Back in 2013, I was living in Palo Alto, California. That spring, circled on my calendar, was a track meet at nearby Stanford University, the Payton Jordan Invitational, about a mile and a half from our house. I wanted to be there because it’s a great meet for fans of long distance track racing. The weather is typically cool, and just three years before at the same meet, Chris Solinsky was set an American record in the 10,000 (a feature race at Payton Jordan) with a a 26:59.60.

The main reason I was there was for the triathlon component of the night. In the second heat of the 10,000 was none other than Great Britain’s Alistair Brownlee. Less than a year before in the London Olympics, Brownlee had won the gold in triathlon, and now he was racing against a cohort of national-class running specialists.

If you watch and listen go the Flo Track video of the race here,  you’ll catch a bit of conversation between the announcers talking about the differing race predictions in discussion boards, track geeks (letsrun.com) versus tri geeks (slowtwitch.com). The former apparently predicted a time around 30 flat and the latter suggesting he’d go under 28.

Brownlee had just come off running 13:57 at the Mount Sac Relays, another dream meet for distance runners, a time that allowed the  announcers to surmise that he would probably split the the difference.

It was a terrific 10,000 to run, and one in which a fan can see how Brownlee ticks and why he so solidly defended his Olympic gold title last week. Taking the lead with six laps to go, Brownlee’s facial expression was that of someone having a finger cauterized. A level of discomfort just this side of bearable. Yet he took the lead and pushed the pace.

In the final lap, Brownlee bolted to the front again, trying to get a break on Jose Marin and Zachary Hine. Hine was dropped but Marin fought his way back to Brownlee’s shoulder. Brownlee made Marin pay, holding him off into the turn. It was a classic track 10k sufferfest. Marin won the heat in 28:30 an Brownlee finished second, Brownlee snatching a PR with a time of 28:32. After the finish, while a volunteer stood nearby with a round of Gatorades, Brownlee laid on the track, his chest heaving. That he could push himself so hard just a half year after claiming his gold medal was insightful.

This wasn’t just physical discomfort. Brownlee’s mastery of Olympic triathlon has come because he isn’t tied down by an oversized ego. He was willing, if not eager, to test himself in a domain where he was certainly going to get beat. Athletes of all kind, even fitness junkies at the YMCA, can have a tendency to do the exercises or training that they are best at and avoid weaknesses. Obviously, Brownlee’s run was not a weakness in a triathlon race. So he sought out an arena where he was going to be pressed to the wall of his capacity.

“Alistair is the toughest athlete I know,” 2000 gold medalist Simon Whitfield told me over the phone.

So what’s next? As Brownlee once told the BBC, he wants to go longer: “I’ve done triathlon since I was 8 or 9 years old and always followed it and love watching all different types of triathlon. The Olympics were very much my passion and my dream since I was very young and I achieved that in London and want to try and do it again in Rio but after that I definitely want to have a change and try some longer distance racing as a new challenge.”

Watching Brownlee’s other-worldly pain tolerance, and knowing he’s been at the sport of triathlon since he was a third-grader or so, is exciting. What could this guy unleash? It also presents a key challenge. No stranger to injuries, the most important thing for Brownlee will not be in how hard he trains—he’s going to have that covered—but in making sure he doesn’t destroy himself. If he finds the sweet spot in transitioning to the longer distances, there’s going to be some fireworks.