Portis Takes a 'Whale' of a Hit

Redskins running back Clinton Portis, with director of sports medicine Bubba Tyer, has sound reasons for limiting his practice time.
Redskins running back Clinton Portis, with director of sports medicine Bubba Tyer, has sound reasons for limiting his practice time. (By John Mcdonnell -- The Washington Post)
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By Sally Jenkins
Saturday, November 29, 2008

The injuries to Clinton Portis's body take up a wall chart. He's ailing in his knee, hip and ribs, and has scabs on his elbows and shins, which means that only his fanciful head is untouched by physical misery this season. He needed a two-hour deep-tissue massage "just to get mobile" on Monday, he says. After a series of daily rubdowns, hot tubs and ice baths he was able to practice, a little, yesterday. The way it goes for Portis, by the time he finally feels well enough to climb out of his pajamas, it's a Sunday again.

The ice baths are the worst. Every day he plunges his 221 pounds into a metal tub of floating cubes and floes, to reduce the tissue inflammation. He's supposed to stay in it for 10 or 15 minutes, but as it turns his body into a frozen solid, he can't take any more and he jumps up like a push-up popsicle, shivering.

"I can't stand the cold tub," he says. "I have to get out. I'm not big on the ice situation."

Portis's weekly injury status has been a regular topic of conversation for years, so much so that Redskins Coach Jim Zorn engaged in a little light mocking about it this week. Told that Portis had bloodied his elbows and knees in his 143-yard performance against Seattle last Sunday, Zorn screwed up his face in a crying expression and wiped his nose. "Was it squirting out?" he asked.

Portis has always had a light attendance record at weekly practice, but now he hardly shows up at all -- according to Jason Campbell, Portis's teammates see him only on Mondays and Fridays. Ordinarily that's not something a head coach approves of, but Portis is giving such virtuoso performances every Sunday, averaging 4.9 yards on 244 carries, that Zorn can't protest too much.

"He's leading the National Football League in rushing, so what do I know," Zorn says. "It can't even be a goal of mine [that he practice]. It's my desire."

Portis's aversion to practicing is not laziness, he insists. He tells Zorn that he "likes" to practice, news that Zorn greets with arched eyebrows. Rather, it's based on an instinct that the rehab cycle of rest, heat, ice, compression and elevation is a better way to enliven his legs than repetitions on the practice field.

"If you take common folk and hit them across the arm with a bat, they're going to take the proper time to rest," Portis says. "In football you never get a proper healing. You get maybe seven days, and most teams don't allow you that, they need to see you back at practice on Thursday or Friday. You get four days to recover being hit by a bat. And then you get hit by another bat. Common folk get hit by a bat, they might not go to work for two weeks."

Portis's instinctive calculation that he needs to seek "a proper healing," even at the cost of sarcasm from his coach, is the correct one, according to Robert Gotlin, director of Sports Rehabilitation at Beth Israel Medical Center in New York. Portis's injuries are classified as an assortment of strains and sprains, but those words are commonplaces that don't adequately express the collisions that inflict them, or the hot irons of pain that result. Strains and sprains are actual tears of muscle and ligament. Most NFL players who suffer them don't get better during the regular season even with weekly rehab; they only hope they don't get worse. Portis can expect to be healed around April.

"The reality is, they probably never fully recover until the offseason," Gotlin says. "If he started with 100 points, he's down to 80, and it's very difficult to get to 100 again during the season."

Every player in the NFL, at every position, suffers physical trials. But it's fair to say that an NFL rusher with as many carries as Portis absorbs an especially intense battering. Zorn calls Portis one of the most physical players on the field, even when he doesn't carry the ball, a contact seeker who throws blocks even though he's well away from the play.

"If he's here and the pass is over there, your head better be on a swivel," Zorn says. "Somebody is gonna get knocked down. He tries to play the game violently."

Portis is a perfect example of the violence of applied physics in action on a football field. In a fascinating small book called "The Physics of Football," Timothy Gay conducts a series of basic equations to help us quantify how Newtonian laws work on the body of a running back. Example: Newton's Second Law says that force is the product of an object's mass and acceleration. Let's say Portis sprints through a hole opened up by his offensive line, at a speed of 30 feet per second. Now Giants linebacker Antonio Pierce enters the picture. Pierce hits him; Portis's speed immediately after the hit is zero. It takes two-tenths of a second to complete the tackle, from the initial contact of the pads to the moment when Portis's forward motion is completely stopped.

Dividing Portis's speed change by the time interval over which it occurred tells us what Portis's rate of deceleration was -- about 150 feet per second squared. Now multiply it by his mass, to find out how much force acted on him. Gay's equation works out to negative 1,150 pounds of force. In other words, about three-fifths of a ton slammed him in the backward direction. As Gay points out, "That's the weight of a small adult killer whale."

Says Portis, "That makes sense to me."

Now take gravity, and changes of speed and direction into account. On another play from scrimmage, Portis plants his right foot hard and shears off at right angles to his initial velocity. Using Newton's Second law, Gay calculates the force Portis has to exert on the ground to produce that acceleration: It works out to about 880 pounds -- about 4 g's.

Some of these conclusions are intuitive, but they can't be repeated enough. Gotlin, the physician, puts it in even more simply quantifiable terms. On a jump cut, Portis may force "as much as six or seven times his body weight through his right knee."

Last season, Portis carried the ball 325 times. Doing the most basic math, at this rate he can expect to be hit by another 80 or 90 small adult killer whales before his season is over. It's safe to say his knee, hip and ribs could use a few days of rest between efforts.

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