According To The Concussion Study, A Player's Cognitive Function Can Deteriorate After Just One Season Of Rugby.

University of South Wales research tracked professional rugby teams over a season, testing pre-season, mid-season, and post-season players. It is published in the September issue of the Journal of Experimental Physiology. 

They say more research is needed on the long-term effects.

Their study, viewed exclusively by the BBC, found that a team of professional rugby players found decreased blood flow to the brain and cognitive function - the ability to think, remember, formulate ideas, and mental gymnastics - in just one season.

The document also shows that they cause the shaking, repeated contact, or shock caused by rugby and the observed reduction in players. Former Lions and Wales player Shane Williams himself suffered a head injury while playing and says a player's risk of injury increases when he is tired.

He joins calls for limiting substitutions because new players coming onto the field can do more damage.

In this new study, 200 former players - Welsh and English, male and female, professional and amateur - and Ryland have filed lawsuits against the game's governing bodies World Rugby, Welsh Rugby Union, and Rugby Football Union.

Some of these former players have been diagnosed with early dementia, and authorities say they failed to protect them from the risk of concussions and blows to the head.

Welcoming the new study, World Rugby added, "World Rugby has recently committed to double our investment in player wellbeing, as well as surprising new research and initiatives." Former Welsh winger Williams endured some of the powerful strokes and headers that impacted his career, nothing more than a smack but a legal move by South Africa's Bakkies Botha in 2004.

"It was the blur that changed after that - looking at the players, then seeing the family members in the stadium, I don't remember - it was almost like being dwarfed for a few hours, and the next thing I was sitting in reception and thinking: 'Oh my God, what happened at the stadium. There?

Seeing the effects he's had over the years, Williams doubted whether his brain was affected by the game.

"I always ask myself, 'Has my memory deteriorated with my age?'

Head injury assessments or HIA logs, which are now common in games and designed to help decipher whether a player has suffered a concussion, were not practical until 2015. Williams believes that if the same incident had happened in 2004 - and if he had known what he knows now - he would have left the field.

"I think a lot of it was education - if I were hit like this today, I would know right away that something was wrong," he said. "People still ask, 'Am I going to change the way I play? Am I not going to play?' "I won't have it because I play a game I like."