A few years ago, Under Armour Inc. (UA) was still struggling to build its brand name; today, the company is preparing to go head-to-head with the likes of Nike (NKE) by moving beyond the sports clothing that helped win the loyalty of pro athletes and couch-bound sports fans and introducing a new electronic fitness monitoring device, the Armour39.

It isn’t as if Under Armour needed to venture into new territory in order to prove itself to investors. The company’s revenues have continued to climb, along with its earnings, as the company continues to expand its retail outlets in North America and open its first stores outside the continent. And neither analysts nor the company itself see that pace of growth as likely to slow any time soon: when it released its fourth quarter earnings (up 54% over year-earlier levels) Under Armour took the opportunity to say it expects that sales will grow another 20% to 21% this year. And if profit margins aren’t as wide as they have been in recent years, they remain north of 47%.

The company’s new product will face some tough competition from products that are already on the market and that also are designed to help athletes – pros or recreational users – monitor their progress and improve their performance. Most of the devices are designed to be worn on the wrist. While that is simpler for the user, the Armour39 may pick up a greater range of data simply because it’s a chest strap. It also is designed to function best during the wearer’s workout session, and to help the user adjust everything from the body position to the workout duration to improve results. All the data can be uploaded into the cloud or loaded onto an Apple device. (An Android app is pending.)

Under Armour’s shares aren’t cheap, trading at 41 times trailing 12-month earnings, but of late the PE ratio relative to the company’s growth in earnings has been trending downwards: a positive signal. A stock chart shows the shares giving ground of late. Certainly, Under Armour offers just as much upside potential as does another high-expectations stock, Lululemon Athletica (LULU). Adding the Armour39 to its product mix could make Under Armour the more appealing stock of the two, however; while Lululemon’s yoga pants may be stylish and flattering, they can’t tell you whether you need to do more reps or increase your heart rate. Lululemon makes apparel; Under Armour has reminded the market that it makes smart apparel, and that it has done so since its debut creating athletic shirts that helped wick perspiration away from the skin.