Carroll cited an Auburn University study that found forearm strength did not equate to hitting power. But, he added, such studies might lose relevance when examining major league players, who are by definition exceptional athletes and are separated by the thinnest advantages in reflexes or confidence.

Carroll said that users such as Caminiti and Jason Giambi (whose revelation was made in grand jury testimony leaked to the San Francisco Chronicle) probably benefited from taking drugs but said he has no idea how much.

Until Monday, such questions had centered on muscular sluggers such as Barry Bonds, Mark McGwire and Sammy Sosa.

Many scratched their heads when Jose Canseco said he had injected Palmeiro with steroids when the two were teammates in the early 1990s. Palmeiro jabbed his finger in the air as he denied Canseco's charges at congressional hearings in March. Fans and lawmakers alike deemed his indignity credible.

Palmeiro had never seemed a classic steroid case. He's not unusually bulky for a ballplayer; he's known more for smoothness than hitting tape-measure home runs; he has been preternaturally consistent; and he has never experienced the nagging pulls and strains associated with hulking sluggers.

But the effects of performance enhancers can be subtle, experts said.

"Taken in small amounts, they help you heal," said Howard, noting that Palmeiro has been uncommonly durable throughout his career. "It's only when you take them in larger amounts and hit the weights that you get too strong for your joints and start to get injured more."

The fact that Palmeiro was never a hulk also doesn't mean much, researchers said. He could have injected the drugs for years without growing if he never lifted weights vigorously.

"Was he taking something? Probably," Carroll said. "Was he taking it over a long time? Probably. But was he getting any effect? We don't know. The idea that you can pick out steroid users by appearance is laughable."

Palmeiro's power spiked shortly after Canseco became a teammate and, according to Canseco's book, introduced Palmeiro to steroids.

This season, Palmeiro started slowly, but his average began to climb in May, just after he reportedly tested positive. Researchers are reluctant to link such short-term performance swings to drug use, saying random chance is the more likely explanation.

Palmeiro's career progression is unusual but not unprecedented. Most big-time sluggers start hitting home runs early, but many players add power as they mature.

Stan Musial was a slashing line-drive hitter who never hit more than 19 homers in a season before he was 27 but ended up with 475. Carl Yastrzemski followed a similar track, never hitting more than 20 homers before he turned 27 but drilling 44 that year and finishing with 452.

Palmeiro had his first big power season at 28 and has 569 homers, eighth all-time.