Among the (many, many) things you probably do not know about juggling is the fact that it is, at times, a physically grueling act. It's something I certainly failed to appreciate before meeting Alex Barron. We recently met at a squash court in Burbank, California so I could watch him practice his craft. There, the enclosed space shelters him from trajectory-wrecking winds, the high ceilings afford him ample space, and the white walls provide a uniform backdrop, ideal for passively tracking the movement of arcing objects—at times, a dozen or more of them.

At 23 years old, Barron is the world's best juggler of 10, 11, 12, 13, and 14 balls. His physique is statuesque: 6 foot 3, big shoulders, little joints, cover-model muscles. When he's not setting records in numbers juggling (the practice of juggling high numbers of objects), he surfs and rock climbs, but neither activity exhausts him quite like lobbing pellet-filled pouches high into the air. "The physicality of it I find quite hard," he says between heavy breaths, a puddle of sweat collecting at his feet. "Practicing high numbers two days in a row is just really rough on my body."

In October 2011, Barron became the first person to flash 13 balls on video (in a flash, the juggler throws N balls and executes N catches), a feat that revived longstanding debates over the absolute limit of numbers juggling. Practitioners often put the ceiling at 14, a number whose experimental origins can be traced to a paper published in 1997 by stuntman Jack Kalvan. A mechanical engineer and lifelong juggler, Kalvan devised a simple mechanism for measuring the speed and acceleration of jugglers' hands. From the data he collected, he concluded that someone would eventually juggle 13 balls—and while he never went so far as to claim an upper limit, he did write that "flashing 15 doesn't seem too unlikely."

The paper was controversial in juggling circles. Peter Bone, an accomplished numbers juggler and occasional competitor of Barron's, took issue with Kalvan's methods. "There are so many variables that aren't taken into account by simply measuring hand acceleration," he wrote on jugglingedge.com, in a thread about the empirical and anecdotal bases for a 14-ball threshold. "I think the 14 ball claim just comes from the experience of numbers jugglers in general. For example, Ben Beever [another premier numbers juggler] and I ... think that a 14 ball flash is possible, but not 15."

Bone wrote those words in December of 2012. Not six months later, Barron broke his own record by throwing and catching 13 balls 15 times. "I am working on [a 14 ball flash]," he wrote in the notes of the YouTube video he posted as proof, "but it may be a while."

It took him nearly four years. In April 2017, Barron became the first person to flash 14 balls on video. To appreciate everything that's going on, you'll want to watch this footage several times; it happens that fast:

An instant before liftoff, Barron dips into a shallow squat, loading his legs with the extra energy he'll need to loft the first ball into the air. Though the bean bags weigh just 70 grams apiece, it takes him as much effort to throw each one as it would to hurl the entire contents of his hand. The first toss, then, feels, to Barron's right hand, equivalent to lobbing 1.25 pounds high into the air. The second and third tosses: a hair over a pound each. The fourth and fifth: just under a pound apiece. Only on the 13th and 14th throws does propelling the bag feel like flinging a mere 2.5-ounce sack.