An HRM's wristwatch-style receiver gives you real-time data on your workout's efficiency. Most models provide average heart rate, as well as the high, low and target heart rate reached during your workout.
Basic models offer up to 3 target zones; advanced models have from 3 to 6 target zones. With the capacity for multiple target zones, you can preprogram your heart rate monitor for a series of different workouts (e.g., endurance, aerobic and anaerobic variations described above). If your HRM offers only a single aerobic target zone, you'll need to reprogram it every time you want to change the exercise parameters.
Other features to consider when shopping:
- Sport watch: Includes features such as a countdown timer, calendar and clock.
- Stopwatch and lap/split times: After each lap at a track or every mile on a marked-distance race course, hit the "Lap" button to see how your pace has changed throughout your workout or race (a.k.a. your "split").
- Recovery heart rate mode: Tracks the time it takes your heart to return to its normal, resting rate. It's a good indicator of cardiovascular fitness and especially important if your workouts include sprints or interval training.
- Time in target zone: Tracks the time you spend exercising within your target zone. Some zones and goals require more time than others.
- Calorie counter: Estimates the calories burned during exercise. This can be especially handy if your workouts are part of a weight-loss program.
- Speed and distance monitor: Calculates the speed and measures the distance covered in a particular workout. This is typically done via a GPS receiver for outdoor use or a foot pod for indoor use or use in an outdoor area with limited satellite reception. A foot pod uses an accelerometer to determine the length of each stride. For details, see the REI Expert Advice article, Speed and Distance Monitors.
- PC interface: Connects your heart rate monitor to your home computer so you can download training statistics for analysis and storage. This may be wireless or require a separate computer connection.
- Fitness trainer: This provides alerts for intensity levels that fall above or below your chosen training zones.
- Coded transmitter: Encrypts transmissions from the chest strap to the wristwatch-style receiver to prevent crosstalk, which are signals from the wireless HRMs of others exercising around you.
- Bicycle-mounting options: Many HRMs can dock to a bicycle's handlebar, though doing so may require a mounting accessory. Add a speed and cadence sensor to your bike to help maintain your cycling rhythm.
- Battery replacement: Many, but not all, HRM wrist receivers use consumer-replaceable batteries to simplify maintenance.