Watch the Watch

New wrist-mounted lifestyle and activity monitors not only tell you the time

A wrist watch used to do one thing. It told the time. Now there’s a new generation of wrist-mounted devices that make the word “watch” seem inadequate. These wrist-mounted lifestyle and activity monitors not only tell you the time, they can give you exercise statistics like mileage, body temperature, and location by GPS. Some can even calculate your current heart rate – and here’s where the  benefits and the trouble come in.

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There are some people for whom exercise is a risky proposition. They may have heart conditions that  require them to exercise within a prescribed target heart rate.  The benefit is that heart rate monitor watches make it easier for people to keep an eye on their target heart rate.  They can either watch the watch – or in some models, pre-program in the target heart rate and a warning will sound if the person goes over their heart rate.  The danger  comes with exercisers who need to be monitored .  These  exercisers might overestimate the reliability of their wrist-mounted device as an indicator of normal or abnormal heart rhythm.

“These devices are not sophisticated enough to reliably detect arrhythmias or rhythm changes,” says Gordon Blackburn, PhD, Program Director of Cardiac Rehabilitation.   In addition – the watch is only as good as the contact you provide it.  Heart rate can be “miscounted” if the watch has poor contact with the skin , or if you do not have adequate moisture on the electrodes.  Dr. Blackburn says, ” if the heart rate reads too high, a person may decrease their effort to level where he or she may not gain benefit, but if it reads too low, the person may push too hard trying to elevate HR reading. ”

The usefulness of these devices as monitors of your physical well being is also limited by a lack of context. It’s not enough to know how fast you are driving to avoid a ticket, for instance. You also need to know the speed limit. So it is with heart rate, which needs to be interpreted in light of your age, health,  medications, and exercise history.   Your doctor can provide you with a heart rate range that is appropriate for your medical condition; or if you want to be more precise, you can get a complete exercise prescription after a stress test.

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While data is good, the best way to monitor your exercise well-being is to be aware of your physical sensations. In other words, watch the watch, but “listen” to your body.

“For heart patients, or anyone, it is important to pay attention to how the body feels during activity,” says Dr. Blackburn. “If you sense anything questionable or unusual, get in touch with your doctor.”

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