In nearly a decade of competitive freediving, 34-year-old set 11 South African records, including a dive in the Red Sea to 207 feet on one breath. She did it through mental training and a strict regimen of chest stretches that increased her lung capacity from four to six liters. Now she’s teaching her hard-earned lessons to athletes from a range of backgrounds, from big-wave surfers like Greg Long—who need to endure crushing hold-downs after wiping out—to rugby players and cyclists looking to gain a competitive aerobic edge. Ultramarathoner Ryan Sandes credits Prinsloo’s training with helping his body use oxygen more efficiently. “Even if it makes me only 2 percent better,” Sandes says, “it’s worth it.”
In her courses, Prinsloo focuses on yoga-like poses and breathing techniques (See the sidebar). The results, she says, are as effective as any performance-enhancement procedure. “You don’t have to inject a cup of your own blood,” she says. “There are other, legal reserves you can tap into.”