Image copyright Getty Images Image caption England's World Cup winner Jonny Wilkinson replaced during a Six Nations game

Limiting replacements in professional rugby games could reduce injuries by forcing players to be lighter and faster, the WRU's chairman has said.

Gareth Davies is concerned about the rise in "nastier collisions and nastier injuries".

He told the new BBC Wales Live programme such injuries threatened to damage public perceptions of the sport.

Research has showed a sharp increase in the number of reported concussions.

"If you expect a player to play for 80 minutes, they are going to have to change their physicality and their make-up," said Mr Davies, who won 21 caps for Wales between 1978 and 1985.

"It's one way of reducing the size of players as they will have to be fitter and faster for longer.

Image copyright BBC Sport Image caption Former Wales fly-half Gareth Davies became Welsh Rugby Union chairman in 2015

"Rugby is a totally different game now to what it was, even 10 years ago, with huge physical specimens on the park. That is an area that should be looked at, in terms of substitutions.

"Most players are on a [conditioning] programme now to play 45 to 55 minutes. So you can be bulky. And then you bring on more bulky forwards and backs.

"But if you expect people to be on the park for 80 minutes, unless there is an injury, it could open the game up. People will get fatigued and you'll also have a better chance of a spectacle later on."

Gareth Davies, who became WRU chairman in 2015, said the huge size and power of modern players risked devaluing rugby in the long term.

"I feel that by everyone becoming huge physical specimens that can run 100m in 11 seconds, whether you are prop or a wing, it starts chipping away at the uniqueness of the game," he said.

"Twenty-two years on from the arrival of professionalism, I think we are probably paying the price. It's not the old fashioned tackle round the legs anymore.

"You get the upper body and that's why heads are colliding because strong people are trying to stop strong people."

Image copyright Getty Images Image caption Gavin Henson tackles Mathew Tait of England during Wales' Six Nations win in 2005

Research by Dr Izzy Moore from Cardiff Metropolitan University has shown the number of reported concussions has increased by 172% in four seasons.

The research, which is funded by the WRU and rugby's governing body World Rugby, has also revealed players who play more than 25 games per season are more likely to receive a concussion injury and the overall risk of getting injured in international rugby is twice as high as a regional or club match.

Dr Moore told the programme: "The numbers are high. We need to do something.

"In a contact sport, there will always be some risk. Deciding when the risk is too high is the ultimate question."