Heart rate

Age	Normal heart rate (beats per minute)
Newborn	120
Older Child	90-110
Adult	50-100

Heart rate (HR) is the average resting heartbeat per minute of the heart. When resting, the average adult human heart beats at about 70 beats per minute (bpm) in males and 75 bpm in females. This rate varies among different people, and can be significantly lower in individuals who participate in endurance athletics. Heart rate is determined by measuring one's pulse using a variety of methods. These can be specialized devices, or merely pressing one's fingers against an artery.

It is generally accepted that listening to heart beats using a stethoscope, a process known as auscultation, is a more accurate method of measuring the heart rate.

Measuring heart rate

Measuring the pulse at the neck and wrist.

The pulse rate can also be measured at any point on the body where an artery pulsation is transmitted to the surface - often as it is compressed against an underlying structure like bone - by pressuring it with the index and middle finger. The thumb should never be used for measuring another person's heart rate, as its strong pulse may interfere with discriminating the site of pulsation, causing a miscount. Some commonly palpated sites include:

1. The ventral aspect of the wrist on the side of the thumb (radial artery)
2. The ulnar artery
3. The neck (carotid artery),
4. The inside of the elbow, or under the biceps muscle (brachial artery)
5. The groin (femoral artery)
6. Behind the medial malleolus on the feet (posterior tibial artery)
7. Middle of dorsum of the foot (dorsalis pedis).
8. Behind the knee (popliteal artery)
9. Over the abdomen (abdominal aorta)
10. The chest (aorta), which can be felt with one's hand or fingers. However, it is possible to auscultate the heart by utilizing a stethoscope.
11. The temple

A more precise method of determining pulse involves the use of an electrocardiograph, or ECG (also abbreviated EKG). Continuous electrocardiograph monitoring of the heart is routinely done in many clinical settings, especially in critical care medicine. Commercial heart rate monitors are also available, consisting of a chest strap with electrodes. The signal is transmitted to a wrist receiver for display. Heart rate monitors allow accurate measurements to be taken continuously and can be used during exercise when manual measurement would be difficult or impossible (such as when the hands are being used).

Maximum heart rate

Maximum heart rate (MHR, also called STD, or HR_max) is the highest number of times your heart can contract in one minute, or the heart rate that a person could achieve during maximal physical exertion. It is not the maximum one should obtain often during exercise. HR_max is used as a base number to calculate target heart rate for exercise (see below). The average adult heart beats about 60 to 80 times a minute at rest. The resting heart rate usually rises with age, and it's generally lower in physically fit people. Resting heart rate is used to determine one's training target heart rate. Athletes sometimes measure their resting heart rate as one way to find out if they're over trained. The heart rate adapts to changes in the body's need for oxygen, such as during exercise or sleep. Care is required because if it gets too high, you could pass out and die.

Measuring HR_max

Fox and Haskell formula

The most accurate way of measuring HR_max for an individual is via a cardiac stress test. In such a test, the subject exercises while being monitored by an EKG. During the test, the intensity of exercise is periodically increased (if a treadmill is being used, through increase in speed or slope of the treadmill), or until certain changes in heart function are detected in the EKG, at which point the subject is directed to stop. Typical durations of such a test range from 10 to 20 minutes.

Conducting a maximal exercise test can require expensive equipment. If you are just beginning an exercise regimen, you should only perform this test in the presence of medical staff due to risks associated with high heart rates. Instead, people typically use a formula to estimate their individual Maximum Heart Rate. The most common formula encountered is:

HR_max = 220 − age

This is attributed to various sources, often "Fox and Haskell." While the most common (and easy to remember and calculate), this particular formula is not considered by some to be a good predictor of HR_max.

A 2002 study of 43 different formulae for HR_max (including the one above) concluded the following:

1) No "acceptable" formula currently existed, (they used the term "acceptable" to mean acceptable for both prediction of $V_{\mathrm {O} _{2}max}$, and prescription of exercise training HR ranges)

2) The most decent formula of those examined was:

HR_max = 205.8 − (0.685 × age)

This was found to have a Standard Deviation that, although large (6.4 bpm), was still deemed to be acceptable for the use of prescribing exercise training HR ranges.

