A heart rate monitor is a personal monitoring device that allows you to measure your heart rate in real time or record your heart rate for later study. It is used to a large extent by performers of various types of physical exercise.
The first models consisted of a monitoring box with a set of electrode cables that were attached to the chest. The first EKG wireless heart rate monitor was invented in 1977 by Seppo Säynäjäkangas as an aid to the formation of the Finnish national cross-country team. As 'intensity training' became a popular concept in athletic circles in the mid-1980s, retail sales of wireless personal heart monitors began in 1983.
Modern heart rate monitors generally comprise two elements: a chest strap transmitter [needs updating] and a wrist receiver (which usually doubles as a watch) or mobile phone. In the first plastic straps, water or liquid was required to obtain good performance. Later units have used conductive intelligent tissue with built-in microprocessors that analyze the EKG signal to determine heart rate. The latest devices use optics to measure heart rate using infrared light. This is achieved by producing infrared light by an internal light bulb, since infrared light is absorbed by the blood, a sensor measures how much infrared light is obscured by. If it is significantly darker due to the pulse causing a temporary increase in the amount of blood that is traveling through the measured area, it is counted as a heart rate.
Strapless heart rate monitors (often referred to as "laptops") now allow the user to touch only two sensors on a wristwatch display for a few seconds to view heart rate data. These are popular for comfort and ease of use, although they do not give as much detail as the monitors that use a chest strap. Some models of these variations of heart rate monitors use an infrared sensor to measure heart rate, as opposed to two electrodes.
The most advanced models offer measurements of heart rate variability, activity and respiratory rate to assess parameters related to the 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 on the fabric.
In older versions, when a heartbeat 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 encoded chest strap signal (such as Bluetooth, ANT or other low power radio link); The latter prevents a user's receiver from using signals from other nearby transmitters (known as crossover interference).
The latest versions include a microprocessor, which is continuously monitoring the EKG and calculating heart rate, and other parameters. These can include accelerometers that can detect speed and distance, eliminating the need for foot devices.
There are a large number of receiver designs, with several features. These include the average heart rate during the exercise period, time in a specific heart rate zone, burned calories, respiratory rate, speed and distance built in and detailed recording that can be downloaded to a computer. The receiver can be incorporated into a smartwatch or smartphone. Wrist bands with integrated sensor work optically and have poor accuracy.