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The heart rate is the number of contractions of the heart in one minute. It is measured in beats per minute (bpm). When resting, the adult human heart beats at about 70 bpm (males) and 75 bpm (females), but this rate varies between people.
The body can increase the heart rate in response to a wide variety of conditions in order to increase the cardiac output (the amount of blood ejected by the heart per unit time). Exercise causes a normal person's heart rate to increase above the resting heart rate. As the physical activity becomes more vigorous, the heart rate increases more. With very vigorous exercise, a maximum heart rate can be reached.
The pulse is the most straightforward way of measuring the heart rate, but it can be deceptive when some strokes do not lead to much cardiac output. In these cases (as happens in some arrhythmias), the heart rate can be (much) higher than the pulse.
Control of heart rate
The heart contains cardiac pacemakers that spontaneously cause the heart to beat. These can be controlled by the autonomic nervous system and circulating adrenaline. The heart beats more quickly than average in an obese person, and less quickly than average in athletes.
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 is close to the surface. Such places are wrist (radial artery), neck (carotid artery), elbow (brachial artery), and groin (femoral artery).
- Another method of measuring heart rate is using a commercially avaliable heart rate monitor. These work by a chest strap that senses the heart rate using electrodes. The signal is then transmitted to a wrist receiver for display. These allow accurate measurements to be continuously taken and can be used during exercise when manual measurement would be difficult or impossible (such as when the hands are being used).
- In hospitals, an electrocardiograph is used to measure heart rates.
Resting Heart Rate (RHR)
This is a person's heart rate when they are not doing any activities. It is usually taken first thing in the morning, before even getting out of bed. Measuring the RHR every day is a good way of detecting possible illness, as the RHR will be elevated by 8-10 beats if the immune system is attempting to fight something.
Maximum Heart Rate (MHR)
This is the maxiumum heart rate that a person is capable of. It is linked to age, current fitness level, and previous years of training.
Measuring MHR
The only accurate way of measuring MHR is for a person to exercise and increase the intensity until they can no longer continue - they will hit their MHR just before exhaustion. A less painful way is to use the formula:
- MHR = 200 - Age
It has been suggested by others that the relationship to age is not a linear one and the following formulae have been suggested.
Londeree and Moeschberger from the University of Missouri-Columbia:
- MHR = 206.3 - (0.711 * Age)
Miller et al from Indiana University:
- MHR = 217 - (0.85 * Age)
However, any of these formulae can be incorrect by upto 10 beats.
Exercise Type
The MHR an individual can achieve is based on the type of exercise being undertaken. Generally exercise where the whole body weight is used (e.g. running) have higher MHR than when the body is completely or partially supported (e.g. cycling or swimming).
Relative to treadmill running:
Heart rate abnormalities
Tachycardia
Main article: Tachycardia
A tachycardia is a heart rate more than 100 beats per minute.
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. 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 it.
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