Other often cited formulas are:

HR_max = 206.3 − (0.711 × age)

(Often attributed to "Londeree and Moeschberger from the University of Missouri–Columbia")

HR_max = 217 − (0.85 × age)

(Often attributed to "Miller et al. from Indiana University")

These figures are still dependent on physiology and fitness; for example an endurance runner's rates will typically be lower due to the increased size of the heart required to support the exercise, while a sprinter's rates will be higher due to the improved response time and short duration., etc. may each have predicted heart rates of 180 (= 220-Age), but these two males could have actual Max HR 20 beats apart (e.g. 170-190).

Recovery heart rate

This is the heart rate measured at a fixed (or reference) period after ceasing activity; typically measured over a 1 minute period.

Heart-Rate Recovery Immediately after Exercise as a Predictor of Mortality

For death, it has been hypothesized* that a delayed fall in the heart rate after exercise might be an important prognostic marker.

• Study by: Christopher R. Cole, M.D., Eugene H. Blackstone, M.D., Fredric J. Pashkow, M.D., Claire E. Snader, M.A., and Michael S. Lauer, M.D. ; Art. ref. from the NEJM, Volume 341:1351-1357 October 28, 1999 Number 18

Target heart rate

The Target Heart Rate (THR), or Training Heart Rate, is a desired range of heart rate reached during aerobic exercise which enables one's heart and lungs to receive the most benefit from a workout. This theoretical range varies based on one's physical condition, gender, and previous training. Below are two ways to calculate one's Target Heart Rate. In each of these methods, there is an element called "intensity" which is expressed as a percentage. The THR can be calculated by using a range of 50%–85% intensity. However, it is crucial to derive an accurate HR_max to ensure these calculations are meaningful (see above).

Karvonen method

The Karvonen method factors in Resting Heart Rate (HR_rest) to calculate Target Heart Rate (THR):

THR = ((HR_max − HR_rest) × %Intensity) + HR_rest

Example for someone with a HR_max of 180 and a HR_rest of 70:
50% intensity: ((180 − 70) × 0.50) + 70 = 125 bpm
85% intensity: ((180 − 70) × 0.85) + 70 = 163 bpm

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Zoladz method

An alternative to the Karvonen method is the Zoladz method, which derives exercise zones by subtracting values from HR_max.

THR = HR_max – Adjuster ± 5 bpm

Zone 1 Adjuster = 50 bpm

Zone 2 Adjuster = 40 bpm

Zone 3 Adjuster = 30 bpm

Zone 4 Adjuster = 20 bpm

Zone 5 Adjuster = 10 bpm

Example for someone with a HR_max of 180:
Zone 1 (easy exercise) : 220 − age = 0; * 65 → 125

Zone 2 (tough exercise): 220 − age = 0; * 85 → 155

Heart rate reserve

Heart rate reserve (HRR) is a term used to describe the difference between a person's measured or predicted maximum heart rate and resting heart rate. Some methods of measurement of exercise intensity measure percentage of heart rate reserve. Additionally, as a person increases their cardiovascular fitness, their HR_rest will drop, thus the heart rate reserve will increase. Percentage of HRR is equivalent to percentage of VO₂ reserve.

HRR = HR_max − HR_rest

Heart rate abnormalities

Tachycardia

Main article: Tachycardia

Tachycardia is a resting heart rate more than 100 beats per minute. This number can vary as smaller people and children have faster heart rates than average adults.

Bradycardia

Main article: Bradycardia

Bradycardia is defined as a heart rate less than 60 beats per minute although it is seldom symptomatic until below 50 bpm when a human is at total rest. Trained athletes tend to have slow resting heart rates, and resting bradycardia in athletes should not be considered abnormal if the individual has no symptoms associated with it. Again, this number can vary as smaller people and children have faster heart rates than adults.

Miguel Indurain, a cyclist and five time Tour de France winner, had a resting heart rate of 28 beats per minute, one of the lowest ever recorded in a healthy human.

Heart rate as a risk factor

An Australian led international study of patients with cardiovascular disease has shown that heart beat rate plays a key role in the risk of heart attack. The study, published in The Lancet (Sept 2008) studied 11,000 people, across 33 countries, who were being treated for heart problems. Those patients whose heart rate was above 70 beats per minute had significantly higher incidence of heart attacks, hospital admissions and the need for surgery. University of Sydney professor of cardiology Ben Freedman from Sydney's Concord hospital, said "If you have a high heart rate there was an increase in heart attack, there was about a 46 percent increase in hospitalizations for non-fatal or fatal heart attack."

See also

• Athlete's heart
• Blood flow
• Cardiology
• Cardiac pacemaker
• Pulse