In his 15 years of professional football, Oakland Raiders center Jim Otto never missed a game. Torn knee ligaments didn't stop him. Neither did a cracked kneecap.
Otto, considered among the best to play his position, needed nine off-season knee operations to stay in the game as long as he did. He retired in 1975 as a sure Hall of Famer - he was inducted five years later - but the damage to his body was already done.
Few professions cause as much wear and tear on the body as football, a sport so injurious that the average career lasts not quite four years. The physical toll can last a lifetime.
For Otto, constant poundings on the line of scrimmage left the cartilage in his knees, shoulders and spine virtually ruined, setting the stage for degenerative arthritis that will plague him for the rest of his life.
"Since I retired, I've had 21 surgeries on my knees," he says. "Both knees are artificial. Both shoulders are artificial. I've had five fusions in my lower back where there's no disc anymore. I had three infections that got into my knees and almost killed me."
Otto paid a heavier price than the average professional football player. But few who have played the game that reaches its annual climax on Super Bowl Sunday have spent their retirement without painful reminders of the punishment they took on the field.
For Johnny Unitas, the great Colts quarterback, it's nerve damage that has left his right arm unable to grasp, much less throw, a football. For Sam Huff, a former New York Giants and Washington Redskins linebacker, it's a searing pain that radiates from his jaw through his skull.
For Harry Carson, a former Giants linebacker, it's headaches and memory loss caused by repeated concussions. For Bo Jackson, a Raiders tailback who was considered one of the greatest athletes of his era, it's bilateral hip replacements.
Rare is the retired player who can say - as former Raider Ben Davidson does - that he has not suffered physical repercussions of his playing days.
"I have no arthritis, no pain," says Davidson, a 6-foot-8 defensive end who starred for Oakland in the 1960s and later appeared in beer commercials and light feature films. "I had a personal creed: `Do unto others before they do it to you.' On the Raiders, opposing players knew that if they did something to you, somebody would do it to them. It probably made for safer conditions."
Maybe, but probably not. Otto played on the same line as Davidson but has suffered so much that retired players sigh at the mere mention of his name.
For his part, Otto guesses that his "reckless" style of play - "going all out, trying to make every block with reckless abandon"- contributed to his injuries.
The answer may be more complicated.
Dr. Scott Graham, a Cleveland orthopedist who has treated former members of the Browns, says arthritis, though common among retired football players, isn't inevitable. Genetics also plays a role.
"Not everybody who has those injuries goes on to have arthritis down the road," he says. "It's multifactorial. If you have bad genes and an injury, then that's the worst-case scenario."
It doesn't help that players have bulked up to the point where linemen typically weigh well in excess of 300 pounds. Their bulk means more wear and tear on cartilage and ligaments; it also means more damage to the unfortunates on the other side of the line.
There is no easy fix for torn cartilage. Surgeons can snip away the damaged tissue, reducing the friction that occurs with each flex of the knee. But over time, successive knee operations mean less cartilage buffering the knee - possibly setting up the chronic inflammation that is osteoarthritis.
Dr. James St. Ville, a Phoenix orthopedist who has treated 250 retired football players, says shoulder injuries tend to strike quarterbacks and wide receivers, while knee injuries are more common among running backs, linemen and safeties.
Players who balloon to 330 pounds but stop exercising when they retire might be at higher risk for heart attacks, diabetes and stroke, doctors say.
"The life span of a lineman is probably not as high as the average person and certainly not as high as people like wide receivers," says Dr. Bill Howard, a sports-medicine physician at Baltimore's Union Memorial Hospital.
Repeated concussions - an occupational hazard of quarterbacks - can also set the stage for memory and concentration problems later in life.
Some doctors believe that each successive head injury raises the risk of permanent damage, a concern that drove San Francisco 49ers quarterback Steve Young to retire and has sparked calls for the Dallas Cowboys' Troy Aikman to do the same.
Each injury has its own story.
Huff, who played 13 years, considers himself lucky. Despite the relentless hitting that was his trademark, he avoided major damage to his joints. But an encounter with Jim Brown, the great running back, accounts for the facial pain that afflicts him to this day.