It comes amid national debate on the diagnosis and treatment of concussed players. At an amateur level, stand-down periods are mandatory for concussed players.
For the study, 38 senior players from Hutt Old Boys Marist wore mouthguards fitted with accelerometers to measure the pressure on the head after impact.
During the 2013 season, which spanned 19 games, 20,687 impacts greater than 10g - 10 times the force of gravity - were recorded, and the average force was 22g.
An F-16 pilot completing a roll is exposed to 9g over a longer period of time, while a car crash at 65km/h is about 35g. The largest force felt bya player in the study was 164.9g.
Forwards (13,340) received more impacts than backs (7347). First five-eighths - in the backs - had the most impacts per match (117).
Their fellow backs at second five and centre suffered the least (32) but - with hookers - were exposed to the largest force per impact.
Players had an average of 77 impacts to their heads each game, or 1379 a season, more than previous studies have found in American high school football (16 to 29 a game or 520 to 625 per season) and American college football (nine to 13 a game or 414 to 1400 a season).
Analyses of American football teams had established an injury tolerance level of 95g.
The New Zealand study recorded 181 impacts greater than that, though the relevance is not clear as American football players wear helmets.
Dr King said that two concussions observed during the study occurred after impacts under 95g, showing the indistinct relationship between the force of impacts and whether they resulted in injuries.
He said the study was only the first of many that needed to be done if New Zealand was to get a clearer picture of the effects of head impacts in rugby, because it focused on only one team at one level, for one season.
"We need a lot more studies at various levels to be able to say 'this is what's going on on the footy field'."
- Christchurch Star