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For a field already glutted with gadgets, the Nike + iPod kit is the most elegant of high-tech runner's aids. An instrument the size of a pebble measures your pace from a pocket inside one of Nike's specially designed shoes. The pebble streams data to a computer that keeps time and calculates caloric burn. Instead of making you buy a whole new computerized accessory, Nike and Apple decided to use a computer you may already own, an iPod nano.

When you drop the pebble into your shoe and connect the wireless receiver to the nano, a Nike + iPod menu item appears. Click it, then select a distance or time for your workout. Select your music, a particular playlist or the iPod's "Shuffle Songs" feature. You are immediately prompted by a female voice to begin your run, and then the music adjusts to the right volume. The voice returns calling out your performance, at every 10-minute interval for instance, or every time you hit the nano's center button. As she speaks, the music falls to the background. Toward the end of your run, her calls increase in frequency, a countdown to your personal finish line. (If you want, you can change the woman's voice to a man's.) To get you going when you start to drag, you designate a Power Song, activating it mid-run by holding down the center button.

When your run is done, you dock the nano, automatically uploading the distance, time and caloric data to a server, where you can track your performance over days, weeks or months. You can even set distance, calorie or speed goals for yourself, and challenge others to races or tests of endurance.

What's freaky about the system is that there's no GPS tracking system or anything, just a little gyroscopically enabled pebble and the receiver clip for the nano. The pebble measures the impact of each footfall, and the acceleration between your steps to determine your distance. While the system is good at guesstimating distances, it's not perfect. When my wife and I tested it, it tended to say we went a tad farther than we really did. Serious runners should calibrate it to their stride. To do this, you go to a place where you know an exact distance (Apple suggests a school track), and follow simple instructions under the Calibrate menu item.

The pebble turns itself on and off automatically, and has an internal battery that will last about 1,000 hours — that's an hour a day for nearly three years. You can't replace the battery, but its replacement cost will be negligible, especially after that period.

My cardiovascular weapon of choice is the elliptical machine, but Apple says their system was built for runners. When tracked by Nike + iPod, the movements of the elliptical appear slow, and the stride appears short (because the machine's up-and-down motion is not taken into account, nor is its tension). Distance is measured about right, but the calorie count is way off. Since the product was announced, people have wondered what sorts of athletics they can use it for. For the time being, it's all about running.

The price of the product itself is $29, but there are some hidden costs you should know about. You can't wear just any shoes. Nike has already launched six lines for both men and women, priced from around $80: "Nike +" versions of existing shoe lines, with a hollow pocket for the pebble. The company plans to have more lines by the holidays, along with a selection of running clothes with built-in weather- and sweat-proof nano holsters. The nano itself costs between $149 to $249. If you don't own a nano, you could easily set yourself back around $300 for the whole system. Perhaps it takes this sort of financial investment, instead of a series of hollow promises, to get yourself onto the road of physical fitness.

• WILSON ROTHMAN
• Apple and the sports giant team up to create a new running system