South Sydney speed demon Damien Cook has spent his summer rebuilding the "ugly" sprinting technique that crowned him one of the most destructive running No.9s of the last 20 years.

Cook has been conducting weekly private training sessions with renowned sprint coach Roger Fabri, whose clientele includes fellow NRL pace merchants Josh Addo-Carr and James Roberts, having workshopped with the NFL's Dallas Cowboys and Olympic champion Michael Johnson in the US.

Cook, 28, inked a multimillion-dollar, Rabbitohs five-year extension two months ago following a stunning 2018 season, in which he racked up the third most running metres (2330) for a hooker in the NRL era.

Despite being clocked at more than 35 km/h by Telstra Tracker data last year – making him the third fastest man involved in the 2018 Origin series – Cook was initially reluctant to link with Fabri for fear of a brutally honest assessment of his homespun technique.

"I'd been meaning to work with Rog for the last two years or so but I held back a bit because I knew he would say my technique is shit," Cook told NRL.com.

"And he did. He said 'you're fast, but you're technique's ugly, it's all over the place'.

"I knew that, I guess I just didn't want to be told that. But I really enjoy working with him, I understand what he's trying to show me and now every time I go to training I'm still trying to hold that technique and running style.

"He picked it to pieces. I'm too forward in the shoulders. I drive well when I'm moving forward but have no momentum being built from my arms, they're not straight. I don't get enough knee lift, I don't keep my knee at a 90 degree angle.

"And that's why you go to him, to get that edge and get that improvement. He's the best that I know in the country. I'll be going back most off-seasons for sure."

Cook has previously turned to cross-code coaches to gain a competitive edge, wrestling with UFC champion Rob Whittaker as he added extra starch to his defence 12 months ago.

The Rabbitohs rake has also bought into the benefits of breathing training, not dissimilar to the wrestling under water Brad Fittler put his Blues squad through during a team trip to Armidale.

"I've been doing a bit on lung capacity in the pool, a bit of cardio without stress on the legs," Cook explains.

"You might do 50 metres breathing every two strokes and then the next 50 metres every four strokes, then six, then eight, basically lung busters.

Cook: It's going to be a special event

"After each session – I got this from Robbie Farah – at the end of every session just going under water and holding my breath as long as possible.

"We ended up doing a similar thing with Freddie and the NSW team, all about putting your body and lungs under stress".

On the paddock Cook wants to build the wider elements of his game, specifically kicking options and game management as he adapts to Wayne Bennett's revamped Rabbitohs.

He will join a host of the Bunnies big names on deck for John Sutton's testimonial match in this Saturday's trial against Penrith.

Cook, Burgess brothers Sam and Tom, Dane Gagai, Alex Johnston and Cody Walker will all be on deck for the club's return to Redfern Oval with Penrith also naming a strong side.