Apple has been using its own employees to test out the Apple Watch's health and fitness features for almost two years. And recently, ABC's Good Morning America got a tour of the secret workout lab, where Apple fitted internal volunteers with sensors "worth millions of dollars" (and some scary looking masks) to amass a ton of data on exercise and physical activity.

In many ways, it looks like your typical gym, with rowing machines, treadmills, and plenty of yoga mats. But from the beginning, Apple has been collecting all of this activity to help develop and improve Apple Watch. True to Apple's famous obsession with secrecy, the employees weren't told what project they were contributing to — though we have to imagine it wasn't difficult to guess it related to some sort of wearable.

ABC's tour was led by Jay Blahnik — one of Apple's earliest big fitness hires — who showed off "climate chambers" that help recreate workouts in extreme temperature conditions and varying humidities. Apple also visited locations across the globe (Alaska and Dubai are named) for proper outdoor testing. "I think we've amassed already what may be one of the world's largest pieces of data on fitness, and our view is we're just beginning," said senior Apple executive Jeff Williams, who appeared at the company's Apple Watch event earlier this month. Apple's executives have repeatedly said that the device could have a profound impact on personal health.

But it remains to be seen whether Apple Watch will outperform other fitness bands when it comes to tracking your heart rate and overall activity. Heart rate monitoring in particular is an area where wrist-worn products like the Microsoft Band, Fitbit Surge, and others have proven imperfect; devices strapped directly to the chest are typically far more reliable. Can Apple's sensors make a difference? We're looking forward to seeing for ourselves in a few short weeks. Apple Watch will be released on April 24th.