Under the NAB Cup rules in those rounds, the interchanges at quarter-time, half-time and three-quarter time will not be included in the cap.
Interchanges remaining in the cap from the previous quarter will not roll-over into the next quarter.

In round one of the series however clubs will be able to have six players on the interchange and rotations will be unlimited.

The NAB Cup trial of capped interchanges follows the AFL Commission decision in October to defer any change to the current three interchange, one substitute system that has been in place since 2011.

At that meeting the AFL Commission agreed in principle to an interchange cap – where the number of interchanges per quarter is limited – but wanted further analysis and data collection to take place before accepting a recommendation for change.

It is understood the method to be used to record the number of interchanges and inform clubs of the count during each quarter is still being bedded down but will be in place once the series begins.

Adelaide midfield coach Scott Camporeale told AFL.com.au he welcomed the trial but admitted the defending NAB Cup premiers had not spent much time in the pre-season considering how it would manage with limited rotations in those games.

"It will be interesting and will give us a bit of a heads up as to what it might look like if they do bring it in permanently, but the biggest thing [in the NAB Cup] will be monitoring minutes and the players' workload in each area," Camporeale said.

Port Adelaide's director of coaching Alan Richardson said while the teams lost a little flexibility because of the cap he was all for such trials in the NAB Cup.

Richardson said clubs would use the system in a productive manner anyway.

"Strategically we're pretty keen for guys to be able to play multiple positions anyway," Richardson said. "The obvious thing that will happen is that instead of rotating [off the ground] guys will go forward or back."

The capped system to be used in the NAB Cup series also contains a provision for a medical assessment to be made without an interchange being recorded.

When a club official advises an AFL interchange official that a player has left the ground for a medical assessment, no interchange will be recorded but the player being assessed will be off the ground for 15 minutes of playing time.

The replacement player in that instance will be one of the three interchange players rather than the substitute player.

The provision was considered sufficient to allow doctors time to assess players suspected of concussion and trial some of the practical implications of the decision-making process in those instances.

The suggestion made in 2012 that an injury substitute be introduced remains on the agenda with the AFL Medical Officers Association resolving at their November meeting to submit to the AFL a proposal as to how an injury sub or concussion sub might work if it was introduced in 2014.

The association is most interested in exploring what options are available if the three interchange and one substitute system remains unchanged beyond 2013. Introducing a 'concussion sub' is considered easier to implement in practical terms at this stage under a capped system.

They have already begun considering the question with AFL Football Operations.

"It's probably less urgent as an issue if they [the AFL Commission] put a cap on interchanges but if the current system remains in place then we will be exploring the idea of being able to still use [a concussion sub]," Dr Hugh Seward said.

And if it's a tie in the NAB Cup Grand Final, and two five- minute periods of extra time is played?

Each team will be able to make a maximum of five interchanges for each period.