Heart rate is determined by the number of heartbeats per unit of time, typically expressed as beats per minute (BPM), it can vary with as the body's need for oxygen changes, such as during exercise or sleep. The measurement of heart rate is used by medical professionals to assist in the diagnosis and tracking of medical conditions. It is also used by individuals, such as athletes, who are interested in monitoring their heart rate to gain maximum efficiency from their training.
Heart rate is measured by finding the pulse of the body. This pulse 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 - by pressuring it with the index and middle finger. The thumb should not be used for measuring another person's heart rate, as its strong pulse may interfere with discriminating the site of pulsation 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 using a stethoscope.
- The temple
- The lateral edge of the mandible
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).
Measuring HR max
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.
Formula for HR max
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:
This is attributed to various sources, often "Fox and Haskell," and was devised in 1970 by Dr. William Haskell and Dr. Samuel Fox. Inquiry into the history of this formula reveals that it was not developed from original research, but resulted from observation based on data from approximately 11 references consisting of published research or unpublished scientific compilations. 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 reputable health and fitness professionals to be a good predictor of HR max . Despite the widespread publication of this formula, research spanning two decades reveals its large inherent error (Sxy=7-11 b/min). Consequently, the estimation calculated by HRmax=220-age has neither the accuracy nor the scientific merit for use in exercise physiology and related fields.
A 2002 study of 43 different formulae for HR max (including the one above) concluded the following:
Other often cited formulae are:
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 people 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.
For death, it has been hypothesized* that a delayed fall in the heart rate after exercise might be an important prognostic marker. Less than 30 bpm reduction at one minute after stopping hard exercise was a predictor of heart attack. More than 50 bpm reduction showed reduced risk of heart attack.
Training regimes sometimes use recovery heart rate as a guide of progress and to spot problems such as overheating or dehydration . After even short periods of hard exercise it can take a long time (about 30 minutes) for the heart rate to drop to rested levels.
Devices with built in accelletry and heart rate sensors can automatically measure heart rate recovery. For instance the BioHarness can be used to measure heart recovery as the device also logs and transmits the vector magnitude units of the person acceleration. The acceleration number is used to determine when the person is moving and at rest and hence detect the start time for the heart rate recovery period.
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).
Example for someone with a HR max of 180 (age 40, estimating HR max as 220 − age):
65% intensity: (220 − (age = 40)) * 0.65 → 117 bpm
85% intensity: (220 − (age = 40)) * 0.85 → 153 bpmKarvonen method
The Karvonen method factors in Resting Heart Rate (HR rest ) to calculate Target Heart Rate (THR):
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 bpmZoladz method
An alternative to the Karvonen method is the Zoladz method, which derives exercise zones by subtracting values from HR max .
Example for someone with a HR max of 180:
Zone 1 (easy exercise) : 180 − 50 + 5 → 135 bpm
Zone 4 (tough exercise): 180 − 20 + 5 → 165 bpmHeart 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 VO 2 reserve.
Heart rate abnormalities
Tachycardia
Main article: TachycardiaTachycardia 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: BradycardiaBradycardia 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 ath
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