Researchers tracked rookies during the 2006 through 2011 seasons and found strength measurements taken at the annual Scouting Combine - held before teams select their new players - were no different among those who did and didn't go on to have an injury.
"There's been this belief for years and years that certain differences between muscles were important" for injury risk, said Dr. John Zvijac, who led the study at the UHZ Sports Medicine Institute in Coral Gables, Florida.
But the new findings, he said, suggest players and coaches shouldn't give too much weight to so-called Cybex data.
"These numbers really aren't the dogma that we thought," Zvijac told Reuters Health.
"The beliefs that we've had up until this study - many of them have changed because of the data we have come up with."
Using trainers' records, Zvijac and his colleagues found 164 players who had a hamstring injury during their rookie NFL season and more than 1,100 uninjured players to serve as comparisons.
As expected, injuries were more common for players in positions that required lots of running, including running backs, defensive backs and receivers.
However, none of the data collected during the Combine, including the relative strength of players' quadriceps and hamstrings, predicted an injury in the following season, the researchers reported in the American Journal of Sports Medicine.
The Combine is typically held in February, followed by the NFL Draft in April or May and the start of preseason training in July.
Although the most hamstring injuries happened during the preseason, the researchers said it's possible that training or deconditioning after the Combine made the Cybex data collected there no longer relevant.
The Combine strength testing is done using equipment made by CSMI Medical Solutions. The company was not able to provide a comment by press time.
Zvijac said Cybex data are used by all sorts of athletes, including Australian football players and soccer players. But they don't seem to predict injury-related outcomes.
There are probably many factors that do influence who suffers a hamstring injury, the researchers said, such as flexibility, fatigue and posture.
Bing Yu, from the physical therapy division at the University of North Carolina at Chapel Hill, said over-stretching of the hamstring muscle is a direct cause of strains.
"Increasing flexibility is one of the ways to prevent muscle strain injury such as hamstring injury," Yu, who wasn't involved in the new research, told Reuters Health in an email.
"Also, using appropriate techniques and having appropriate movement patterns are also very important for preventing injury."
SOURCE: http://bit.ly/13IwX4l American Journal of Sports Medicine, online May 28, 2013.
[This refile corrects story posted Jun 6, 2013 to remove extra character from headline. Article text is unchanged.]