Fitbit shares run up 50% in 1st day of trading

Shares of Fitbit Inc., maker of a popular device to track physical activity, soared 50 per cent in their debut on New York markets on Thursday.

Fitbit's initial public offering the priced at $20 a share, valuing the company at about $4.1 billion US.

Fitbit makes devices that can be worn on the wrist or clipped to clothing to track steps taken, calories burned and hours spent sleeping. Users track their own progress through their smartphone.

There are other devices going after the same wearable technology market, including Jawbone, Fitbug and Apple watch, which may well become the biggest.

But Fitbit was early out of the gate and had sold 20.8 million devices as of March 31, making it the leader in the U.S. fitness activity tracker market, according to market research company the NPD Group.

With cash from its IPO, it plans to expand its sales network as well as work on new applications.

The company is facing two lawsuits launched by Jawbone accusing it of violating patents after a group of its former employees jumped ship to the rival company.

Fitbit sold a total of 22.4 million shares, raising $448 million. Its stockholders sold another 14.2 million shares, worth about $284 million.

The stock is trading on the New York Stock Exchange under the ticker symbol "FIT."