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WASHINGTON (AP) — Back in August 2011, the NFL and the players' union signed off on a new labor deal that set the stage for the league to test for human growth hormone, perhaps as soon as a month later.

Nearly two full seasons have gone by and nothing's happened. The NFL Players Association won't concede the validity of a test that's used by Olympic sports and Major League Baseball, and the sides haven't been able to agree on a scientist to help resolve that impasse.

The congressional oversight and government reform committee is holding a hearing on Wednesday to take a look at the science behind tests for HGH. It's a substance that is hard to detect and believed to be used by athletes for a variety of benefits, whether real or only perceived — such as increasing speed or improving vision.

"The players are claiming that the testing is questionable. What's bothering me about all of this is that the players made an agreement in 2011 ... that they would begin the human growth hormone testing, and it seems to me that they have thrown roadblocks and found excuses not to do it. And that concerns me. An agreement is an agreement," said congressman Elijah Cummings, who noted that he expects there will be additional hearings.

"We also want to make sure that the players are treated fairly," Cummings said in a telephone interview. "We want to hear the science, so we can make some valid judgments as to the players' allegations that this may not be valid."

A memo sent by committee staff members last week to lawmakers says: "Every week of football played without a test for HGH endangers the game and sends a message to young athletes that HGH is tolerated at the game's highest level."

The memo closes by saying: "This hearing will examine the science behind current HGH testing and highlight the fact that this testing is available to use in the NFL." In a statement issued on Tuesday previewing the hearing, committee chairman Darrell Issa sent something of a warning to the NFL and players.

"There has been a frustrating lack of progress on testing. The possibility that federal legislation could eventually be adopted to address this problem may be unlikely at this point, but the league and its players would be unwise to ignore it," Issa said.

The committee did not ask anyone from the league or union to testify on Wednesday. Scheduled witnesses include Pro Football Hall of Fame member Dick Butkus, U.S. Anti-Doping Agency chief science officer Larry Bowers, and National Institutes of Health deputy director Lawrence Tabak.

In written testimony submitted to the committee, Bowers says "there is a broad consensus among scientific experts who regularly work in the growth hormone field" that the test is reliable and valid, and that "the chances of an athlete who has not used synthetic growth hormone testing positive are comparable to the chance of that same athlete being struck by lightning during his or her lifetime."

Bowers writes that World Anti-Doping Agency records show that as of late August, 12 positive results showed up from 12,764 HGH tests around the world. "I would like to point out that the only people who are still questioning the methodology and validity of the ... test are lawyers, not scientists," his testimony reads.