The National Football League, one of the largest funders of brain research in the US, has subtly worked to influence research efforts and downplay the link between brain disease and the beloved sport, a new report by ESPN's Outside the Lines alleges.

On the surface, the league and its partners appear to altruistically support scientific studies on the effects of hard-hitting sports, such as football, donating more than $100 million to brain research efforts that may not otherwise have been supported. Behind the scenes, however, the organization has tried to funnel the money back to NFL-affiliated scientists and reneged on contributions when researchers came up with discomforting data, the investigation finds.

In light of the funding environment, some brain researchers have compared the NFL’s actions to those of Big Tobacco in the days when the cigarette makers spent millions of dollars to buy off researchers and fund studies that denied links between smoking and serious health effects.

In particular, the investigation raises new questions about a recent study by NFL-funded researchers that the league used to justify ditching impact-tracking sensors in players' helmets. Although the data showed that two tested sensors were 96 percent accurate at detecting impacts and only a few degrees off at detecting the point of impact, the researchers and the league argued that the sensors were significantly flawed and shouldn’t be used in players' helmets.

On the heels of that decision comes a new animal study from independent researchers that suggests that taking successive concussive knocks to the head without any rest in between can lead to permanent damage—something that would be easier to avoid if those knocks were electronically tracked.

"This whole idea that we don't need to use sensors at all, because they don't give us 100 percent accuracy is really the wrong way to go about science," biomedical engineer Thomas Talavage of Purdue University told ESPN. Such data would be "ridiculously valuable,” he went on, “because if nothing else ... regardless of the system, you'll have a good idea of how much exposure in terms of raw numbers. ... How often do [players] get hit? How often do they get hit in practice? And how often do they get hit in games?"

Talavage and a colleague at Purdue told ESPN that they used to receive research funding from the NFL, but, after seeing the effects of league money on other researchers’ work, the pair has since abandoned the funding opportunity. “We think there's a pretty clear demarcation between the research they did before they were funded by the league or tied to the NFL and the research they did after they were tied to the league," Talavage said.

The NFL only recently became a big backer of brain research. Prior to 2009, the league conducted its own studies, which repeatedly found no links between football playing and brain disease. After that internal research was shut down, the league started offering sizable contributions and donations to independent research efforts—most notably the National Institutes of Health. In 2012, the NFL pledged $30 million to the NIH to support brain research following the suicide death of Junior Seau, the Hall of Fame linebacker who played for the San Diego Chargers. But there were many strings attached to the money, according to documents released under a Freedom of Information Act (FOIA) request. The NFL could offer “research concepts” and cancel funding at its discretion, which it did.

In 2014, the league agreed that $16 million of that money would fund a study about chronic traumatic encephalopathy (CTE), a degenerative brain disease that causes dementia, aggression, and depression and is thought to be caused by repeated concussive and subconcussive blows to the head. Specifically, the study would try to detect CTE in living people, as the condition is currently only diagnosed after death.

The NIH announced the funding opportunity and started a typical grant-review process. NFL-affiliated scientists applied for the funding to conduct the study themselves, but after the NIH awarded the money to an independent group—researchers who had openly hypothesized that many professional football players likely have CTE—the NFL-affiliated scientists challenged the decision. When the NIH stood by the grant decision, the NFL backed out of funding the work.

The NIH put up taxpayer money to cover the study. Still, millions of other NFL-donated dollars have gone to fund research conducted by NFL-affiliated scientists, the investigation found.

One such study, published last year in Annals of Biomedical Engineering, tested the accuracy of two helmet sensors, already used in some college teams and widely used in research. The authors found that the sensors were 96 percent accurate at detecting impacts, yet they quibbled with the sensors’ ability to detect where on the helmet an impact occurred. “Overall, our laboratory findings indicate that users should not rely solely on these devices to accurately measure the direction and magnitude of single impacts to a football player’s head at all impact sites,” they concluded.

During the study’s peer-review process at the Annals of Biomedical Engineering, editors there questioned the authors’ standard for assessing the sensors, writing that “it raises questions on the overall objective of this study (i.e., no sensor could ever pass this)," according to e-mails obtained under a FOIA request.

Yet, the study was published and the NFL has cited the work as a reason why it would abandon the use of sensors in players' helmets.The data is sorely missed, particularly as new research suggests that repeated blows to the head—in quick succession with no rest in between—may be key to developing permanent damage.

The new study, published in the American Journal of Pathology, tracked the recovery of mice after minor head impacts (doled out while the mice were anesthetized) that mimic mild concussions in humans. Researchers found that the impact damaged a small percentage of the rodents' brain cell connections and that those connections would naturally recover after three days of rest. But, when the researchers didn’t give the mice those days of rest and instead knocked their heads every day for a month, their brains didn’t recover. Inflammation and lost connections lingered and progressively got worse, the authors report. That damage was still present a year after the last impact.

Though the study was only in a mouse model, researchers think it lends valuable clues to how permanent brain damage might come about in humans—particularly among professional athletes.

Annals of Biomedical Engineering, 2015. DOI: 10.1007/s10439-015-1420-6 (About DOIs).

American Journal of Pathology, 2015. DOI: 10.1016/j.ajpath.2015.11.006