Head injuries in football can cause unexpected consequences years later

"Players in sports need to be respected as humans, not merely replaceable beings for our entertainment," she says.

What's more, the longterm effects of repeated head injuries may not surface until years after the injury.

An assistant professor of philosophy/humanities and adjunct professor of kinesiology and integrative physiology at Michigan Technological University, Johnson cites Chris Henry, former wide receiver for the NFL's Cincinnati Bengals, who died of injuries in a car accident after years of dangerous and illegal behavior. An autopsy revealed that Henry had developed chronic traumatic encephalopathy.

It is believed that one of the causes of CTE is sub-concussive impacts, the kind of ordinary hits that athletes routinely take in the course of play," Johnson says. "CTE is a condition that can't be diagnosed, doesn't have clear symptoms and can't be treated."

So, post-concussion guidelines don't do anything about CTE, she adds. How many more players are similarly affected is unknown.