Under Armour now owns the world's largest digital health and fitness community.

With Under Armour's acquisition of health app MyFitnessPal ($475 million) and social fitness network Endomondo ($85 million), the apparel company is now sitting on a massive audience of connected health enthusiasts.

While we don't yet know exactly what UA will do with this new connected community, it's clear that the pursuit of better health has never been so technologically empowered. Here are a few reasons marketers should care about the acquisition.

1. Community building is now a core business responsibility.

Buying MyFitnessPal wasn't just about buying a tool that counts calories-it's much bigger than that. Nowadays, successful businesses are building and growing proprietary communities that allow people to connect over shared interests and passions. These people aren't limited to customers; they're also prospects, fans of competitive products, and everyone in between. MyFitnessPal and Endomondo both have dedicated daily users who rely on the app to keep them accountable for their health. Now, I expect we'll see a community-centric approach take center stage within these services.

This type of digital community-building should perk up marketers' ears because this responsibility will naturally fall to many marketers' plates. Marketers already oversee social networks, blog communities, email subscribers, and many other core communities within their companies. Building active, engaged communities is about connecting, not selling.

2. Mobile apps aren't just for traditional tech companies.

Under Armour is about as far from a tech company as you can get-they make clothing. But with this acquisition, they're a full-fledged tech company because they own and manage a huge digital audience. They're also responsible for tech support and troubleshooting issues that could transpire on MyFitnessPal or Endomondo's digital properties.

If apparel company Under Armour is so worried about reaching mobile customers that they'll spend $475 million on it, you should be worried about it, too. Every company should be considering how to make their online presence more mobile-accessible and seamless. An app is one important tool that many companies are adopting to accomplish that, but there are plenty of other ways that marketers can excel at mobile-first content: mobile-optimized emails, websites, and landing pages, for starters. For any marketers who have been falling behind on a mobile content strategy, this acquisition should be a wake-up call.

3. Social communities beyond Facebook and Twitter are breaking through.

Beyond Facebook, Twitter, LinkedIn, YouTube, and the other top social networks, we're seeing niche networks crop up in a variety of industries. Health and fitness is a major player in the niche social network landscape, with communities like Endomondo and Fitocracy claiming big pieces of the marketshare. But there are important smaller communities, too, like those that crop up on forums.

Social listening can't be limited to the big social networks alone. Marketers need to be listening and responding to customer comments and complaints all over the web, whether that's a question on Quora or a complaint on a personal blog. All web properties are increasingly social, thanks to the proliferation of comment fields and our desire to share content. Marketers must broaden their social strategy to include a more holistic view of all customers, not just those on Facebook or Twitter.

As a user of MyFitnessPal myself, I'm interested in seeing where Under Armour takes the community and how they inspire fitness enthusiasts to take their health to the next level. As marketers, we should also be interested in how this apparel company makes the transition to a multi-platform digital publisher and community owner.