The answer comes in unison: "All of it." The wrestlers, now all in, go all-out for the final two minutes.
Christensen tells the story and reaches for his backpack. He pulls out a sweatshirt, a gift from the team, that has Coach Terry across the back. Under it is his trademark question: How much you got left?
Christensen was diagnosed with a degenerative disease of the optic nerve in the fall of 1994. He was legally blind, he said, within about eight weeks.
How much did he have left?
Eight years later, he earned a master's degree in interdisciplinary studies. Four years after that, he earned a master's in history of science. Three years after that, in 2009, he earned a doctorate in history of science from Oregon State.
So he knows perseverance. And the Cougars know he knows it.
"It's so difficult to get a Ph.D. alone, but to do all the reading and all the research without your eyesight, I think, is incredibly hard," said senior captain Cyrus Vakili, who had the sweatshirts made.
"He must have pushed himself incredibly hard."
Christensen, 60, is in his fifth season as a volunteer assistant coach at George School. He cannot be paid, he said, because of a school rule that requires an assistant wrestling coach to be able to drive the team van. ("Nobody is anxious to see me behind the wheel of a George School van," he joked.) Christensen is a paid junior-varsity coach for the football team, which uses buses, not vans.
His eyesight is about 20/800, well beyond the 20/200 that defines legal blindness, and he says it's hard for him to see beyond a few feet. He has a guide dog, an engaging yellow lab named Zane, who accompanies him to practices and matches.
"If you think of the optic nerve as a pipeline that carries information from the retina back to the visual cortex, instead of an intact pipeline, I have more of a gardener's soaker hose. So not much information gets back," Christensen said.
"It's like looking through waxed paper or fog, and there are pin holes in the waxed paper. But the pin holes are not the same density; there's not the same number of them; they're not in the same place. From isolated pixels of information, I'm assembling a complete picture."
Christensen can get close enough to the action in practice to get a complete picture. But during matches, he sometimes relies on verbal cues from the coach sitting beside him, usually head coach Pacho Gutierrez.
Occasionally, maybe twice in a match, Christensen picks up bits of information with his eyes and reaches the wrong conclusion. Gutierrez taps him on the leg to alert him to the mistakes. But the positives far outweigh the errors.
"He has a pretty good idea and sense of what we're doing wrong, and where we can help," Gutierrez said.
Christensen, a Bensalem resident and Oregon native, built a lengthy maritime career - starting in commercial fishing and going into ocean towing - before becoming visually impaired.
Licensed as a U.S. Merchant Marine deck officer, he also taught for five years in the maritime science department of a community college in Oregon.
He met his wife, Betsy Cadwallader, a George School alum, in Oregon, and they moved east when he was researching his dissertation on theoretical physicist John Archibald Wheeler.
These days, Christensen is working on a biography of Wheeler. He also serves occasionally as a guest lecturer, is a board member for Guide Dogs for the Blind in San Rafael, Calif., and is clerk of Yardley Friends Meeting.
And, of course, he's coaching, preaching perseverance to football players and wrestlers.
"The reason I'm doing this," Christensen said, "is I wrote about mentoring. The most effective mentoring I had was from coaches, and I really enjoy being a part of helping other young people turn that corner, help them see that they have more within themselves than they think."
That message is getting through.
"If anything," sophomore 160-pounder Jermaine Doris said, "he uses his visual impairment to help us get better. He has said things like, 'I see the potential in you, and if you don't, you must be more blind than I am.' And things like that are what really inspire us."
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