When Rafael Palmeiro was starting out with the Chicago Cubs, he seemed more likely to become the next Wade Boggs than to pass Reggie Jackson on the all-time home run list.

His smooth swing sent singles and doubles skittering through gaps in the defense, but even at cozy Wrigley Field from 1986 to 1988, he only occasionally drove balls over the fence.

Palmeiro added pop when he reached Texas in 1989, but he was still no slugger ... until 1993. That year, he leaped to 37 home runs, from 22 the season before. And he never looked back, hitting 38 or more home runs in nine of the next 10 seasons.

Fans assumed Palmeiro's career progression was normal - a talented young hitter growing into his body. But with the revelation Monday that Palmeiro had tested positive for a performance enhancer, his evolution is suddenly in question.

Could a hitter suddenly transform so completely on his own? Are steroids a likely culprit in such a long and successful career? If he was using them all along, why did he never develop a hulking physique?

Doctors and baseball observers disagree on the answers to these questions. Some say it couldn't be clearer that steroids help players. Others say the impact of such drugs is almost as much a mystery today as it was 10 years ago.

Dr. William Howard, a surgeon specializing in sports medicine at Union Memorial Hospital, said steroids do not turn pedestrian athletes into pros but unquestionably turn pros into stars and superstars.

"Steroids do not help you hit the curveball," he said. "What they do is help build muscle, and what that does is allow you to swing the bat faster. All these guys in the majors can hit the ball. That's how they got there. What they're looking for is that little boost to make the ball go 10 or 15 feet farther."

Steroids aren't magical, agreed Dr. Charles E. Yesalis, a Penn State epidemiologist who studies sports doping, but they add the extra reaction time that can make a good player great.

"When you have something that increases performance in a highly competitive field by half of 1 percent, that's huge," Yesalis said.

The assessments by Howard and Yesalis jibe with the observations of former players who admitted using steroids.

"That's the way I felt, like I could just try to meet the ball and - wham! - it's going to go 1,000 mph," the late Ken Caminiti told Sports Illustrated in 2002. "Man, I felt good. I'd think, damn, this pitcher's in trouble, and I'd crush the ball 450 feet with almost no effort. It's all about getting an edge."

Caminiti grew markedly more muscular and emerged as a power hitter in the middle of a career he had started as a line-drive hitter. Caminiti died of a drug overdose last year.

Despite such empirical examples, many observers are frustrated by the absence of definitive studies on performance enhancers in baseball. Such studies would be hard to perform, because steroids are illegal and Major League Baseball is trying to eradicate, not research, them.

Researchers have been frustrated even in attempts to measure bat speeds to see if they have increased over time.

Will Carroll writes regularly about sports medicine and authored The Juice: The Real Story of Baseball's Drug Problems.

He said he started working on the book because readers often asked him about steroids and he didn't have many concrete answers. More than a year of researching later, he said he still doesn't have many.

"Baseball is a very complex sport," he said. "We know steroids make you bigger, we know they make you stronger, we know they make you faster, but we don't know if they improve your baseball skills."

Carroll's argument is common among those less certain about the use of steroids in baseball. Such drugs have obvious benefits for sprinters or offensive tackles but have a less definite impact on anything involving coordination, their argument goes.