Scientists at the university's Alzheimer's Disease Center found mice subjected to the same forces as tackle football suffered repeated violent wobbles to the head, which were imperceptible to the naked eye.
Dr Bob Cantu, the "Godfather of Concussion" said a key factor in developing CTE was not the severity of the trauma but "the total amount of hits you took and when you started taking them".
Cantu said impacts received when young came at a greater price than those as an adult, regardless of force, and was adamant there should not be any tackle codes until high school.
"Your neck is weak and your brain isn't myelinated and it's easier to disrupt brain fibres," he said.
READ MORE: The Longest Goodbye: Dylan Cleaver's award-winning series on rugby and the dementia dilemma.
ACC data showed there were more than 34,700 sports claims for serious injuries in 2017 with 11 of those causing serious, life-long disabilities and six deaths.
Of those claims, only 178 were professional sports people. 19,823 were under 18 and 14,733 were classed as other.
League accounted for 1720 of those injuries while there were 7001 in rugby union - the largest number of claims of any sport.
New Zealand Rugby head of medical Ian Murphy said there was still much to learn about the risk-reward of contact youth sport and said his organisation would continue to offer tackle rugby to children, with a continuing onus on technique.
"You're seeing an emerging discussion around non-contact forms of contact sports at younger ages. That's emerging slowly. It's arguably not a bad thing but I think there'll always be a group that likes to play the contact form of games," Murphy said.
Cantu said the numbers of CTE afflictions in NFL players was eye-popping but didn't believe rugby would hit comparable levels.
