The Free Press, Mankato

Today the Minnesota Vikings begin full-team workouts in their 52nd, and final, training camp in Mankato. They, and other teams on all levels preparing for the 2017 season, do so under a gathering medical cloud.

Earlier this week medical researchers announced that 110 of 111 brains donated by families of former NFL players showed signs of the neurodegenerative disease chronic traumatic encephalopathy, or CTE.

The findings go beyond the professional level. A total of 202 brains of deceased football players were examined, and CTE was found in 177 (87 percent). CTE can only be diagnosed after death.

These findings don’t mean that everybody who plays football sustains lasting brain damage as a result; the 202 brains were studied specifically because the families suspected that football had damaged their loved one. It’s not a random study and it does not attempt to establish a CTE rate.

But the raw data released Tuesday by researchers from Boston University School of Medicine and the VA Boston Healthcare System, in the words of neuropathologist Ann McKee, provides “overwhelming circumstantial evidence that CTE is linked to football.”

For many parents, that evidence will provide more reason to discourage their sons from playing football. For the millions who attend games, or watch them on television, that evidence should remind them of the risk these modern gladiators take for our amusement.

The NFL notoriously spent years trying to discredit the concussion research being done at Boston University; the league has since changed its tone and approach.

The NFL has instituted a variety of rule changes intended to discourage blows to the head and to get players suspected to have been concussed out of play. Last September it pledged $100 million for concussion-related research — $60 million on technological development, with an emphasis on improving helmets, and $40 million earmarked for medical research.

The risk equation will remain. The rules of play can change, but the rules of physics don’t. Football players are increasingly larger and faster. The Vikings’ famed “Purple People Eaters” defensive line of the 1960s and ‘70s would be far too small for today’s NFL. Bigger and faster means more forceful collisions, and no helmet can stop the brain from sliding in the skull.

The athletes preparing for the 2017 NFL season at Blakeslee Stadium know more of the risks they are taking than their predecessors did a decade ago. So should the rest of us.