A leading brain injury academic believes rugby union could be "a lot more aggressive" in tackling contact reduction in the sport.
Professor Damian Bailey is co-author of a study by the University of South Wales aimed at understanding how recurrent contact impacts the brain long-term.
Professor Bailey's group spent time with a team in the United Rugby Championship – previously the PRO14 – during pre-season before the 2020-21 campaign, across 31 games and then after the season finished.
Their findings, to be published on Wednesday, included players suffering a blood-flow decline to the brain and cognitive function after just one season.
The latest research follows a launch of legal action by around 200 former players – some suffering from early onset dementia – against World Rugby, the Rugby Football Union and Welsh Rugby Union, claiming insufficient protection from risks due to concussion and head contact.
"I am certainly fearful for the younger kids engaging in sport," Professor Bailey said.
"I want them to be physically active, but we are still unclear in terms of what the recurrent contact incurred over a playing life-span can have on the retired brain.
"I think there is sufficient evidence now for us to start tackling this head-on, and to consider interventions to manage it perhaps better than we are currently are, and for more studies to be supported.
"There is more surveillance, but I think we could be a lot more aggressive in terms of reducing contact in training. We could be much more aggressive in terms of substitutes not coming on fresh for the 'big hits’, and also to be a lot more comprehensive in the way we screen players."
Professor Bailey attended the same Bridgend school as former Wales rugby stars Rob Howley and Scott Gibbs, and he added: "We followed players over a single season, and the focus is to try to understand how over the long term recurrent contact impacts the brain.
"When a professional rugby player playing 15-20 years of rugby at the top end retires, does his brain fare better or worse than an age-matched, non-contact, fitness-matched comparison?
"Being physically fit is the best medicine for the brain. Because players have got this high level of aerobic fitness, it does to some extent mask the impairments if they exist.
"I have worked with professional boxers, and the vast majority of injury to the brain is incurred during sparring and training. It’s not the big hit, the big knockout punch, it is that cumulative exposure, and that is what we think is going on with rugby.
"This cumulative building up of these contact events, this impairs the way brain regulates blood-flow to itself. The brain is a super expensive organ to run – the most expensive in the body to run as far as fuel is concerned – and when we impair that, this is where the trouble starts.
"This is probably the unifying feature of dementia over the life-span that we see this reduction of blood flow to the brain.
"We are not out there to try and stop the game of rugby – we are out there to make it safer"
"You have got super-fit, super-conditioned players, but yet we are seeing the way the brain is regulating flow to itself is impaired.
"Based on taking blood samples from the players, we think that is because we haven’t got enough of the good molecule, which the brain needs, and we think that is because of the inflammation – the mechanical damage – that is occurring as a result of the recurrent contact.
"We are not out there to try and stop the game of rugby – we are out there to make it safer.
"If you watch the sport at the top end, these are big impacts going in. I wasn’t surprised in terms of what we found. My big concern is the guys who are in retirement that are suffering with a poor quality of life."
New lobby group Progressive Rugby, which is backed by leading players and sport doctors, welcomed the research.
"This concerning study is yet more evidence that our wonderful game of rugby is not safe in its current format and needs to adapt to survive," a Progressive Rugby spokesperson said.
"The findings further support Progressive Rugby’s stance that the existing return to play protocol is not fit for purpose, and that a 12-day absolute minimum period should be adopted immediately to help protect players while vital research continues."
World Rugby said it "welcomes all research that can inform and support our recently launched strategy to cement rugby as the most progressive sport on player welfare".
A spokesperson said: "The welfare of the global rugby family is and always will be our number one priority.
"We will always be guided by medical and scientific consensus to inform our concussion education, prevention and management strategies, and to make the sport as safe and accessible as it can be for all.
"World Rugby recently committed to double our investment in player welfare and new concussion research and initiatives.
"We are currently undertaking a wide-ranging evaluation of contact training volume across the game and look forward to the results of the ongoing Otago Rugby Community Head Impact Detection study, which is the largest ever study of playing and training head impacts in men’s and women’s community rugby. Both will inform the further introduction of guidelines and preventative measures that best support the welfare of all players."