Inside Apple's Top Secret Health and Fitness Lab for Apple Watch Development

ABC News was given exclusive access to Apple's testing facility.

“[The employees] knew they were testing something, but they didn't know it was for the Apple Watch,” said Jeff Williams, Apple’s senior vice president of operations. “We hooked them up with all the masks and so forth, but we would put on an Apple Watch covered up.”

Apple Watch was first unveiled last September and it’s slated to be in stores next month. Ranging in price from $349 for the Apple Watch Sport to $17,000 for the 18-carat gold Apple Watch Edition, the watch contains a “health kit,” which can track everything from your heart rate, calories burned, distance walked and how much the user stands per day.

The lab, Blahnik said, also used “climate chambers,” to have fitness participants test the watch in different environments, and then they would actually have employees go to different places around the world.

Dr. Michael McConnell, a professor in cardiovascular medicine at Stanford Medicine who also directs Stanford's cardiovascular health innovation program, said Apple’s new health efforts that include ResearchKit will be a game changer in cardiovascular technology.

“We can use the power of something that they carry with them every day to help with measurements and surveys,” he said. “I think it is offering us a new way to do medical research.”

The more a user wears the Apple Watch, the more health data it can collect, and over time, Blahnik said that can be a powerful force in the fitness tech market.

“I think we've amassed already what may be one of the world's largest pieces of data on fitness,” he said. “Our view is, we're just beginning. We think there's a lot to this fitness thing...the impact on health could be profound.”