You can always measure your heart rate the old fashioned way by putting a finger to your wrist or neck (count for 10 seconds and multiply by 6 for beats per minute), but you usually have to stop your activity to take your pulse.

Another option is using a heart rate monitor which consists of two parts: the monitor strap that's worn around the chest (some sports bras hold a monitor in the bottom across the front) and a heart-rate signal that looks like a digital wristwatch. This wrist signal device displays your heart rate at the moment in beats per minute, along with additional information you might need.

Heart rate monitors can offer a variety of functions, but not all might be necessary for you. And considering that the cost of monitors can start at $75, you'll want only the functions you need.

Here is a prioritized list of heart rate monitor features, but keep in mind that Mark Fenton feels only the first two are essential:

1. Stopwatch feature. It's convenient to be able to glance at both your heart rate and your exercise time on one device.
2. Set a target rate, with alarm. This allows you to enter the upper and lower limits for your target heart rate (see below). On some models, you can set both a visual signal (light) and an audible one (beep) when you go out of range.
3. Accumulated time in and out of range. If you want to know exactly how much time you spent in target range, you'll need this feature.
4. Memory. Some monitors just recall your workout time and how much time you spent in target range. Others can play back your minute-by-minute measurements, so that you can see, for example, how your heart rate climbed during each speedy interval and dropped as you eased up to recover.
5. Download to a computer. Some manufacturers offer interface cables and software so you can download a detailed playback of your workout on your computer and enter it into your digital training log.