Kleiner Perkins Caufield & Byers made an undisclosed seed investment in mobile fitness app developer WorkSmart Labs, according to a report over at AllThingsD. The investment was made through the firm's iFund, which was established in 2008 with $100 million to make investments in iPhone app developers. In 2010 the fund doubled in size to prep for the then-imminent launch of the iPad. AllThingsD reports that the iFund was impressed by the ex-Googlers on WorkSmart's team.

As AllThingsD points out, to date, WorkSmart Labs has only created Android fitness apps, however, the company reportedly submitted an iPhone fitness app to Apple this week. As of this morning, it's still awaiting approval.

WorkSmart Lab's apps are among a precious few health and fitness apps that have millions of users -- the company's apps have clocked 6 million downloads to date, up from 4 million in January. Other apps in the millions of users group include Nike+, LoseIt!, RunKeeper, and Endomondo.

At an event in New York City earlier this week, WorkSmart Labs CTO and co-founder Artem Petakov said that more than 150,000 of its apps' users post data directly to Facebook from their apps, and each posts typically has two or more comments of encouragement.

Here's how WorkSmart describes their apps: "Our mobile applications let you follow a personalized weight loss plan, schedule workouts, record them with your smartphone, track your eating habits, and more." The developer's app titles include: Noom Weight Loss, CardioTrainer, Calorific, CardioTrainer Pro, Race Against Yourself, and Cardio Entertainment.

For more on the round of funding, read this report over at AllThingsD