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The San Francisco 49ers' two-year rise from the depths of mediocrity is widely attributed to ferocious defense and the dazzling running ability of quarterback Colin Kaepernick.

But as the 49ers head to Atlanta favored to beat the Falcons this weekend and advance to their first Super Bowl in 18 years, here's another possibility: Maybe it's that they stretch a lot.

That's not a proposition you'd want to state too loudly in the 49ers' locker room. The San Francisco stretching program is something team officials refuse to talk about, ostensibly for competitive reasons. But let's face it: The same 300-pound linemen who quickly brag about how much weight they can bench aren't likely to admit that they can do the splits. That's the province of cheerleaders, isn't it?

Privately, 49ers coach Jim Harbaugh has made it clear that stretching isn't for sissies, for good reason. Stretching, research shows, can dramatically reduce the risk of injury, and nothing about the 49ers is more remarkable than their bill of health. Since Harbaugh took over the team two years ago, Niners players have missed 159 games due to injury. (A missed game is one player missing one game.) According to Stats LLC, the three other teams left in the playoffs have had dramatically higher injury rates. Over the past two years, the Falcons have missed 29% more games and the Baltimore Ravens 94% more than the 49ers. The New England Patriots' number is 440, an injury rate 176% higher than the 49ers.

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San Francisco 49ers/Getty Images
Ahmad Brooks gets stretched in the locker room.

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San Francisco 49ersGetty Images
Chris Culliver loosens up on the field.

Several 49ers say the explanation is a stretching regimen. "We do these old school stretches—heavy, heavy squats with chains, a lot of flexibility, a lot of warming up when a lot of people in the NFL skip warming up," said safety Donte Whitner. "That's why we have a good, healthy football team right now."

That the 49ers stretch religiously may seem less surprising than that other teams don't. But, actually, stretching often gets short shrift compared with weight lifting, agility drills and sprints. Mike Bracko, a sports physiologist based in Calgary, said stretching is considered a much lower priority in the NFL than "diets or weight training or jump-training."

What the 49ers do, according to quarterback Scott Tolzien, isn't much more than what is done in pee wee football or grade-school physical-education class. But en route to the NFL, players often lose that discipline, sometimes assuming that their superior ability confers a similarly superior defense against injury.

In the 49ers training facilities, however, it's P.E. class all over again. Before lifting a single weight, a 49er must hit a cardio machine for 10 minutes, a muscle-warming tactic shown to ward off injury. From there, on the field, the team has simple but crucial periods of basic stretching before and after each practice (something overlooked by many teams, players say).

Then, in the locker room, the hard-core stretching begins. One example is a deep squat, wherein a player bearing as many 45-pound plates as possible squats low enough to lightly touch the seat of a chair, then rises and repeats the exercise as many times as possible. While building muscle, that exercise also increases flexibility and range of motion throughout a player's core, increasing agility and speed.

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According to Whitner, a seven-year veteran who previously played for the Buffalo Bills, most teams rarely do much institutional stretching. He said most players simply lift weights to build strength and go through drills that rarely mimic what actually happens on a football field.

"Usually I'm sore; I haven't been sore lately," said rookie running back LaMichael James, attributing that improvement to the team's stretching routines. "Obviously it shows because everyone's still healthy. No one has hamstring problems or muscle problems. Everyone is even keel. A lot of it goes out to us getting inside our muscles."

Men, even when they are highly paid athletes, have a hard time accepting that flexibility is a crucial component of fitness, said Tony Horton, creator of the P90X workout videos. A collection of 12 workout tapes, P90X is wildly popular among people—including professional athletes—who want to get or stay buff. But for many men, the most difficult part of P90X isn't its heavy emphasis on pull-ups and push-ups, but rather its relentless call for stretching and warming up.

"Stretching requires patience, holding the same pose for five breaths, and men aren't patient—they like to keep moving," said Horton, a personal trainer whose clients have included professional athletes. "Women enjoy stretching, generally speaking, and men don't. But in any workout the payoff comes when you do the stuff you don't enjoy and aren't good at."

Linebacker Clark Haggans arrived in San Francisco this year and wasn't surprised to hear the training staff address the four major types of lifting weights. He was surprised, however, that they spent just as much time talking about flexibility, requiring players at different positions to perform different stretches. Initially skeptical, he is now sold. "It's kept our muscles from doing something funky," he said.