INJURY-plagued Roo Robbie Tarrant is finally back in full training as he prepares to switch back to defence in 2015.

Tarrant had season-ending surgery in June to repair a stress fracture in his tibia that restricted him to just one VFL game and one AFL match last year.

On Thursday, the key-position player completed his first session back with North's main training group, taking part in game-sense drills.

It was a significant step for the 25-year-old who has been carefully managed by North since he started running again last September.

Starting off on the Alter-G treadmill - which reduces the stress on a player's legs with a weight-bearing harness - Tarrant progressed to straight-line running outside, gradually increasing his intensity before finally incorporating lateral movement.

Tarrant told NMFC.com.au his pre-season had gone smoothly so far, saying he had not pulled up sore after training for three or four months.

"It's probably the most sessions I've done in a row for a good four or five years," Tarrant said.

North football director Geoff Walsh said last October the Roos would play Tarrant in defence this season as they seek to identify someone capable of manning powerhouse forwards such as Tom Hawkins, Travis Cloke and Lance Franklin.

The former Bendigo Pioneer played most of his junior football in attack and has been used as a key forward by North for the past three seasons, but the backline is not completely foreign to Tarrant.

He made his AFL debut in defence in 2010 and remained there the following season, playing seven games for the Roos in a key defensive post in 2011.

Tarrant said he was still readjusting to playing in defence but had some handy teachers at North that he could lean on.

"I'm learning the role now and I'll jump in with Scotty Thompson, 'Narni' (Nathan Grima) and Lachy (Hansen), and try and learn some things off them," Tarrant said.

"I'll probably look to play on the bigger sort of forwards. I still back my running in against most (players).

"I know the forward role relatively well now so I can always flick back forward, but I'm going to give it my best and hopefully I pick the defensive side up pretty quickly and that works out."

Tarrant was taken by North at pick No.15 in the 2007 NAB AFL Draft but a nightmare run of injuries has limited him to just 39 senior games.

Most notably, he had three shoulder reconstructions in his first two seasons at Arden Street, while his tibia injury also disrupted his 2013 season, sidelining him for nine consecutive games early in the year and severely restricting his ability to train on his return.

"I haven't just been injured for the last year, it's been a seven or eight-year period where I've struggled to go through the whole year without getting injured," Tarrant said.

"I'd love to get to as many games as I can individually, but the most important thing now is I think we're in a good window for some team success and I just want to be a part of that."