Men’s Health got a behind the scenes look at the fitness lab where Apple fine-tunes the Apple Watch algorithms that track your health and fitness. Like so many things Apple does, the numbers are staggering. According to Jay Blahnik, Apple’s director of fitness for health technologies:

‘Our lab has collected more data on activity and exercise than any other human performance study in history…. Over the past five years, we’ve logged 33,000 sessions with over 66,000 hours of data, involving more than 10,000 unique participants.’ A typical clinical trial enrolls fewer than a hundred participants.

Men’s Health also takes a look at the motivational messages coming to watchOS 4 and talked to Blahnik about the thinking behind the feature:

“We wanted to really make it easier for people to encourage each other, as well as smack-talk when the moment calls for it,” says Blahnik. “That’s why we have phrases like ‘Shazam’ and ‘You’re on fire.’ I share my activity with about 20 people, and whenever I see what someone else has done, it spurs me to train a little harder. It’s also a fun way to stay in touch.”

The refinements that Apple has made to watchOS 4 seem minor in print, but having tried the beta for about a month, I’ve been pleasantly surprised at the impact they’ve had, especially with respect to the fitness features of the Watch. Now more than ever, it feels like Apple has figured out what the Watch does best and is putting all its wood behind those arrows.