Wait, When Did Mark Zuckerberg Go Rambo?

For Mr. Zuckerberg, who has absorbed a number of metaphorical body blows over the past several years — including an election meddling scandal, a ghost town metaverse and widespread layoffs — it is perhaps a revealing time to start fighting back.

Mr. Zuckerberg is, of course, not the first tech titan to add significant amounts of muscle. Jeff Bezos, the Amazon founder and chairman, has, in his 50s, developed remarkable biceps, linebacker shoulders and impressive vascularity. But some of Mr. Zuckerberg’s friends say the new regimen is not exactly a surprise.

Though Mr. Zuckerberg entered the popular imagination as an indoor cat — the millennial archnerd outsmarting the strapping regatta princes of Harvard — the 39-year-old has been devoted to physical activity for much of his life. He was the captain of his prep school fencing team and became an avid runner in the 2010s.

According to Mr. Lessin, Mr. Zuckerberg goes through phases with new sports, including roller hockey and surfing, a hobby that was immortalized in an image of the magnate afloat in Hawaii, a haunting mask of sunscreen slathered on his face.

“He sees them as super-fun side quests,” Mr. Lessin said.

Famously competitive, Mr. Zuckerberg is the “great physical instigator” of his friend group, Mr. Lessin said, and frequently proposes physical challenges. “We’ve been on trips where he’ll say, like, ‘I’ll race you up that mountain.’” And on Mr. Rogan’s podcast, Mr. Zuckerberg said that he had successfully encouraged many of his friends to train in Brazilian jujitsu with him.

Perhaps unsurprisingly, Mr. Zuckerberg has a passion for benchmarking. In April, he posted a photo of a stopwatch appearing to confirm that he had run five kilometers in under 20 minutes. And though many commenters were skeptical of his Murph Challenge time, Mr. Zuckerberg clarified that he had done a special, easier-but-still-painful version, in which the exercises are performed in circuits.

Also performing a modified version of the Murph challenge: Two of Mr. Zuckerberg’s three daughters. He posted a picture of the girls mid-push-up, in the midst of a “quarter-Murph (unweighted)” — a clarification that the children were not wearing flak jackets.