This is not your father's pedometer

Accelerometers and GPS allow runners to measure their running distance (and speed) in real time with excellent accuracy
My dad rode the wave of the 1970s running boom. Back then he used a pedometer -- a small mechanical device that looked something like a compass and was worn hooked to one's waistband -- to measure the distance of his runs. It was absurdly inaccurate. The same course that came out to three miles when he used it measured 2.5 miles when I wore it.

How times have changed. Two advanced technologies -- namely, accelerometers and global positioning systems (GPS) -- now allow runners to measure their running distance (and speed) in real time with excellent accuracy.


The FitSense FS-1 and a pair of Nike products, the SDM Triax 100 and the SDM Tailwind, use accelerometers to measure distance, speed and pace. Polar, known for their state-of-the-art heart rate monitors, has recently launched the 625X running computer that also uses acceleromoter technology with integrated heart rate.

An accelerometer is a device that measures changes in the rate of linear movement. Unlike pedometers, which merely count steps and can't account for variability in stride length, accelerometer-based devices contain sensors that you attach to the laces of your shoe and make several hundred measurements per second.

The FS-1 arrives at 98 percent accurate distance measurements by monitoring both stride rate and ground contact time of the foot. The Nike devices measure the acceleration and deceleration of your shoe and are said to be 97 percent accurate. is looking forward to testing the Polar 625X's accuracy and reliability in an upcoming product review.

Ninety-seven percent is not bad, but in an exacting sport like running it's not great, either. For example, 97-percent accuracy for a 26.2-mile marathon comes out to either 25.4 or 27.0 miles.

If you used one of these devices to control your pacing while attempting a marathon personal record, you might go just a bit too fast and bonk in the last 5K. Or you might think you're on pace all the way through only to find out at the finish line that you actually ran a couple of minutes too slow.

The best use for this device is to measure the approximate distance of recovery, foundation and long training runs.

GPS units

The accuracy of the GPS-based Timex Speed and Distance System and Garmin Forerunner puts that of the accelerometer-based units to shame. Using the same technology that satellite-guided missiles use, these devices are about as accurate as a car's odometer and speedometer.

The disadvantage of these products is that trees, clouds and other obstructions can interfere with their ability to communicate with the satellites upon which their functioning is completely dependent. But as long as such obstructions are absent, these devices are accurate enough to allow you to do precisely measured workouts of all formats -- even intervals -- away from the track.

The problem of loss of satellite contact with GPS-based speed and distance devices appears to be shrinking, however. It was a major source of frustration with the first-generation Timex Speed + Distance unit that I owned, but my new Garmin Forerunner 301 has only let me down a couple of times in the several months that I've owned it.

One of the best uses for the new speed and distance devices is controlling your workout intensity by pace (minutes per mile). Many runners use heart rate to control their workout intensity, but using pace instead of, or in combination with, heart rate is better. The reason is that pace is a measurement of performance, whereas heart rate is not, and the goal of training is to improve performance.

As celebrated endurance coach Joe Friel says, "In a race they don't ask who got the highest heart rate -- they ask who got to the finish line first."

Recently, I teamed up with Training Peaks to develop a pace-based training system that takes advantage of the new speed and distance technologies.

Specifically, we created something called the Pace Zone Index (PZITM), a table that, when used in conjunction with a GPS device, helps runners of every fitness level do each of their running workouts at just the right intensity level.

In addition, I designed a set of 5K and 10K training plans (with plans for longer races to come) that are completely based on the PZI system. By determining your current PZI and selecting the right level of 5K or 10K training plan, you can train in the most customized and precise way possible, virtually eliminating waste and error from your program. To find out more about the Pace Zone Index, go to

The FitSense FS-1, the Nike SDM Triax 100, and the Timex Speed and Distance System are sold in versions that come with and without an integrated heart rate monitor. Prices range between $99 for the Nike SDM Tailwind and $300 for the Nike SDM Triax Elite, which includes a heart rate monitor. The Garmin Forerunner retails for $160 and comes in only one version without a heart rate monitor. All of these devices can be purchased online and at select running specialty shops.

This article was adapted by the author from The Cutting-Edge Runner: How to Use the Latest Science and Technology to Run Longer, Stronger, and Faster (Rodale, $15.95). Click here to purchase a copy.

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