After 14 weeks, the drills advanced. Sugarman rolled a soccer ball as Peterson shuffled from side to side in a sand pit, trying to catch it like a goalie and throw it back in the same motion. He ran tight circles around hula hoops on the turf. He sprinted forward as Sugarman held him back with a bungee cord. Sometimes, for fun, they chased each other around the training room on stools with wheels so Peterson could strengthen his hamstring muscles. Or they'd stand on small red discs and toss a ball back and forth.
"He was terrible at it. He just hates to lose at anything," Sugarman said. "So it's great when I can beat him at something."
Peterson started training camp in Mankato, Minn., on the physically unable to perform list. His protest unsuccessful, he realized the importance of taking the process slowly. Those precious last few degrees of flexion in the knee took several months to return. The cutting, stopping and restarting he has to do for his job required nothing less than the full explosive ability of the joint. The muscles around the knee that atrophied after the surgery needed to be recalibrated, with quadriceps, hamstrings and calves in the proper strength proportion to one another.
Peterson began to be integrated into practice, though, with fans and coaches holding their breaths,
"He just dominated the rehab. It was ridiculous," Sugarman said.
Peterson was in the backfield on Sept. 9 as he planned all along, and he ran like he never left, carrying the ball 17 times for 84 yards and two touchdowns in an overtime victory over Jacksonville. He got the game ball afterward, which he gratefully passed on to Sugarman.
The ligament was as strong as ever, as good as new, but that didn't mean the Vikings weren't still nervous, wondering how Peterson would perform.
"I don't really worry anymore. But the first part of the season I was worried sick," Sugarman said.
The rest of the season:
Peterson felt right after the Sept. 23 win over San Francisco, when he woke up the morning after feeling the usual post-game soreness. He truly began to take off on Oct. 21, when he hit the 150-yard mark in beating Arizona. He's passed the 170-yard mark in four of the last six games, twice surpassing 200 yards.
"He was never going to let this injury be an excuse for him not to be at the level he was at, and I think all the people saying he couldn't do it gave him more drive," defensive end Jared Allen said. "That's the competitor in him, and that's why we love him here."
Peterson jumped in the cold tub to recover after Sunday's game at St. Louis. He's still been doing stretching and strengthening exercises on his left leg. Other than that, there's nary a sign of his injury left.
Sugarman has received all kinds of correspondence from coaches and competitors in all levels of athletics, wondering what their secret was. But Peterson hasn't really rewritten the ACL rehab manual. He's just added another remarkable chapter to his exceptional career.
"His ability to heal is probably different than mine or yours. His work ethic. His determination. His faith. He just has all these factors that, when put together, allowed him to accomplish what he has almost a year out from this terrible injury," Sugarman said.
"I don't think it's quite fair for everyone who tears their ACL moving forward to compare themselves to Adrian Peterson. They're setting themselves up for, in most cases, an unrealistic expectation."
Peterson, who is 27, has stated his desire to break Emmitt Smith's record for career rushing. He'd have to play a long time to do that. But after his performance this year, that mark is just as achievable for him as the rest.
"It just depends on how long God blesses me to play," he said. "I might go far and play `til I'm 40. I don't know."