(Pocket-lint) - Apple first began making Apple Watch more than four years ago, but it's only now been revealed that part of the company's development process apparently included building a gym-like lab for gathering fitness data and testing tracking features.

ABC News got a behind-the-scenes look at Apple's hidden facility and even posted an exclusive video showing Apple employees working out with various equipment. Many can be seen donning sensor-tracking technology used for understanding how the body reacts during specific exercises and in certain conditions. The lab even has simulated-climate chambers, and all the collected data goes toward developing Apple Watch.

It appears as though any employ from the company, including engineers and managers and developers, can volunteer to participate in tests, which Apple started conducting two years ago, though it didn't reveal to employees the reasons why they were being tested until recently. In the video, you can see them running on treadmills, rowing, doing yoga, and wearing masks to measure their breathing changes.

Apple executives Jeff Williams and Jay Blahnik were on-hand to give ABC a tour: “[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, during the recorded interview. “We hooked them up with all the masks and so forth, but we would put on an Apple Watch covered up.”

Despite having this secret gym for testing, Apple still insisted on visiting different locations around the globe in order to conduct more in-depth tests for its upcoming, health-focused wrist wearable in a variety of extreme environments: “We have traveled to Alaska and gone to Dubai to really test Apple Watch in all those environments,” said Jay Blahnik, Apple's director of fitness and health technologies.

Blahnik also claimed Apple has amassed what may be one of the world's largest pieces of data on fitness. The company believes there's still a lot more to be done in regards to fitness, and that the impact on health could be profound.

Watch the video above for more details. It premiered on Good Morning America but is part of a larger segment airing tonight.

UPDATE: It looks like the video was pulled, but we've added a gallery of screenshots.

Writing by Elyse Betters.