“I feel energized. I feel positive,” O’Brady said from his campsite on Dec. 12, “but there is a reason no one has done it. It’s going to require digging very deep.”

Yet O’Brady’s lead continued to grow. He put in a remarkable 23.3 miles on Sunday and another 21 miles on Monday to reach the top of Titan Dome, the high point of their route. On Tuesday, he faced neither headwind, sastrugi or snow, and there was no incline, either. For once, gravity was in his favor, and O’Brady was free to hammer. He did just that, finishing another lonely, 12-hour trek in Antarctica with 25.5 more miles in the bank.

“I want to get this next leg cracked up, done as quick as possible,” Rudd said on the day he passed the South Pole. Three days later, on Sunday, Dec. 16, with Pink Floyd blaring in his ears, Rudd logged a personal record, 21 miles.

Despite the altitude, and all of their pain and obstacles, O’Brady and Rudd seem to be growing stronger, as counterintuitive as that sounds. Part of that comes down to the conditions. Winds have been light, the surface firmer, and their lightened pulk sleds have been gliding more easily across the ice. But their will to see their expedition through has to be recognized.

He had developed frostnip, a precursor to frostbite, on his nose and cheek, which he was insulating with black tape to keep the areas protected.

This could become an issue, because O’Brady’s calf muscle was already emaciated. He reported that his lower legs “feel more like the size of my arms at this point.” His watch was now sliding around on his wrist, and the cold was starting to get to him, too.

Jenna Besaw, Colin O’Brady’s wife and expedition manager, spent all weekend running formulas to give him the best meal plan possible in terms of daily calories and variety. She gave him instructions to re-ration his food so that each day’s provisions were packed and ready. He would now consume 6,100 calories per day, 900 less than he had been eating since the journey began.

O’Brady said he could easily eat twice his daily rations and according to Jenna Besaw, his wife and expedition manager, he’s been craving dal bhat, a lentil and rice dish served in Himalayan tea houses, that powered him up Everest in 2016. But he didn’t have the option of adding calories to his diet. After setting up camp on Dec. 14, he did a complete inventory of all his remaining food so Besaw could crunch the numbers and determine just how many calories he had left.

Would they have the energy to pull it off? After eclipsing the pole both men reported ravenous hunger.

Having reached the South Pole at 9,301 feet, O'Brady and Rudd weren’t done climbing. Before descending Leverett Glacier toward their finishing point on Ross Ice Shelf they would have to traverse Titan Dome, a plateau which tops out at 10,230 feet.

Devon McDiarmid

Rudd woke to his alarm blaring at 4 a.m., a full three hours before his usual waking time. It was Dec. 13, 41 days into his attempt to become the first person to cross Antarctica alone, unsupported and without harnessing the wind, and the 49-year-old had some ground — or snow, as it were — to make up.

He woke early because he knew O’Brady, the 33-year-old attempting the same feat, was more than a day ahead of him. Rudd was just 15 miles from the South Pole, a pivotal landmark on their journey, but O’Brady had passed the pole the day before.

Ever since the two men had disembarked from their Twin Otter ski plane and stepped onto the Ronne Ice Shelf on Nov. 3, a mile apart, they had been aiming for the flag of the South Pole.

For weeks, both men had struggled through what has been described as the most challenging summer season in Antarctica in over a decade. Snowfall has been El Niño-like. The normally hard, icy surface of the continent has been caked with inches of fresh powder, which makes hauling a 300-pound sled stacked with everything you need to survive in Antarctica for two months, very slow going.