Rugby chiefs on Friday announced that a new law designed to improve player safety in the scrum would be trialled during the Six Nations, which starts next month.
World Rugby wants to discover if a minor adjustment can limit the number of collapsed scrums and resets, while also relieving the force on the spines and necks of hookers.
Both hookers must now ensure one foot - the "brake foot" - is extended towards the opposition during the crouch and bind phases of the engagement sequence. A free-kick will be given if the brake foot is not applied.
World Rugby chief executive Alan Gilpin said: "We want rugby to be the best it can be for those playing and watching the game and this trial will enable us to understand whether we can positively impact both game and welfare outcomes.
"This builds on voluntary adoption by teams and greater vigilance by match officials in recent elite competitions and we would like to thank Six Nations Rugby and all the participating teams for embracing the trial and we look forward to seeing the results."
Connacht and Ireland hooker Dave Heffernan, who was involved in player consultation, said: "From talking to other hookers, axial loading seems to be causing neck-related issues and while this trial is welcome, it needs to be enforced by referees for both front rows."
Axial loading, when front row players – primarily hookers – lean their heads onto opponents' shoulders, placing pressure through necks, is outlawed but has not been completely eliminated.
The Six Nations starts on 5 February, with Ireland taking on Wales in the tournament opener.