Heart rate monitor
- This article refers to a device used by non-scientists. For the article on the medical device performing a similar function, see Electrocardiography.
A heart rate monitor is a personal monitoring device that allows one to measure one's heart rate in real time or record the heart rate for later study. It is largely used by performers of various types of physical exercise.
Early models consisted of a monitoring box with a set of electrode leads which attached to the chest. The first wireless EKG heart rate monitor was invented in 1977 by Seppo Säynäjäkangas, as a training aid for the Finnish National Cross Country Ski team. As 'intensity training' became a popular concept in athletic circles in the mid-80s, retail sales of wireless personal heart monitors started from 1983.
Modern heart rate monitors usually comprise two elements: a chest strap transmitter and a wrist receiver (which usually doubles as a watch) or mobile phone. In early plastic straps, water or liquid was required to get good performance. Later units have used conductive smart fabric with built-in microprocessors that analyze the EKG signal to determine heart rate. More recent devices utilise optics to measure heart rate using Infrared light. This is achieved by production of infrared light by an internal bulb, as Infrared light is absorbed by the blood, a sensor measures the amount that the infrared light is darkened by. If it is significantly darker, due the pulse causing a temporary increase in the amount of blood that is travelling through the measured area, that is counted as a pulse.
Strapless heart rate monitors (often referred to as "wearables") now allow the user to just touch two sensors on a wristwatch display for a few seconds to view heart rate data. These are popular for comfort and ease of use, though they don't give as much detail as monitors that use a chest strap. Some models of these variations of heart rate monitors utilise an infrared sensor to measure the heart rate, as opposed to two electrodes.
More advanced models offer measurements of heart rate variability, activity, and breathing rate to assess parameters relating to a subject's fitness. Sensor fusion algorithms allow these monitors to detect core temperature and dehydration.
Another style of heart rate monitor replaces the plastic around-the-chest strap with fabric sensors - the most common of these is a sports bra for women that includes sensors in the fabric.
In old versions, when a heart beat is detected a radio signal is transmitted, which the receiver uses to determine the current heart rate. This signal can be a simple radio pulse or a unique coded signal from the chest strap (such as Bluetooth, ANT, or other low-power radio link); the latter prevents one user's receiver from using signals from other nearby transmitters (known as cross-talk interference).
Newer versions include a microprocessor, which is continuously monitoring the EKG and calculating the heart rate, and other parameters. These may include accelerometers that can detect speed and distance, eliminating the need for foot worn devices.
There are a wide number of receiver designs, with various features. These include average heart rate over exercise period, time in a specific heart rate zone, calories burned, breathing rate, built-in speed and distance, and detailed logging that can be downloaded to a computer. The receiver can be built into a smartwatch or smartphone. Wrist bands with integrated sensor work optically, and have poor accuracy.
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