Seek details to pick perfect workout tool

What happens inside your body when you exercise is governed by a set of measurable reactions, and one good way to help yourself get in shape is to keep track of what's going on.

The technology to monitor and analyze workouts has become progressively more sophisticated, and priced across a broad range. For well under $100 you can get a brand-name heart-rate monitor; an investment of $300 to $400 will buy a training watch with software that lets you analyze and customize workouts.

With the gift-giving season under way, it seemed a good time to walk through some of the choices. Three of the main manufacturers, Polar, Garmin and Suunto, provided test units that included general fitness models and higher-end trainers. And that's just a taste of the range of products available.

Forethought and careful shopping are required to weed through the choices. All of the units offer many of the same basic functions: monitoring heart rate with the use of a chest strap, estimating calories used and allowing you to set goals to guide your workout.

Check some of the companies' Web sites to learn what's available and compare options.

Here are a few basic questions to ask about yourself or your intended gift recipient:

• Are you all heart?

If you want just a heart-rate monitor, major manufacturers such as Polar and Timex offer basic models for as little as $50 or $60. For about $150, Polar's new FT40 gives each user a "dividing line," based on heart rate, between his "fat-burning" and "fitness" zones.

This is a somewhat artificial distinction, related to how the body uses energy. For about $20 more, the Polar F11 provides a more sophisticated set of heart-rate training zones and will automatically construct a weekly program based on them. Both let you upload to an online journal that totals what you do and compares that with set goals.

• Do speed and distance matter?

If you want to keep track of how far and fast you go, you'll need a unit that is compatible with some sort of sensor. Look for package deals where the sensor is included with the watch. Garmin's Forerunner 405 comes with a GPS device built into the watch-size unit, an engineering marvel that includes a nifty iPod-style touch control around the outer bezel. At $300, it is pricey, but it makes for an easy, one-stop purchase. Keep in mind that GPS devices are only as good as their signal.

Polar has put its focus on improving the foot sensor and delivers a unit that will measure stride length and cadence, important if you are trying to improve your running style and speed. Bike units are sold separately by each company.

One tip: If you use a foot sensor, calibrate it to a known distance.

• Does GPS matter?

If you're trail-running to Grandma's house and want to make sure you get home - or want to save favorite routes and have access to directions during a workout - Garmin is the choice. The Polar and Suunto GPS units will track speed and distance, but the watches don't have the navigation features that Garmin offers.

One downside to the Garmin: It is an energy hog.

Comparable models, Polar's RS800 and Suunto's t6c (both about $400), have conventional, user-replaceable watch batteries, though their GPS units use a separate set of AAs.

• How geeky can you get?

All three companies offer software and online tools to upload data, analyze them and plan workouts while you're sitting at your computer. On this front, Polar's RS800 series and Suunto's t6c have stronger analytical tools than Garmin.

All three companies allow you to set up custom workouts including a warm-up time, a speed goal and a set of intervals. Polar has an online database of downloadable workouts (currently just a few but with plans to expand). Garmin offers a virtual partner, a little icon running buddy to pace yourself against.

• How connected do you like to be?

Garmin has nailed this category. Its uses a Bluetooth-like technology called ANT to automatically upload data from its watches. The same technology allows you to trade workouts with a friend. Suunto's higher-end t6c comes with a USB cord that clips onto the watch. Polar's RS800 uses an infrared-USB link that requires a few clicks to get rolling. Some of the models require you to buy a separate piece of gear to do the downloading.