As Australia's football codes grapple with allegations of doping and match-fixing, Sunday Night has taken a look at another issue that is threatening the games we love.

Head knocks and concussions have gone hand-in-hand with most football codes for centuries, but the true impact of these brutal sports is only just coming to light.

And as Peter FitzSimmons explains, the initial findings may shock you.

FitzSimmons, himself a former rugby player, has spoken to doctors behind a world first study in Australia that is exploring the effects of concussion on living former players.

Using former professional footballers Greg Williams and Shaun Valentine as examples, the study has exposed the frightening link between contact sport and brain diseases like dementia.

"Amazing stuff on #sn7 with long term brain damage," tweeted current Geelong AFL midfielder James Kelly on Sunday.

"Probably have to ask if it’s at the end of the day it's all worth it??".

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