Joe McCarthy has a big frame and a big appetite.

The Leinster lock is over 6'4" and 19 stone, but he's feeling sharper than ever after a gruelling pre-season that emphasised reaching optimum physical fitness.

Ireland head coach Andy Farrell is demanding very high levels from his players when it comes to aerobic capabilities and sheer power.

McCarthy is embracing the challenge. Ahead of Friday night's Nations Championship clash with Argentina, he revealed one of the secrets behind his own conditioning; wrestling with younger brother Paddy.

"I'm always trying to get a bit faster, I don't think you can ever be fit enough as a rugby player, especially for international rugby," McCarthy told RTÉ's Inside Sport.

"It is always like a big step up from club rugby. You have to think faster and you have to move quicker because the athletes are better and the games just seem to go to a higher level.

"(In Leinster pre-season) we did a tonne of wrestling in between running and things like that. So a lot of one-v-one wrestling, which was quite tough. That completely saps the energy out of you. We've got some big guys in Leinster at the moment.

"I think a lot of us are feeling in good shape after that pre-season."

McCarthy was pitted against the likes of James Ryan, Ryan Baird and Tadgh Furlong - "a big unit to shift around" - but had an edge when it came to the match-ups.

"I mainly just wrestle with my brother Paddy," he said. "My brother Paddy's actually quite a good wrestler. I remember in school, he did a bit of jiu jitsu or whatever, things like that. When he trained for his Senior Cup he was always quite good at that. I'd always have his number, but he was a good challenge as a younger brother.

"We wrecked the house a good bit when we were younger. We've gotten to a size now where we don't do that too much anymore!"

Food was plentiful in the McCarthy household. It takes a lot to fuel a couple of budding professional rugby players, and there was no skimping when it came to stocking up the fridge.

"We definitely ate a lot," added McCarthy. "We'd always have like 24 eggs, 14 litres of milk in the shopping cart. We just always ate a lot and we ate well. My mum cooks really well. She always cooks a massive Sunday roast for us. My mum always preached good quality food should be a staple of what you have. She really was big on that.

"I wouldn't meticulously have a certain calorie target, but definitely would be eating around 5,000, 6,000 a day I'd say on training days. I always wanted to be a bit of a bigger athlete and make that a point of difference."

Ireland take on the Pumas at Aviva Stadium and then Fiji the following weekend.

The big one however is against South Africa, who come to Dublin on Saturday 21 November.

With the World Cup coming in 2027, it's a chance for Ireland to measure themselves against a contender.

"You can have all these plans and intricate moves to move the ball and get them uncomfortable, but there's a certain level of... you're going to have to properly borrow physically and have that mindset to be physical and win every battle," said McCarthy

"You probably know you won't win every battle, but just being able to get back into them. So we'll do that. I know we're working very hard on our scrum and maul, which are going to be key areas of the game.

"You only have a couple of weeks in international windows to bed it in, but everything we're doing in terms of our gym work, we have more orientated around their scrum or maul and how that translates onto the pitch.

"We'll do that as well and try and put that in place in the Argentinian and Fiji games. It'll be tough, but I think it's a challenge that everyone's relishing because they're obviously number one in the world now, but I think we're kind of relishing that and we'll have to be at our best to get a win."

McCarthy is buzzing for an important autumn, and then a massive 2027. The World Cup takes place in Australia in a year's time and already there's an edge to preparations.

"It does feel like a different kind of season," the 25-year-old admitted. "When you've got the World Cup at the end, it feels like a like a bigger task, but it's quite exciting as well. We'd a big talk pre-season about trying to get fitter, faster, stronger, and in the best shape we've ever been.

"It starts with Argentina is how we're looking at it, try and get a proper performance and put a bit of work in the bank and build a bit of confidence going into the year.

"The buzz that the Irish fans give you when you're coming to the stadium, you can really feel the good energy. Those evening games, everyone's had the whole day building up towards it and getting involved.

"They're literally some of the best days of your life."

Follow a live blog of Ireland v Argentina on Friday (8.10pm) on rte.ie/sport and the RTÉ News app, and listen to live commentary on RTÉ Radio 1's Sport Extra