‘The Gains That Could Be Made Would Be Enormous’

In a sport where a fraction of an inch can be the difference between safe and out, or ball and strike, and where big money is paid to those who prosper, an opportunity to gain an advantage without detection could be too hard to forgo.

“Sports has learned the hard way,” Ross Tucker, a sports scientist in South Africa with a Ph.D. in exercise physiology, said in a recent phone interview. “Antidoping without out-of-competition testing is basically meaningless.”

He added later, “The analogy always was that antidoping was trying to shine the light into a dark tunnel, and just trying to catch that athlete at the moment that they walk through or drive through that dark tunnel. Now you’ve got basically a blackout.”

Tucker explained that some of the steroid hormones that athletes have used before, particularly when injected in high doses, take a long time to clear from the body and can be detected for weeks after. But if athletes are using oils or creams with low dosages, he said, their chances of evading detection could improve.

“If they do that, and then they get notice saying, ‘Right guys, you’re back in training in a week,’ they would be clean within a week of that notice,” Tucker said. “And if they’ve trained adequately over the period in which they’re doping, they will have improved their strength and their power and their muscle mass significantly. And as long as you keep training after that, you just defend it.”

Tucker said if athletes properly trained while using steroid hormones, the gains could last at least six months to maybe a year, if not longer. Over the course of the grueling 162-game M.L.B. regular season — not including weeks of spring training and a month of the playoffs — players can lose weight and muscle mass. But a player starting from a higher base level thanks to doping, Tucker said, would have an advantage over one who did not.

“You might start seeing some 50-home run seasons again,” said Victor Conte Jr., the central figure in the BALCO steroids scandal that linked the use of P.E.D.s to some of the country’s top professional baseball, football and track and field athletes. In 2005, he pleaded guilty to distributing steroids and money laundering.