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

— -- 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.”