Rugby coaches are being urged to concentrate on improving players' neck strength in a bid to avoid debilitating concussions.
A ground-breaking New Zealand study has found players with weaker and uneven neck strength are more vulnerable to severe impacts that may cause concussion.
The experiment by Otago University's Dr Hamish Osborne and Research Fellow Dr Danielle Salmon used bluetooth sensors behind the ears of 23 players in the Otago Mitre 10 Cup rugby team to measure acceleration, or g forces, during impacts in five games.
The neck strength of each player was also measured using especially designed equipment.
Salmon said the weaker the neck the more severe the damaging "whip-lash" type movement. A higher acceleration force was also recorded.
"We found players with stronger necks had lower acceleration or whip-lash like movement.
"The stronger you can make the neck the less the head accelerates - it controls the brain's movement against the skull."
Salmon said coaches at all levels needed to put as much value on neck strengthening exercises as they did fitness and skills.
The study revealed props sustained the most frequent and strongest head accelerations force, while those on the wing had the fewest hits but those they did receive were often powerful.
The data showed the players on average sustained 48 impacts per game.
"When we break down the game to specific events, we observed that the average head-acceleration force for a carry was 45g. For a tackle it was 42g and for a ruck, 31g."
Research in the United States suggested concussion happens in the range of 68 - 106 g of force.
Humans are able to bear localised g-forces in the hundreds of g's for a split second, such as a slap on the face. But continued g-forces above about 10g can lead to permanent injury.
New Zealand Rugby and Otago Rugby Union already include neck strengthening as part of their coaching but said they would now increase the focus.
NZR Medical Director Ian Murphy welcomed the research and said it would update information sent to coaches.
"We regularly update our Rugby Smart programme and we will be adding to our work around neck strength, including our messaging to include the potential link to reducing concussions."
Otago Rugby boss Richard Kinley said anything that helped improve the health and safety of players would be taken on board.
"Neck strengthening has always been a focus but looking at the findings if there needs to be more time spent in developing neck strength we will do this."
Last month the Herald on Sunday published figures showing the amount claimed for injuries suffered while playing rugby had increased every year since 2011.
It peaked at more than $76 million in 2015.
The ACC figures show concussion injuries have steadily increased from 1620 in 2012 to 2410 in 2015.
The Herald has been investigating the potential link between head injuries suffered in rugby and long-term cognitive difficulties.
In March last year it was revealed at least five of the Taranaki Ranfurly Shield squad of 1964 had died or were suffering dementia-related illnesses, which the families believed could have been the result of multiple concussions suffered in their playing days.
Four of the 1967 All Blacks who toured the UK had suffered the same fate, including legendary flanker Waka Nathan.