The change is seen as an appeasing measure following a recent clampdown against swimmers considered to be pushing the boundaries of previous rules.

"In medley swimming, on the freestyle section, the 'swimmer must be on the breast except when executing a turn," reads the new rule.

"The swimmer must return to the breast before any kick or stroke'.

"Moreover, each of the strokes must cover one quarter of the distance."

Previous rules stipulated that a "unique stroke" must be swum from the first three backstroke, breaststroke and butterfly legs.

However. most swimmers, turn off the wall in a way considered to be backstroke to begin the closing freestyle leg.

This was rarely punish until recent years, where leading swimmers such as American Ryan Lochte have pushed the limits by kicking for several metres on their back before beginning the stroke.

Another American in Ella Eastin was disqualified from the women's 400 metre individual medley at the United States World Championship trials for doing this.

But the new rules, due to come into operation on September 21, will permit this so long as they revert to go "on the breast" before beginning a stroke.

Other changes approved during the meeting included a rule banning underwater kicking on the side in a butterfly race.

Timing to 1/1000 of a second is no longer a possibility, it was also decided, seemingly increasing the chance of ties in races.

World records will also only be deemed legal if they are established in water with less than 3gr/litre of salt.