Heart rate is the number of heart beats per unit of time, usually expressed as beats per minute.

When resting, the average adult human heart beats at about 70 bpm (males) and 75 bpm (females); however, this rate varies among people and can be significantly lower in endurance athletes. The infant/neonatal rate of heartbeat is around 130-150 bpm, the toddler's about 100–130 bpm, the older child's about 90–110 bpm, and the adult's about 80–100 bpm. 75 beats per minute translates to 4500 beats an hour, 108,000 beats per day, or about 39,420,000 beats in a year.

The pulse is the most commonly used method of measuring the heart rate. This method may be inaccurate in cases of low cardiac output, as happens in some arrhythmias, where the heart rate may be considerably higher than the pulse rate.

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 (which in most people is identical to the heart rate) can be measured at any point on the body where an artery's pulsation is transmitted to the surface - often as it is compressed against an underlying structure like bone. Some commonly palpated sites are as listed.

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

NOTE: 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, and you may count the thumb's pulse accidentally when measuring'^[2] (Of course, this is a non-issue when measuring your own pulse). Producing an electrocardiogram, or ECG (also abbreviated EKG), is one of the most precise methods of heart rate measurement. Continuous electrocardiographic 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 (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. MHR is used as a base number to calculate target heart rate for exercise (see below).^[3] The heart beats about 60 to 80 times a minute when we're at rest. 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.

Measuring HR_max

Fox and Haskell formula

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 (caution: can vary significantly!)

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 ^[4] 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 accurate 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 formulae 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. Also, population averages are just that. Two 40-year-old males with same height, weight, strength, 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). It's important not to guess.

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

The increase in heart rate that accompanies exercise is due in part to a reduction in vagal tone. Recovery of the heart rate immediately after exercise is a function of vagal reactivation. Because a generalized decrease in vagal activity is known to be a risk factor 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

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, age, 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. THR can be calculated by using a range of 50%–85% intensity. However, it is crucial one have an accurate MHR calculation first to ensure these calculations are meaningful (see above).

Affecting heart rate

Changes in heart rate can be for a range of reasons; illness, fatigue, drug use, arousal, stress and anxiety; highly aroused individuals are mentally and physically activated; they experience increased heart rate, respiration and sweating.

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

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 mpg32

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

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

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

Bradycardia is defined as a heart rate less than 60 beats per minute although it is seldom symptomatic until below 50 bpm. 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.^[5]

See also

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

References

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