Athletic heart monitors have existed for several years now, but it wasn't until relatively recently that the technology behind them, and the development of heart monitor training techniques came together to make training with a monitor both simple and effective for the average runner. While many runners own heart monitors, often they may not be using the devices to their full potential. Other runners do not own a heart monitor and are unaware of the benefits of training with one.
Why Use a Heart Rate Monitor?
Heart monitors are devices that are designed for wear during strenuous exercise, and serve the purpose of measuring and recording your heart rate, while giving you instant feedback about the work level of your heart. The fitness of the heart is the key to one's aerobic endurance - sometimes called 'cardiovascular respiratory endurance'. Both for health and racing reasons, aerobic endurance is a point of focus for almost any runner. Heart monitors are one of the most effective aids for tracking and developing your progress on the path to increased aerobic endurance.
1) Accuracy And Ease: Heart monitors are the only effective way to track and record your heart rate over the course of an entire workout. Not only do heart monitors provide you with a complete record of your heart rate for the duration of your workout, but they are also more accurate than manual methods. Stopping during a run to count your pulse disrupts both your workout and your heart rate, and even the application of pressure to the carotid artery - perhaps the most common point for manual pulse detection - slows down the pulse.
2) Monitor Your Fitness: Cardiovascular fitness is the single most significant factor in your speed as a runner. Consequently, being able to track your cardiovascular fitness - not to mention tailoring your workouts to meet cardiovascular goals - is an extremely useful training tool. Measuring the work-rate of the heart is the most accurate method of determining how much benefit you are deriving from your workout (a discussion on how to gauge results can be seen in section III). Other methods, such as how hard one is breathing, or how tired one feels, can reflect other factors and give imprecise impressions of the effectiveness of your workout.
3) Prevent Over-Training: For many competitive runners, every week's workout regimen is essentially a seven-day dance along the fine line between optimal training and over-training. Using a heart monitor to avoid stressing your body too much means that you will maximize the efficiency of your training, while minimizing the opportunity for injury. Injuries are much less likely to occur when you are not over-taxing your body, and avoiding injuries is tantamount to avoiding setbacks in your training. While opinions differ on how much running is too much (we will discuss this more later), once you determine the desired intensity of your weekly workouts, you can use the monitor as a gauge. Are your recovery days really allowing your body to recover? The surprising answer, in many cases, is that runners' easy days are simply not easy enough. Use your monitor to stay below a certain ceiling, and you will avoid depleting your body's glycogen stores, ensuring that you will have the energy to perform your intense workouts with vigor and that you will not have to take unexpected days off from fatigue.
4) Prevent Under-Training: Though perhaps less common than over-training, some runners simply do not run hard enough, often enough. In this case, the monitor can function as a sort of coach, telling you when your body can handle more, and consequently, when you should pick up the pace. Set a minimum heart-rate goal for your run, and the monitor will sound an alarm when you have dropped below your target, telling you to work harder.
5) Pacing During Training: Perhaps the most obvious use for a heart monitor is to pace your training runs. Sometimes your time is not the best measure of how hard you are working. Different terrain, different energy levels, inconsistent distance measurements, and any number of factors can mislead you into thinking that you have performed well or poorly when the opposite may be true. Your cardiovascular performance is best measured by the work-rate of your heart, so pacing your training runs according to your heart rate is the best method of targeting your cardiovascular fitness as you do your workout.
6) Pacing During A Race: Some runners not only train with a heart monitor, but race with one as well. The monitor is a better tool for gauging effort during a race than mile markers, as the appropriate speed of each mile during a race can vary. Also, the monitor is indifferent to the wind, the paces of the other runners, the cheering of the crowds, the silence of lonely stretches that occur towards the end of some races, and any hills and curves; it is an objective observer than can help you maintain a consistent work rate, both over varied terrain and in areas where external factors affect your motivation and speed. Within a racing context, a monitor is perhaps most useful in preventing you from going out too fast or working too hard early in the race.
7) Enjoyment: While many runners enjoy their long runs, using a heart monitor adds a twist to running, whether it is being worn for a race or for training, for one mile or for twenty. Monitors can give you an accurate and fun way to quantify your progress, and if for no other reason, contribute some variety to the activity.
I need to get back in shape. 
Didn't help I was running like 20 psi 
