Chris Sharma, the 24-year-old monkey boy who in 2001 introduced the world to 5.15 climbing (the sport’s hardest grade), recently cobbled together a new boulder problem, across the roof of an Ozarks cave, that some say is one of the hardest lines ever completed. While roped climbers strive for endurance on 200-foot-long routes, boulder hounds use Herculean bursts of power to battle tiny, awkward holds over short stretches of rock. To solve Witness the Fitness, a 40-foot-long upside-down jaunt peppered with mushroomlike dollops of iron-hardened sandstone, Sharma had to hold himself parallel to the ground using three fingers in a shallow pocket and a toe hooked on a peanut-size nub. “It was one of the most impressive things I’ve ever seen,” says Josh Lowell, whose film company, Big Up Productions, captured the March 13 feat just outside Jasper, Arkansas, and has footage online at www.bigupproductions.com. Sharma won’t grade his prize—he never does—but says it’s the hardest he’s ever done, which suggests a V15, today’s limit for bouldering.