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A heart rate monitor is a personal monitoring device that allows a subject to measure their heart rate in real time or record their heart rate for later study. Early models consisted of a monitoring box with a set of electrode leads that attached to the chest. While these still exist, modern versions usually consist of two elements: a chest strap transmitter and a wrist receiver or mobile phone (which usually doubles as a watch or phone). In early plastic straps water or liquid was required to get good performance. Later units have used conductive smart fabric ( Polar, Textronics and Zephyr) with built in microprocessors that analyze the EKG signal to determine Heart rate ( Polar and Zephyr).

Strapless heart rate monitors are available as well, but lack some of the functionality of the original design. Advanced models additionally measure heart rate variability, activity, and breathing rate to assess parameters relating to a subjects fitness. Some newer monitors have replaced the plastic straps with fabric sensors for comfort or garment integration. The new smart fabric technology has some promise to eliminate the need for elastic straps that hold the transmitter with embedded electrodes in contact with the chest.

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 users receiver from using signals from other nearby transmitters (known as cross-talk interference). Newer versions include a microprocessor that is continuously monitoring the EKG and calculating the heart rate, r to r and other parameters. These can 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.


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