There are risks. You could rupture an eardrum. You could squeeze—quite painfully—any of the airspaces in your body, some you didn’t even know you had. And you could black out.

There are about five different ways to black out—low oxygen, high carbon dioxide, loss of blood pressure and others—but they all have the same result. You might not feel it coming; one minute you’re ascending, grooving on the cerulean hues of the sea, the next, bam! Slumbersville. But the danger from blackout itself is exaggerated. “I’ve had maybe twelve blackouts,” Mandy says, “all on record attempts. But I was well cared for. In a few seconds I came around, disappointed that I didn’t make it.”

While a severe blackout can be spectacularly scary to watch, the only serious risk it poses, Kirk assures me, is when one dives alone, as spearfishers often do. Last year, blackout claimed twelve spearfishers in Hawai‘i and about that many in California. The 2004 death of Gene Higa, one of Hawai‘i’s most accomplished spearos, was a stark illustration that even experienced watermen are vulnerable. When diving with a buddy, though, there’s not much danger; a few moments after rescue, a blacked-out diver will wake up. They might be disoriented, sheepish and physically exhausted, lips blue or even black from hypoxia, but they’re otherwise undamaged.

The idea that brain damage occurs from extended breath holds—even after a blackout—is a myth. “Brain damage occurs 4 to 6 minutes after you have no pulse, or when you’re anoxic,” says Kirk (anoxia being a total lack of oxygen). “When you hold your breath, you’re only hypoxic; there’s still oxygen in your lungs, your muscle tissue, your hemoglobin. Holding your breath for 4 minutes in the workshop, you’re not even close to brain damage.” He smiles. “Except maybe for the brain damage necessary to be there in the first place.”

Freediving, then, even to triple-digit depths, is, ironically, pretty safe as far as extreme sports go. “I can’t think of many other sports where you don’t end up with bruises or broken bones if you mess up,” says Mandy. “I’ve never broken anything freediving,” she smiles her characteristic sweet smile. “Except records.”

Still, I’m curious. I ask Mandy whether in her freediving career she’s ever had any truly harrowing moments.

“Have you smelled Kirk’s wet suit?” she says. “That’s truly harrowing.”

The first day of the workshop is devoted to the basics: safety, mock rescues and breath work. We learn to hold a “peak inhalation,” to completely fill the pulmonary airspaces, even the trachea. We lock the throat and relax the rib cage so the sensation of pressure doesn’t create an urge to exhale prematurely. We learn an advanced technique called glossopharyngeal inhalation, or “packing”—taking extra sips of breath, as though through a straw, after peak inhalation. (Don’t try that at home; freedivers have broken ribs and perforated tracheas from overpacking).

On the morning of the second day, we’re in the pool at Jack’s, ready to test our pulmonary mettle in static apnea. We’ll start with a 1-minute hold and work our way up. In between holds, we’ll do our breathe-ups, ventilation patterns that lower the heart rate, load the blood with oxygen and blow off carbon dioxide. I tell myself I’ll be happy if I can just beat my personal best, 1:28, but the truth is I won’t be satisfied unless I hit that magic 4:00.

I finish breathing up, take a peak inhalation and go down. Now my only job is to relax. Muscle tension burns oxygen, so I go gelatinous. Just as I’m getting comfortable, Kirk calls 1 minute. Easy. I surface, breathe up and go back down for two. Easy again. Suddenly, 4 minutes doesn’t seem so improbable. I’ve already beaten my personal best, so I relax even more; I’m playing with the house’s money now. After a 2-minute breathe-up, I go down for three, thinking it’s going to be all sweetness and light.

And for 2:20 it is. But at 2:21 my diaphragm decides it’s had enough. It starts kicking, which feels like being punched from the inside. “That contraction is a false sense of fear,” Kirk had told us. “You’re not out of oxygen. When the diaphragm is stretched, it sends the signal, ‘breathe.’ But once you understand what that feeling is, you control it. It doesn’t control you.” Reassuring in an abstract way, but those contractions are extremely concrete, and they don’t ease up. I struggle to 3 minutes, but all my confidence has evaporated. Three minutes is pretty good, I think. Good, but not Tiger Woods good.

The contractions start again 2:30 into my 4-minute attempt. The idea of pushing through them for another 90 seconds is intolerable, so I stop thinking about it. Thoughts of David Blaine renew my determination, but it’s going to take something more powerful than force of will; it’s going to take surrender. “Beyond 3 minutes you hit some real physiological roadblocks,” Kirk said. “About eight different mechanisms are throwing up sensations like you’re out of air. If you’re not ready for it, you panic: ‘Get me the hell out of here,’ your body says, when all you need to do is relax, and the sensation subsides.”

Yes, “get me the hell out of here” pretty well describes it. By 3:15 all eight of those mechanisms are in open mutiny. The carbon dioxide receptor in my brain is worried that the captain has gone stark mad, and the oxygen receptor near my heart radios to my diaphragm for help. My body’s going into oxygen conservation mode by shunting blood away from my extremities to vital systems—the heart and brain. If I persist, my body will eventually resort to more stringent conservation measures, i.e., blackout. By 3:30 I’m fighting, certain I won’t make it. By 3:45 I surrender to the suffering. At 4 minutes, I’m inexplicably relaxed again (what do you know—Kirk was right), even though various new tremors are wracking my body, so I keep going: 4:15, 4:20. When I surface, it takes a moment for the world to untwist itself.

I give an OK sign to Sergio, who’s grinning. “4:30! You rock, Shapiro!”

I have buttered my toast with Tiger Woods, and I have eaten him for breakfast.

Every student has ticked off a personal best; even the shortest hold surpasses 3 minutes. But the valedictorian is Sergio. He comes up wobbly from hypoxia, a loss of motor control that freedivers call a samba (because that makes it sound kind of fun, actually), but he’s made it to 5:45. Two days ago that would have seemed stratospherically remote. Today I wonder if maybe I could do it.

I get it now, the addiction, why people push their limits even to the point of blackout. “You’re never satisfied,” Mandy says. “If you come up clean, you know you could have done more. But how much more?”

Indeed. How much more? It’s liberating; I’ve exceeded what I had assumed was a hard-wired physiological limit—exceeded it by orders of magnitude. “Once you break boundaries in this area of your life,” says Mandy, “you start breaking them in others. You realize that you can do more than you ever dreamed possible. It changes you.”

“Yeah,” I say. “But is it worth it? I mean, does it help you get chicks or something?”

Kirk shoots a glance at Mandy. “I have no complaints,” he says.