Virtually every victim of steroids testing has an excuse, which often is met with skepticism, if not outright disbelief.

However, experts in the field say that there is plausibility to Mike Morse's claim that he tested positive in May for steroids use which occurred at least 16 months earlier.

"That is most certainly possible," said Dr. David Black, president and director of the Nashville-based Aegis Science Corp., the largest private doping laboratory in the United States.

Dr. Charles Yesalis, a Penn State professor, said that Morse's explanation is "clearly consistent" with the anabolic steroid nandrolone (commonly known as Deca Durabolin), which reportedly is the substance for which Morse tested positive.

"From what I know, that appears to be a reasonable explanation," said Yesalis, regarded as an expert on performance-enhancing substances.

According to Internet reports of his testimony before an arbitration board on July 19, Morse used Deca Durabolin in November and December of 2003 to help mitigate the effects of a thigh injury. He reportedly switched to Winstrol in January 2004, then said he stopped taking steroids altogether.

Morse has now tested positive three times since then (the previous two times in the minor leagues), and said that each test has shown a decreasing level of steroids in his system.

According to Black, who helped Pete Rozelle set up the NFL's steroids-testing program in the 1980s, no definitive studies have been done on how long oil-based steroids like nandrolone stay in the system.

"There's anecdotal reports of 16 months, but we certainly have every reason to believe it could be longer than 16 months," Black said. "Once injected, it resides in the body for a long period of time."

"These things get in your fat cells and they just hang around forever, seemingly," Yesalis added.

"You get findings that don't indicate current use or use with intent to cheat," he said.

Morse's statement yesterday quoted the three-person arbitration panel as saying it was "undisputed" that the steroids level in his test had "no performance-enhancing effect." The panel, however, ruled 2-1 against his appeal.

Said Black: "When low concentrations are found, it is not indicative of intent to cheat or performance enhancement."

Yesalis, a vocal critic of MLB's drug-testing policy, said that the Morse case "plays right in [commissioner Bud] Selig's hand of trying to convince people there's a few dirty little apples in his barrel, instead of a big, huge chunk of the barrel being rotten."

Asked why more players didn't test positive for the residual effects of steroids taken months or years ago, Yesalis said that Morse appears to have been victimized by his choice of steroids.

"There's other steroids I could give you and have you take that you could be tested for every day, and you're not going to be caught," he said. "Like the creams and gels that used judiciously will keep you under the radar screen."

Larry Stone: 206-464-3146 or lstone@seattletimes.com