Players endure tough practices and a brutal season in hopes of reaching the Super Bowl, arguably America's biggest annual sporting event, drawing millions of viewers.
However, the physical beating that a player's body experiences during any NFL football game may bring upon what is ahead when the games are over, the lights are off and it's time to hang up the cleats.
In 2003, the average NFL player was listed at 6-feet-1.5 inches, 245.2 pounds, often with the ability to run 40 yards between 4 and 5 seconds. That kind of mass in concert with that kind of acceleration is the standard scientific definition of force. That force is exerted for a full hour of playing time in the way of hitting, pushing and tackling.
An NFL career often ends with aches, pains and ailments that can stay with ex-players for the rest of their lives.
In 1988, during a game against the Denver Broncos, Detroit Lions fullback Scott Williams took a hit that knocked his shoulder out of place. A trainer aligned it and sent him back to finish the game. The following week against Dallas, he dove for a fumbled snap and it came out again, resulting in major surgery and a shortened career.
"That was the major injury that I had in the NFL," Williams said. "I probably have 90 percent of the range of motion."
Williams is now a sales executive for Turner Broadcasting System in Atlanta, and says he works out four to five times a week to keep that 90 percent range and to stay in shape.
Three years after that game, teammate Mike Utley on Nov. 17, 1991, suffered a far more memorable injury during a game against the Los Angeles Rams. Williams remembers the day and the play very well.
"Yes sir, horrible injury," he said. "It looked like he slid off of a block and fell to the turf, landing on the crown of his helmet. It was a freak accident that left him paralyzed."
Utley injured his sixth and seventh vertebrae, leaving him wheelchair-bound and ending his career.
Utley's injury may have been the most frightening since Lawrence Taylor broke Joe Theismann's leg and ended his career in 1985, or Oakland Raider Jack Tatum broke Darryl Stingley's neck in an Aug. 12, 1978, pre-season game. Stingley has been a quadriplegic since that day.
Minnesota Vikings player Korey Stringer collapsed during practice from heat exhaustion in the summer of 2001 and died 15 hours later, never regaining consciousness and becoming the first NFL player to die from heat stroke in league history. The 27-year old, 335-pound lineman's body had reached a heat index temperature of 108 degrees on the practice field.
The most severe injuries get the attention of the league and fans, but the concussion is the most common and, perhaps, the most dangerous. A concussion occurs when the brain is shaken or jarred violently within the skull, resulting in a disturbance of cerebral function.
"When you are banging heads, no matter what you do, we are going to have injuries," said Dr. Robert Gotlin, director of orthopedic and sports rehab at Beth Israel Medical Center in New York City. "Over the long term, there is a tremendous pounding on the body just from the head down."
In fact, a 2001 study by the Center for the Study of Retired Athletes based at the University of North Carolina reported that the average number of concussions sustained by football retirees during their playing years was 2.04. A more current study by the center is due out soon.
The study also said retired NFL players who suffered three or more concussions during their playing days are three times more likely to end up with some kind of mild cognitive impairment.
Injuries in professional football are so common that a number of Web sites and services list and explain the usual ailments associated with the game, including http://orthopedics.about.com/cs/sportsmedicine/a/football.htm.
In fact, the NFL requires that all its teams issue a weekly injury report, which is then posted on the league website at http://www.nfl.com/injuries. What the teams and the leagues don't report is the long-term damage to the athletes.