But the real reason for the tireless physical work may surprise.
"It's not just about improving the strength side of things with weights, but also making the players better runners," North's Strength and Conditioning Coach Dan Meehan told NMFC.com.au.
"It also helps improve their contested possession and one-on-one marking contests."
While many would see the work that goes into the top half of a player's body with their muscular physique, it's elsewhere that the biggest gains are made.
"A large part of leg weights is actually to improve the players' running efficiency, their ability to accelerate and change direction so they're able to produce more force to do those things."
With the group returning to Aegis Park after an intense three weeks in Utah, Meehan has already noticed some big improvers.
"Supporters would be very glad to hear Ben Cunnington got even stronger again," he added.
"Cam Delaney has improved a lot too. He's put on a fair bit of size and gotten a lot stronger, and Aaron Black as well.
"Robbie Tarrant came back in really good shape and took out the bench-press competition on his return so he was pretty happy."
While several Roos' underwent minor post-season surgery, their time on the sidelines didn't go to waste.
"Certainly for Aaron Mullett and Cam Delaney who've been in rehab it's one of the positives for them. While they haven't been able to join in with the running, they've been able to focus on putting on a little extra weight through muscle.
"Kieran Harper has certainly gotten a lot stronger too while getting his ankle right and improving his running. Mason Wood is another one who probably improved a lot in the off-season since he's been in rehab. That's the silver lining for those guys."
Meehan says new recruits Kayne Turner, Trent Dumont and Ben Brown will learn a lot about elite training in their first few months as AFL players.
"I think you'll see a very quick progression with Kayne (Turner). We'll be trying to put a lot more weight on him a bit quicker than we usually would.
"He's certainly on the slight side but he's very hard at the ball which is pretty impressive for someone who's only 67 kilograms.
"Trent (Dumont) has got a bit of work to do with his upper body but he's very strong in the lower body which is a really good start for someone in their first year.
"Browny is a bit better developed since he's been in the VFL system but he's someone who we'll be looking to put a fair bit of weight on. He's about 200 centimetres and he's only weighing in the high 90's."
The hours the players spend in the gym will ensure North's developing list is well prepared to take on season 2014.
"It's not just about improving their size, strength and power, it's about making them more durable which will prevent injuries. We want to be one of the strongest, most powerful teams in the competition."
