The NFL will not outfit players with helmet sensors next season, indefinitely delaying the implementation of technology that has been championed by one of the league's own medical advisers as a way to reduce concussions.
The decision was confirmed Thursday to "Outside the Lines" by a league spokesman, who said the NFL "will continue to review and analyze the research." The NFL Players Association said it supported the decision.
At least 20 colleges -- including Virginia Tech, UCLA and North Carolina -- employ helmet sensors to alert coaches and medical personnel to potentially damaging head trauma. The sensors show where a collision occurred and estimate the amount of force that was generated. A number of institutions use the technology to conduct concussion research, much of it funded by the government.
The sensors could enable the NFL to answer a number of fundamental questions -- how many head hits players absorb, the force of those collisions and where they most frequently occur. In June 2014, Dr. Kevin Guskiewicz, an NFL adviser and concussion researcher, told USA Today Sports that two companies were "fine-tuning" their devices and that all 32 NFL teams could be using the sensors during the 2015 season.
But the technology has been plagued by controversy, resistance from the players and questions the league has repeatedly raised about its reliability.
Dr. Robert Cantu, a Boston neurosurgeon and concussion expert who serves as an adviser to the NFL's Head, Neck and Spine Committee, said Thursday that he remains unconvinced sensors can measure head impact with enough accuracy to provide useful data.
"For me personally, until the validity issues are further sorted out, it can be argued, I think, that sensor studies are fairly preliminary," Cantu said. "I would want to know how accurate these devices are."
But Stefan Duma, who leads Virginia Tech's Department of Biomedical Engineering and Mechanics, said the reliability of the sensors has been established for years. Although subject to error, he said, the technology enables on-field personnel to respond quickly when a collision occurs and determine whether it caused an injury.
The system, in use at Virginia Tech, alerts trainers when it detects any hit measuring at least 98 g forces. Duma also uses the sensors as the basis for Virginia Tech's football helmet rating system, which is widely used by consumers. He receives funding from the National Institutes of Health, the Centers for Disease Control and the Department of Defense, among other agencies.
Duma described the NFL's reservations as "analysis paralysis."
"Our view is that while there are limitations, it still gives you very useful data," he said.
The sensors' champions have included Guskiewicz, a former Pittsburgh Steelers assistant trainer who is now senior associate dean for the natural sciences at North Carolina. Guskiewicz, who co-chairs the NFL's Subcommittee of Safety Equipment and Playing Rules, used UNC sensor data to persuade the NFL to move kickoffs from the 30- to the 35-yard-line, a change the league credits for a decline in concussions.
It was unclear what role Guskiewicz played in the NFL's decision to delay implementation. Duma, who in the past has worked with Guskiewicz, said, "Kevin appears to have been marginalized or that this was taken away from him." He added that he had no direct knowledge about Guskiewicz's status.
In an email, the NFL spokesman referred questions about the helmet sensor initiative to Guskiewicz, writing that he "led the project as a member of the league's Head, Neck and Spine Committee." Guskiewicz was unavailable for an interview.
According to Cantu, the NFL recently commissioned a study of two of the possible sensor systems: the Helmet Impact Telemetry System (HITS), which uses battery-powered sensors implanted in the helmet's padding, and X2's mouth guard sensor. The HITS system, which was developed by Simbex, a New Hampshire biomechanics firm, is marketed to consumers by Riddell and is used by 20 NCAA football programs.
Although the results have not been published, Cantu said the study raised further questions about the accuracy of the sensors, particularly when measuring impacts to the facemask and the back of the head. The study was performed by Gunter Siegmund, a biomechanics expert in British Columbia.
Some proponents of sensors believe that, for years, the NFL has sown doubts about reliability to justify widespread resistance. The NFL Players Association also is opposed to the use of helmet sensors in their current form. In 2012, former Steeler Hines Ward told "Outside the Lines" that the sensors would open up a "Pandora's box" by providing data that could be used to remove players from games or even in contract negotiations.
On Thursday, the NFLPA indicated it has continuing concerns about the confidentiality and reliability of the data. The union asserted that a recent "field trial" revealed that the sensors are "not nearly as useful as had been hoped and in many cases could not even determine the direction of the forces," causing the study to be suspended.
Rick Greenwald, Simbex's president and co-founder, said he was unaware that the NFL had made a decision to delay the implementation of helmet sensors. But he said the system's usefulness ultimately depends on the type of information the league is seeking.
"We think it's a tool that's well-documented for providing information about how often, how hard and where you get hit," Greenwald said. "I'm not sure that sensors would meet NFL validation requirements even if they were screwed to the players' heads."