The new test is the latest weapon in WADA's arsenal following the development of tests for the endurance-boosting drug erythropoietin (EPO) and so-called designer steroids such as tetrahydrogestrinone (THG), which have been chemically engineered to deceive the testers.

CNN: Anti-drugs chief confirms HGH test

With that in mind, the NFLPA has requested further information from WADA to better comprehend the underlying science behind the test.

FORBES: HGH Testing In The NFL: League Says Go, But Union's Got Cold Feet

They have both spent time at WADA headquarters in Montreal listening to WADA scientists explain the nuances and finer points of their isoform test.

FORBES: HGH Testing In The NFL: League Says Go, But Union's Got Cold Feet