Professional rugby players who play more than 25 matches in a season are more likely to suffer a concussion than not, according to a newly released study.
The report recommended "limiting the number of matches players are involved in during a season to 25".
The best professional New Zealand rugby players tend to play close to that number every year.
Beauden Barrett, for example, played 15 times for the Hurricanes in 2017 (once as a substitute) and 10 times for the All Blacks. He missed the final test of the year through concussion.
Aaron Smith also played 25 matches across Super Rugby and the All Blacks. Lock Sam Whitelock, who captained the Crusaders, played 26, including nine for the All Blacks. Hooker Codie Taylor played 27, although seven of those were from the subs bench.
The research, led by James Rafferty of Cardiff Metropolitan University and published in the British Journal of Sports Medicine, included the sobering conclusion return-to-play protocols "warrant investigation" after it was discovered players were 38 per cent more likely to be injured again shortly after suffering a concussive injury than those suffered non-concussive injuries.
Those secondary injuries apply to all areas of the body, not just the head.
The study took place over four years, from the 2012-13 season to the 2015-16 season, using the injury surveillance database of the Welsh Rugby Union, which monitors the national men's side and its four professional clubs – Cardiff Blues, Dragons, Ospreys and Scarlets.
The data showed 2441 injuries to 367 players, from a total pool of 429. Some 1602 of the injuries occurred during matches, 514 during training and 325 during other activities.
Concussion was the most common injury (10 per cent) and although the incidence increased over the four seasons, the severity of concussions did not.
The data saw concussion incidence increase from 7.9 injuries over 1000 player-match-hours, to 21.5, a significant rise.
Although it has been suggested the emergence of Head Injury Assessment protocol has led to a rise in the numbers because previously unreported concussions were now being picked up, this should have seen a spike only for the 2014-15 season, the first played under the protocols.
"However, the continued rise in incidence in the 2015-16 season implies there are additional factors other than stakeholder awareness that contribute to the increased concussion incidence," the report noted.
The report was published on the same day as a study into Accident Compensation Corporation claims for New Zealand's five major sporting codes.
That report, lead authored by concussion expert Dr Doug King, looked at claims from cricket, netball, league, rugby and football from 2012-16.
The injuries were analysed by severity – either moderate-to-serious, or serious.
The study showed rugby still has easily the most claims and highest costs to the taxpayer than any other sport. Concussion claims increased over the term of the study, with the greatest increase coming in netball, supposedly a non-contact sport.
Over the five years, rugby resulted in 25,226 moderate-to-serious injury entitlement claims, costing more than $267 million. The national sport also had the highest number of serious injury entitlement claims.
The data did not include injury incidence figures, and did not analyse the reasons for the increases in claims.
The Concussion Club
Of the 55 players who pulled on an All Blacks jersey in 2017, 17 have suffered a concussion in the past calendar year. They were: Sam Whitelock, Beauden Barrett, Sonny Bill Williams, Sam Cane, Dane Coles, Ben Smith, Ryan Crotty, Brodie Retallick, Kane Hames, Ardie Savea, Waisake Naholo, Wyatt Crockett, Tawera Kerr-Barlow, Matt Todd, Nepo Laulala, Aaron Cruden, Malakai Fekitoa.