Tim Cook, Draymond Green face off in Apple Watch challenge

Green, a professional NBA player for the San Francisco Golden State Warriors, challenged Cook on Tuesday in a Twitter video. The Bay Area-based Apple chief executive promptly agreed to the competition.

Cook appeared to have a head start in the challenge with his morning workout on Monday. In a tweet, he asked if Green was up yet.

Green responded with an image of his own on Monday morning, showing that he hadn't had the productive start to the day that Cook had. The Apple CEO famously wakes up at 4 a.m. each morning.

A few hours later, Green seemingly caught up with Cook — and asked in a tweet if the Apple executive was still getting in some activity during the day.

Cook responded with an image of his shoes up on a table, and said he was "taking a break" so that Green could catch up.

In protest, Green said there was no need for Cook to "take it easy" on him.

The Apple Watch supports seven-day activity competitions between users as a way to motivate them to get active. It isn't clear if Cook and Green are, in fact, in a activity competition or if they're simply informally competing by posting images of their progress.