"It seems [the union's objection] is not based on science," WADA chief David Howman said. "You're better [off] to expose yourself to a test than decline it, because the impression you leave is that you have something to hide."
The new NFL labor contract allowed HGH testing as early as this season but only if the players' union approved the tests.
Last week Major League Baseball players in their new collective-bargaining agreement agreed to HGH testing in 2012. And NFL owners want their players to commit to a similar HGH-testing policy.
But the football players' union has balked at consenting to HGH testing, saying it needs more information about the procedures.
"We'd be willing to proceed and agree to any test that was verified for its scientific reliability by the broader scientific community, not just WADA's," NFLPA spokesman George Atallah wrote to the league last month. "We don't trust their scientific review process."
The NFL players' union wants to study the population data used by WADA to learn what qualifies as a positive drug test, and to know if the testing protocol is based on Kenyan marathon runners or women skiers and how that correlates to testing a 300-pound offensive lineman.
Scientists who spoke at Thursday's Partnership for Clean Competition meeting — a conglomeration of anti-doping efforts in MLB, the NFL, NBA, NHL and the U.S. Olympic Committee — said the population data is irrelevant to accurate HGH testing.
Dr. Gerhard Baumann of Northwestern University discussed how current HGH testing allows detection of the drug only within 24 hours of use, but that a more advanced test can detect drug use "up to a week or more." That test is nearing WADA implementation, officials said.
"I believe it to be imperative to all parties involved to implement [drug] testing to ensure the utmost of integrity," NFL spokesman Adolpho Birch said at the conference, conducted at NFL offices.
Among the speakers Thursday was Jeff Novitzky, a Food and Drug Administration special agent, who has investigated seven-time Tour de France champion Lance Armstrong.
"These drugs are being used as guinea-pig experiments on the athletes … it trickles [down] to our society and the youth of our society," Novitzky said. "Most of these athletes [who use] are good people. Good people who made bad decisions."
Howman said his work is now focused on improving drug testing before the 2012 Olympics in London.
"We're sending the message: You don't want your country to be embarrassed by a positive test at the Games," Howman said. "The athletes better be tested before they leave your shores."