A heart rate monitor is a very accurate guide to how strenuous an overall workout is. A HRM isn't perfect, though. For example, you may work exceedingly hard to go charging up a short hill. At the top of the hill, despite the fact you are breathing deeply and your legs are burning, you may find your HRM showing a very low pulse. This is because it takes a while for your heart to catch up with your increased level of exertion. Likewise, at the end of a long period of exertion, your heart will still be pounding even when you are finished. (In these cases, a power meter is much more accurate. However, power meters are exceedingly expensive.) On average, a HRM will give you a good indication of your workout.
A calorie counter that uses either your heart rate or power output (along with your age, gender and weight) will give you a decent idea of how strenuous your workout is. However, as others have pointed out, a calorie counter that just looks at speed and distance is not going to be very accurate or helpful.
You really need to do some thinking about how you want to use an HRM before buying one. Some of the things to consider are:
- do you only want an HRM for cycling or do you run, kayak, skip rope, etc? If only for the bike, you may want a handlebar unit. Otherwise, you will want a wristwatch type unit.
- if you use it only on the bike, you may want one that is both a cyclocomputer and HRM.
- do you want to use it on one bike or multiple bikes? For one bike you may want a handlebar mounted unit. Otherwise, you may want a wristwatch type unit or one that you can buy multiple mounts for. (If wheel sizes are different, though, and you want to use it as a cyclocomputer it must
handle multiple bikes.)
- do you want to be able to download data to your computer? An HRM with a computer interface is much more expensive.
- do you want altitude, and GPS along with HRM? Now you are talking real expensive.
Anyhow, while it is interesting to know how hard you worked out, to effectivly use a HRM in training, you need to read something like: "The Cyclist's Training Bible" by Joe Friel. Joe Friel is a top notch trainer and in this book he lays out the theory and practice of conditioning and using a HRM. (Here is a tip: for best conditioning, you don't need or want to go full out all the time.)
Hope this helps.