Baseball pitchers, by and large, now have longer careers, thanks in part to conditioning and science. Doctors can save careers of pitchers with torn tendons in the elbow or shoulder--Tommy John's was the first--by grafting tendon from another part of the body and repairing the injured area.
There also use of biomechanics, a computer analysis of motions such as pitching and running developed by physicist Gideon Ariel.
"I remember when that started, many of the older coaches were against things like that," Daly said. "Older coaches in track and field used to think no weight training would work. They thought that filming their athletes running didn't work and that you couldn't teach speed. If there is something wrong with a pitcher's mechanics, they can now stop it and prevent shoulder and elbow problems."
Said Costill: "If you look at activities where orthopedics is involved (football, basketball, etc.) the span of those careers are not as long as non-impact sports. But even swimming and cycling is limited because we've found they lose strength."
Losing confidence in ability is another problem for older athletes.
"Being old is not really chronological, it's mental," said Thomas Tutko, a San Jose State sports psychologist who has worked with professional and Olympic athletes. "I've met athletes who have felt over-the-hill at 23. That's because they have been at it since 7."
Experts say there are no proven physiological reasons why swimmers, particularly women, should be washed up in their early 20s, or why women gymnasts rarely compete past their teens. It is a combination of burnout and a culture in which girls previously have not been encouraged to continue competing.
Costill said swimmers, who also start young, quit well before their bodies tell them it's time.
"Men and women swimmers may quit at 20, but, physically, that's 5 or 10 years short of their peak," he said. "When the '80 Olympics were canceled (at least for United States competitors), a lot of swimmers--such as Rowdy Gaines--hung around until the '84 Games and they were still physically able to do it. They had the motivation."
Ravizza, who has worked with teen-age gymnasts and figure skaters, said that early burnout often is inevitable.
"Girl figure skaters work 50 weeks a year, 6 hours a day for 6 days a week since age 9, and burnout appears often, especially when they hit a streak when there is no reward (major competition)," Ravizza said. "The sport loses its meaning to them. It starts manifesting itself in their performance . . . When the stresses have more impact on them than the enjoyment, that's when you see burnout."
Said Tutko: "I usually find burnout in sports where a lot of practice is necessary. All of a sudden, it's not worth it."
Tutko says that most of the cases he sees involves athletes trying to hold on past their primes.
"They worry about what they are going to do after sports," he said. "A lot of denial goes on. Usually, they think it's just temporary, that they'll get it back."
Perhaps one reason professional athletes want longer careers is that the money is so good that they take a severe pay cut once they retire. It wasn't like that two or three decades ago.
"Of course, they look at the money as a motivation to keep playing," Daly said. "But there also are guys who just do it out of pride, who have built up their body to do whatever they want it to do. They don't think it can betray them."
Eventually, of course, all athletes must retire. When that happens, it is no longer essential to an athlete's livelihood that he stay in shape and their once hard bodies become as flabby as the rest of us.
In fact, sometimes former star athletes let themselves go to such an extent that the expression "larger than life" takes on more than one meaning.