 -- Apple, known for keeping its product developments under the strictest of lock-and-key, gave ABC News exclusive access into its top secret health and fitness lab, where only Apple employees became test subjects for the new Apple Watch.

Apple engineers, managers and developers have been secretly volunteering for the past year in this state-of-the-art lab to participate in rowing, running, yoga and many more fitness activities in order to collect data for the Apple Watch’s inner workings.

“[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.

“We have traveled to Alaska and gone to Dubai to really test Apple Watch in all those environments, but we also wanted to be able to have a controlled environment here where we could see those extremes,” he said.

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.”