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Heart rate
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Heart rate (HR) is a measure of the number of heart beats per minute (bpm).
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Encyclopedia
| Age | Normal heart rate
(beats per minute) |
|---|
| Newborn | 120 | | Older Child | 90-110 | | Adult | 50-100 | |
Heart rate (HR) is a measure of the number of heart beats per minute (bpm). The average resting human heart rate is about 70 bpm for adult males and 75 bpm for adult females. Heart rate varies significantly between individuals based on fitness, age and genetics. Endurance athletes often have very low resting heart rates. Heart rate can be measured by monitoring one's pulse. Pulse measurement can be achieved used specialized medical devices, or by merely pressing one's fingers against an artery (typically on the wrist or the neck).
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
The pulse rate can also 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 - 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:
- The ventral aspect of the wrist on the side of the thumb (radial artery)
- The ulnar artery
- The neck (carotid artery),
- The inside of the elbow, or under the biceps muscle (brachial artery)
- The groin (femoral artery)
- Behind the medial malleolus on the feet (posterior tibial artery)
- Middle of dorsum of the foot (dorsalis pedis).
- Behind the knee (popliteal artery)
- Over the abdomen (abdominal aorta)
- 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.
- 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 HRmax) 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. HRmax 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 HRmax
The most accurate way of measuring HRmax 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.
Formulas for HRmax
Various formulas are used to estimate individual Maximum Heart Rates, based on age, but maximum heart rates vary significantly between individuals.
Even within a single elite sports team, such as Olympic rowers in their 20s, maximum heart rates can vary from 160 to 220. This variation is as large as a 60 or 90 year age gap by the linear equations given below, and indicates the extreme variation about these average figures.
The most common formula encountered, with no indication of standard deviation, is:
- HRmax = 220 − age
This is attributed to various sources, often "Fox and Haskell," and was devised in 1970 by Dr. William Haskell and Dr. Samuel Fox. It gained widespread use through being used by Polar Electro in its heart rate monitors, which Dr. Haskell has "laughed about", as it "was never supposed to be an absolute guide to rule people's training."
While the most common (and easy to remember and calculate), this particular formula is not considered by some to be a good predictor of HRmax.
A 2002 study of 43 different formulae for HRmax (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 , and prescription of exercise training HR ranges)
- 2) The most decent formula of those examined was:
HRmax = 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:
- HRmax = 206.3 − (0.711 × age)
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- HRmax = 217 − (0.85 × age)
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These figures are very much averages, and depend greatly on individual 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).
Further, note that individuals of the same age, the same training, in the same sport, on the same team, can have actual Max HR 60 bpm apart (160 to 220): the range is extremely broad, and some say "The heart rate is probably the least important variable in comparing athletes."
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-October 28, 1357, 1999 Number 18
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 HRrest will drop, thus the heart rate reserve will increase. Percentage of HRR is equivalent to percentage of VO2 reserve.
- HRR = HRmax − HRrest
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 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 Spanish 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 (September 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
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