Penrith Panthers forward Trent Merrin has relished a full pre-season under his belt for the first time in two years after declaring he carried too much weight in 2017.

Merrin, who represented Australia in the 2016 Four Nations, was disrupted by a calf injury 12 months ago and admitted he struggled to catch up on his fitness as the year progressed, piling on weight and struggling to contain his usual mobility.

The 28-year-old dominated in attack during his first season at the club in 2016, but was noticeably down on key statistics – in particular game time – during his second year at the foot of the mountains.

"This [pre-season] has been the best I've looked in my career," Merrin said.

"I've put a big effort since missing out on the World Cup and made it best for me. I've put myself in a good position but it's at a point now where I need to translate that into good footy.

"Coming off the Four Nations last year and doing my calf in pre-season just set me back a lot. It's hard once the season starts to catch up on a few weeks. It was something I tried to get on top of the whole year last year and it was tough to maintain."

According to NRL.com Stats, Merrin's minutes in 2017 slumped to an average of 55 per game – down on his 67-minute average the previous year, where he was arguably performing at a career best to earn selection in Mal Meninga's Kangaroos squad at season's end.

Meninga remained loyal to Merrin in May by selecting the Shellharbour junior in Australia's 30-12 Anzac 2017 Test win over New Zealand, despite a lack of form heading into the game.

"It comes down to my body shape and all that last year too," Merrin said.

"I was carrying a few too many kilos and I couldn't get around the field the way I'd like to – use my footwork and put myself into positions to make that second phase.

"I've done a lot of homework on myself over the last year and coming into this year it's given me a lot of clarity.

"I'm a big believer of pre-season and believe it's sets you up for the year. You really need one under your belt to handle the way that we play."

The former St George Illawarra Dragons forward remained hopeful an improvement in club form could earn a recall in both the Origin and international arena in 2018, with Merrin in no mood to give up on the prospects of a representative return.

Merrin was a part of the NSW Blues setup for five-straight seasons playing in 13 games – including the state's successful campaign in 2014 – only to be overlooked by former coach Laurie Daley for the past two years.

"I never will [give up], it's something that always drives me," Merrin said of his Origin ambitions.

"As a kid you dream of being in that Blues jersey. I played in 13 games and it's something that I want to continue to do.

"I'll leave my footy up to it now."