the sternum. The practitioner should count the sounds of the heart for 60 seconds. To lessen the time of invasiveness of auscultation, it is acceptable to count the sounds of the heart for 30 seconds and multiply by two to convert to bpm.
If the resting heart rate is measured by palpation, the practitioner can check the pulse at various anatomical sites:
The electrocardiogram, abbreviated as either EKG or ECG, is a common and powerful tool used by EMTs and emergency rooms in life-threatening situations (often in conjunction with a defibrillator), by physicians diagnosing or monitoring heart disease, and by physiologists studying the cardiac system. The ECG is an electrical image that reflects the mechanical functioning of the heart. The electrical conduction system of the heart is highly organized. Muscle contraction (shortening) begins with an electrical signal called depolarization. When an electrical impulse is spread through the cardiac muscle fibers, a small amount of the current is released into the fluid surrounding the heart and spreads out to the surface of the skin. The ECG electrodes detect this electrical activity, and it is amplified and recorded on the ECG screen or paper. The vertical axis of the ECG strip, then, is electrical potential measured in millivolts, and the horizontal axis is time. The resting ECG is usually a clean tracing, thus, it is easy to interpret and provide an accurate resting heart rate measurement.
Natural day-to-day variability in the resting heart rate ranges from 2 to 4 bpm under laboratory-controlled conditions. Resting heart rate will decrease as the heart becomes stronger with regular aerobic exercise. Consequently, a lower resting heart rate is typically a good indicator of overall cardiorespiratory fitness. Resting heart rate decreases with training because the left ventricular wall of the heart becomes stronger, and therefore each heart beat results in a great volume of blood being ejected from the left ventricle. This training effect is referred to as an increase in stroke volume. Research has reported that resting heart rate can be decreased by 10–20 bpm with training. In contrast, too much training can lead to an increase in resting heart rate. In fact, many athletes and recreational enthusiasts use resting heart rate as a method to monitor training recovery. A persistent increase in resting heart rate following training and/or races may represent overtraining and signify that additional rest is needed.
Resting heart rate can be influenced by acute exposure to various environmental stressors, such as altitude and heat. When individuals ascend to moderate altitudes (e.g., between 5,000 and 10,000 feet), numerous physiological responses occur in the human body. To increase the oxygen-carrying capacity of the blood in higher altitudes, a natural diuretic effect occurs, with a subsequent increase in urine output. This response decreases the overall plasma volume and concurrently reduces stroke volume. To maintain overall cardiac output, the body compensates for the reduced stroke volume with an increase in resting heart rate. The altitude-induced increase in resting heart rate gradually subsides over the course of several weeks as the body acclimates to the higher elevation. Similar to altitude exposure, exposure to hot and/or humid environmental conditions can also affect the resting heart rate. The body's natural physiological response to heat stress is increased sweating. Without adequate fluid intake to offset the increased sweating, an individual can become dehydrated. Dehydration leads to reductions in plasma volume and stroke volume. The body offsets these physiological changes by augmenting resting heart rate. Typically, an individual acclimatizes to hot and/or humid environmental conditions over the course of 10–14 days, and resting heart rate gradually returns to normal levels.
Medications can also affect resting heart rate. Betablockers and calcium-channel blockers are commonly prescribed medications for hypertension and heart disease. In fact, between 10%–30% of adults in the United States are prescribed beta-blockers. Beta-blockers result in both decreased resting and exercise heart rates. Commonly prescribed beta-blockers include atenolol, metoprolol, and propranolol. Because betablockers reduce resting heart rate, traditional methods for establishing target heart rate (e.g., heart rate reserve method) will be invalid. Therefore, practitioners should recommend an alternative method for setting target exercise intensity for individuals taking a beta-blocker. The rating of perceived exertion (RPE) scale is an excellent option.
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American College of Sports Medicine (ACSM), 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 637-9200, Fax: (317) 634-7817, http://www.acsm.org .
American Council on Exercise, 4851 Paramount Dr., San Diego, CA, 92123, (858) 576-6500, (888) 825-3636, ext. 782, Fax: (858) 576-6564, https://www.acefitness.org .
American Heart Association (AHA), 7272 Greenville Ave., Dallas, TX, 75231, (800) 242-8721, http://www.heart.org .
Lance C. Dalleck, PhD