To monitor or not to monitor. The answer boils down to a basic question of your philosophy as a runner. Those who favor heart rate monitors (HRMs) will tell you that HRMs are a great way to hone the pace of any given workout to the precise intensity called for. These fans often report big performance improvements thanks to their HRM training. With an HRM, advocates say, you can always avoid overtraining; by exercising at a specific heart rate, there's no longer any guesswork, only the fact of hard numbers.
Those who pooh-pooh HRMs, on the other hand, like the guesswork. These folks prefer to have their pace governed by how they feel, rather than by an electronic gizmo strapped to their chest. To these purists, an HRM introduces a cold edge of technology and science into their running, cutting into the joy and freedom of their run.
It's simply a difference of outlook. If you're running mainly for performance and you want to squeeze the maximum conditioning out of each workout, you'd probably like an HRM. If you run mainly for fun and for release, you not only won't like an HRM, you'd probably resent it. It's up to you.
Training with a heart rate monitor
The idea behind training with heart rate monitors is to help you run at the level of effort you designate. Turns out that your heart rate is an excellent indicator of the efficiency with which your muscles are using oxygen. And this indicator is consistent over your lifetime. No matter how fit you become, a given range of heart rate will always indicate the same level of effort. As your conditioning improves, of course, it takes a harder workout that when you started running to match the same level of effort.
The HRM, in other words, can help you adjust your training program to account for your own improvement. Say you average a 9 minute mile for a five-mile workout with an average heart rate of 150 beats per minute. As you improve, your heart rate for the run will decrease if you keep that same pace, because it takes less effort. If you build your running around maintaining that 9-minute pace, you will eventually find that your workout no longer challenges your system. If you instead focus on maintaining that 150 beats-per-minute heart rate over time, you will continue to push your body and your average time per minute will decrease even as you put out the same level of effort.
The whole idea is to keep you pushing at the effort that will bring you the most gains. In general, this almost always means preventing you from pushing yourself too hard. Overtraining is a common mistake, since we runners are notoriously inaccurate in gauging our training effort. An HRM will tell you when you're straying outside the target zone of effort, helping you achieve a high level of fitness without straining too hard or winding up injured. While the device can also let you know when you're going too easy, most runners are surprised to find that they're usually running too fast.
Your maximum heart rate
In order to figure out what the little numbers on your HRM mean, you need to know your maximum heart rate (max) in beats per minute. Once your max has been determined, you can easily figure your target heart rates for a variety of workouts. The max is different for every individual and typically changes with age, but you can get a rough gauge with these (very) simple formulas:
Men: 220 minus your age.
Women: 226 minus your age.
If you are physically fit, add 10. That's your max in beats per minute.
For greater accuracy, or if you just have an aversion to subtraction, a stress test will take you close to your maximum heart rate. Or just find a long, steep hill and attack it hard until you can't possibly run faster, then sprint -- we're talking about-to-pass-out fast. At that point, check your heart rate for a fairly accurate reading of your max.