(CNN)Professional rugby union players can experience a decrease in blood flow to the brain over the course of a season due to the effects of collisions, a new study has found.
The study, undertaken by researchers at the University of South Wales (USW) and published in the Journal of Experimental Physiology on Wednesday, examined 21 players during a single season comprising of 31 games.
All of the participants -- 13 forwards and eight backs -- also experienced a decline in brain function, which included the ability to reason, remember, formulate ideas and carry out mental tasks.
According to a press release from USW, the study is the first to highlight how repeated contact sustained in rugby games and training can lead to reduced blood flow to the brain in one season.
"What we're focused on here is the contact events as a result of scrummaging, rucking, mauling, tackling collisions," Professor Damian Bailey, one of the authors of the study, told CNN Sport.
"We feel that it's the recurrency, the chronic exposure ... that ultimately culminate in causing an impairment in blood flow, and as a result, fuel delivery -- oxygen and glucose delivery -- to the brain, which in the long term, we feel can contribute to an impairment in cognitive function."
The players involved in the study were members of a team competing in the United Rugby Championship -- a professional league made up of clubs from Wales, Ireland, Scotland, South Africa and Italy.
According to Professor Bailey, those involved were exposed to 11,000 contact events per season, per player. He advocates for increased screening of rugby players to better understand the effects of these repeated collisions over the course of a career.
"We religiously measure strength, we religiously measure cardiorespiratory fitness, but we never assess brain fitness or health," added Professor Bailey.
"We're still at the very beginning of trying to understand what happens to the rugby player's brain, but I think there's sufficient evidence for us to be a little bit concerned and to look at ways of improving the safety, not just in-game, but out-of-game as well."
Next steps
The effects of repeated hits to the head in American football are well-documented. In 2015, a class-action lawsuit was settled between the NFL and more than 5,000 former players that provided up to $5 million per retired player for serious medical conditions associated with repeated head trauma.
In rugby, the impact of collisions in the sport has emerged more recently.
Last year, a group of former players put forward a legal case against rugby's governing bodies over the issue of degenerative brain disease.
Some of the former players involved had been diagnosed with early onset dementia and probable chronic traumatic encephalopathy (CTE) -- a progressive, degenerative brain disease caused by repeated hits to the head -- in their early 40s.
Tackling concussions with Alistair Hargreaves 03:30
Elite rugby teams operate a Head Injury Assessment (HIA) protocol during games to identify and manage the impact of head injuries, which has been in place for a number of years.
On Tuesday, World Rugby, the game's global governing body, said welfare "always will be our number one priority."
A statement added: "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."
But Professor Bailey says the game's current response to concussion is "reactive."
"The big question for this research really is just laying the foundation stone for trying to understand what happens to the retired professional rugby player's brain in later life," he added.
"The brain aging process -- is it accelerated (in rugby players) relative to ... (those) who don't engage in rugby?"
The USW study also found that cognitive function decreased to a greater degree in forwards compared to backs, and that concussion incidence was three times greater in forwards than backs.
