1. DETECTING BLOOD FLOW IN THE CAPILLARIES OF AN EAR LOBE OR FINGER.

 The most basic of this type of monitor has a small infrared sensor under a little window on the surface of the monitor. These units are either a small hand held unit or wrist watch style. The user places a finger tip or thumb over this window and the infrared sensor detects tiny changes in infrared due to the pulsing of the blood in the capillaries with each heart beat. These have the disadvantage that motion will cause changes in the infrared signal detected.
Another type of infrared system places the sensor in a small clip that clips to an earlobe. The ear lobe clip infrared sensor types typically are a small square or rectangular unit designed to mount on the handle bars of exercise bikes, stair climbers, etc. A small wire goes from the readout unit to the ear clip. The advantages of this type are: 1. often mounted permanently on exercise equipment so that it is very handy to use when the person starts to use the equipment. All that is necessary is to clip on the ear lobe sensor and turn on; and 2. ideal for multiple users in a health club setting. Disadvantages of this type are: 1. head motion and flickering or changing light conditions can cause errors; 2. some people may find the small wire between the sensor and readout unit distracting and; 3. not as convenient or portable as wristwatch style units. It should be noted that one brand, the Cateye, uses a highly advanced ear lobe sensor which greatly reduces the effect of head motion and light mentioned in 1.

2. ELECTRICAL DETECTION OF HEART EKG SIGNAL IN THE HAND AREA.

 These heart rate monitors sense the electrical signal that triggers the heart muscle. This signal, which is strong in the chest area, can also be detected in the hands or fingers, although it is much weaker than in the chest area. Typically, heart rate monitors using this system have two metal contact points which are touched or grasped with the hands or fingers, one hand or finger on one contact, the other hand or finger on the other contact. The advantages of these heart rate monitors are: 1. self-contained and portable - most are easily passed around among people in a group and 2. can be mounted permanently on exercise equipment or a wall, making them instantly ready for use by multiple users in a health club setting. The disadvantages of this system are: 1. requires users to stop moving their hands and arms and place their hands on the monitor contacts; 2. there is a delay of a few seconds from when the electrodes are contacted and when the unit will display the pulse rate, and; 3. these are suitable only for periodic checks of heart rate while exercising and not for continuous monitoring.

3. DETECTING THE HEART EKG SIGNAL IN THE CHEST AREA WITH ELECTRODES.

 These monitors also sense the heart EKG signal, but on the chest where it is strongest. A comfortable, flexible belt with built in electrodes is worn on the chest just below the bust line. An adjustable elastic strap holds the electrode belt in position against the chest. A transmitter, which attaches to the electrode belt or is built into it transmits the heart EKG signal to a receiver in the monitor unit. Advantages of the chest electrode EKG system are: 1. it is generally the most reliable and accurate system; 2. most people find that once the chest strap is on, it is less bothersome than a finger tip or ear lobe sensor; 3. they have convenient wristwatch style readouts and; 4. the largest number of different manufacturers and models are available with a wide variety of features. The disadvantages of this system are: 1. a little more time is usually required to put on the chest strap since it goes under the clothing directly onto the skin; 2. this type can be affected by interference from electromagnetic radiation from some motorized exercise equipment; close proximity to TVs and computers; high voltage power lines, etc., and; 3. since most of these units operate on the same frequency, if there are one or more other users in the same area each person’s monitor can be affected by another if the users are within about 2-1/2 feet of each other.

The preceding summarizes the basic characteristics of all heart rate monitors. Which one is best for any given individual is going to be determined by their own requirements and preferences, by the type of exercise they are planning, and their budget.