Heart rate monitors (HRM) measure the intensity of your exercise by recording the frequency of your heartbeats using a chest-mounted electrocardiogram (ECG or EKG). They work by detecting the small electric voltages emitted with each heartbeat, which they then transmit in the form of electromagnetic signals. A wrist strap that doubles as a watch receives and then processes the signals according to your programmed criteria.



People use HRMs because how you feel when you exercise doesn't always give a good indication of how intensely you are exercising and can be due to other factors. While heart rate can also be measured by taking a pulse, it is a pain to do this while you are exercising since you'll need to keep stopping and starting.

For people who exercise frequently, are training for a sports event, rehabilitating after an accident, trying to lose weight or improving their body condition, heart rate is an important indicator of performance and the strain that exercise is putting your body under. It also allows you to ascertain your initial fitness level and improvement over time by comparison.

Heart rate monitors can be used to pre-determine a particular range that remains your target (Target Heart Rate or THR), and will bleep when you reach this level of exertion. The target is a percentage of the average maximum heart rate capacity for your age or fitness level, which will reflect your particular aims for that exercise period. If it is weight loss, endurance or recovery you are aiming at, you'll need to increase your heart rate to between 60-70% of the max rate; if it's for cardiovascular training you could be looking at 70-80%. Interval training, which is used by athletes to build stamina, will require a limited-duration increase in heart rate to 80% or more.

When you exercise, your heart pumps blood to the lungs where it is oxygenated before being passed to the muscles, which use oxygen as fuel. The harder you exercise, the more air your muscles need and the harder your heart needs to beat. Over time your heart will become stronger and need less beats to pump the same amount of air. Hence, those who are fitter have a lower figure than average both in sport and at rest, and will recover faster.

Basic heart rate monitors will show whether you are achieving your target zone, give you a constant readout of your rate, and record the amount of time you have spent exercising. More advanced devices provide a stopwatch, and allow you to record information such as lap time, distance travelled, and pre-record more than one training programme. They may allow you to calculate performance over time, both at rest and during sport, as well as recovery time, which will help you feel you are achieving success in your training.

More expensive heart rate monitors encode information from the transmitter in a way that prevents them picking up signals from nearby devices. Other information such as heart rate variability, calories burned, and maximal oxygen uptake (VO2 max) can also be stored in information logs that can then be downloaded to the internet. If they are to be used for cycling or running HRMs can also indicate things like direction, atmospheric pressure and altitude.

A scientist at the University of Oulu invented the first wireless heart rate monitor as a training tool for the Finnish national cross-country skiing team. His company, Polar Electro went on to manufacture heart rate monitors for individuals, which became popular with athletes in the 80s as they saw the benefits of intensity training. These days, heart rate products are popular with individuals and professional athletes alike, and the can include shirts with in-built monitors, and gym equipment that offers HRM. Rather than being a luxury, they form an essential part of everyday fitness training.