NORTH Melbourne vice-captain Drew Petrie has dropped about 4.5kg since last year's preliminary final in a bid to keep up with the ever-increasing running demands on key forwards.

Petrie weighed about 101kg when North lost its second consecutive preliminary final this year, going down to West Coast at Domain Stadium by 25 points.

The 33-year-old told reporters on Tuesday that he had made a conscious effort to lose weight over the off-season to give himself the best possible platform for next season.

"I'm just trying to be a little bit lighter this time of the year and make sure I'm running really well, not carrying any extra weight that I don't need," Petrie said.

"Then over the next couple of months, I'll hopefully put on some strength in the gym."

Petrie's fitness kick reflects his belief that he still can improve as a player even as he prepares to enter his 16th AFL season.

Shaun Atley, Jamie Macmillan, Drew Petrie, Lachie Hansen, Ben Cunnington and Sam Wright at Station Pier in Melbourne on Tuesday. Picture: AFL Media

Petrie is just as confident fellow North veterans Brent Harvey, Jarrad Waite, Nick Dal Santo and Michael Firrito can continue to improve next season.

Some commentators think the fact these key players are nearing the end of their careers means that North's premiership window is closing fast.

But Petrie is confident North's ageing list can contend for the 2016 premiership, while it also has an exciting batch of youngsters emerging.

"I think the sides that have won the premiership in the last decade have had a lot of experience in their side and the experienced guys that we've got all want to improve and all have improvement in us," Petrie said.

"You don't continue playing footy if you don't think you can improve anymore, so we all know we can get better.

"Just looking around the locker room so far in pre-season, it seems as though there are a lot of young kids there as well.

"So while the stats say we're a very old side – that is the formula to help win a Grand Final – but we've got plenty of youth coming through as well."

To have a realistic shot at next year's flag, Petrie said North had to cement a top-four spot at the end of the home and away season.

To do that, he said the Roos could not afford to have the type of slow start to the season that has plagued them under coach Brad Scott.

Last season, for instance, the Roos needed to win seven straight games late in the season to recover from a 6-7 start and make the finals.

"We've got to make inroads in the first 10 weeks of the season and not leave it until the last minute again," Petrie said. 

Petrie also put the acid on himself to make a faster start to 2016, describing his first eight weeks of 2015 as "really ordinary".