A billion dollar sports brand just stepped up its digital health game in a big way.

Baltimore, Maryland-based athletics apparel company Under Armour is acquiring Austin, Texas-based MapMyFitness for a reported $150 million. MapMyFitness, which has about 20 million registered users now -- up from 13 million in January -- offers running, biking, and walking apps and social networks that integrate with a wide array of other digital health apps and some 400 devices. The company's GPS-enabled apps, which first launched for Android users in 2007, help users map, record and share their workouts with others on the platform.

MapMyFitness has raised more than $20 million from investors that include Austin Ventures and Milestone Venture Partners. Worth noting that Under Armour expects to rake in north of $2 billion in net revenue this year, so the $150 million pricetag, while impressive when compared to other digital health acquisitions, is a drop in the bucket for the company.

In order to find its place on Inc. Magazine's fastest growing company list of 2012, MapMyFitness disclosed to the publication that its revenues in 2011 were $6.2 million, up from about $500,000 in 2008. Around that time -- early 2012 -- the company had half as many employees as it has today -- just 53.

Under Armour's digital health moves have been relatively meager to date. The company partnered with Zephyr Technology to power a health sensor-laden shirt, called E39, which was famously used in the NFL Combine in 2011. Under Armour uses other technology to power its smart shirts now. Under Armour also has a couple of fitness apps on the market including a healthy challenges app called What's Beautiful and an app called Armour39, which connects wearer's smartphones to their Armour39 wearable device.

Here's how the company describes its Armour39 app in Apple's AppStore: The app "monitors your workout by tracking your heart rate, calorie burn, real-time intensity, and WILLpower, Under Armour's unique measure that reflects overall workout difficulty in a single score. The Armour39 app is compatible with any Bluetooth Smart Heart Rate monitor, although optimized for use with Under Armour's Armour39 Strap and Module."

Under Armour CEO Kevin Plank told the Wall Street Journal this morning that the MapMyFitness buy is not the start of an acquisition spree. Plank says his company began courting MapMyFitness in August -- which was just a few months after it raised an additional $5 million -- and that the acquisition is Under Armour's first. MapMyFitness will stay in Austin as an Under Armour subsidiary, he said.

Over the years MapMyFitness has grown to become a high profile fitness app and community company and it has appeared in coveted Apple advertising spreads in various mainstream publications. Its acquisition is one of the landmark deals of 2013, which include earlier acquisitions like Jawbone's BodyMedia buy in April.

MobiHealthNews will keep you posted with more details on the MapMyFitness acquisition as they unfold over the coming days.