Just how difficult is to become a world heavyweight champion? Watch this video of Anthony Joshua training and you might just get a glimpse.

We challenged three gym-goers try to match the impressive workouts of world heavyweight champion Joshua. Could you do any better? Probably not.

Let's not forget, whoever wins tonight will not be the undisputed world heavyweight champion.

That is because fearsome unbeaten American Deontay Wilder, with 40 wins, including 39 inside the distance, holds the WBC version of the title.

He is keen to unify all the belts as soon as possible, as you can see in our interview with him below.

"There will be one champion, one face, one name and he goes by the name of Deontay Wilder," says the 32-year-old American.

WBA and IBF world heavyweight champion Anthony Joshua says there is "a difference between being confident and cocky" as he prepares to face WBO title holder Joseph Parker in a unification fight.

"There are so many opinions and voices, if you keep listening to everyone's opinion how could you believe in yourself.

"In this day and age you have to say how confident you are, but there is a difference between confidence and over-confidence and you can't think 'because I beat him I'm going to beat Joseph Parker'."

Mike Costello
BBC Sport boxing correspondent at the Principality Stadium

The tactic is to be lighter and quicker] for Joseph Parker and I think it's been indicated at the scales when he weighed 16st 12lbs, nine pounds lighter than last time out.

The reason he has come in lighter is that his camp believe that speed and movement might be the key to him causing an upset.

"Welcome to the lion's den," is the atmosphere-building clip from Anthony Joshua shown on the big screens. Now the theme tune to Rocky.

Fantastic stuff.

Everyone is making a prediction, it seems.

You know it is a massive event when you get footage of an animal predicting the result.

Paul the Octopus started the trend at the 2010 World Cup and now we have Shenkin IV - the goat mascot of the Third Battalion, Royal Welsh Regiment.

Watch below as Shenkin IV predicts the winner of the Anthony Joshua and Joseph Parker fight at Cardiff's Principality Stadium.

Dragonborn: Joshua will win. KO sixth round.

Frostyboy4: AJ needs to win in six, if not he's in trouble. Parker has a great chin and probably the harder hitter. I fancy an upset.

Furo: Although Parker has to be respected due to what he has so far achieved, AJ will be too big and too strong for Parker. I predict AJ to stop Parker in the sixth.

A lot of love for that sixth round.

Mike Costello
BBC Sport boxing correspondent at the Principality Stadium

This is the test before the test for Joseph Parker. We know how Joshua will respond to this kind of atmosphere and occasion.

We should bear in mind also how Joshua embraced the occasion at Wembley on his first stadium outing, so there's no reason why Parker can't do the same.

There is far more intensity in the air than for the Carlos Takam fight here.

Promoter Eddie Hearn on Sky Sports: "He [Alexander Povetkin] will be mandatory for the winner of Joshua v Parker, but I've got another heavyweight who wants to fight him in the sumner..."

British heavyweight Dillian Whyte, who lost to Anthony Joshua in December 2015, says: "I'll fight him next. Let's do it, I'm ready."

Let's hear from Alexander Povetkin. He has been talking to Sky Sports: "It was really hard in the first rounds I was trying to get him too much, to feel the distance and then I felt how to knock him out.

"I want to say to people in England and Cardiff who love boxing, thank you so much for such a warm welcome."

This is well worth a watch.

Anthony Joshua has produced some magic moments in his career, but he was left baffled by magician Ben Hanlin, who impressed AJ with a card trick at the BBC Sports Personality of the Year awards ceremony in December.

Keep It Real: Two great fighters, two thoroughly decent blokes, their respective parents must be so proud. May the best man win.

James: I'm looking forward to this fight. No silly trash talk in the build up and two fighters at the top of there game. Lets get ready to RUMBLE...

OohAhCantona: Go on AJ.

BBC Sport has spoken to both fighters before this unification bout.

Briton Joshua says "Parker is in for a fight", while New Zealander Parker is "embracing" the challenge ahead.

Joshua added: "Respect is due because of what he has achieved. Every opponent poses a threat and if I make a mistake they will capitalise."

"I've had 24 fights and enjoyed them all, but this is on another level," said Parker.

Watch what both men have to say in the video below.

Ex-world lightweight champion Anthony Crolla, who won on the undercard: "I think AJ will take it inside six explosive rounds. I think Parker may have a little success but I just see AJ having the heavier artillery."

WBO world heavyweight champion Joseph Parker has certainly been relaxed in the build-up to the main event.

"I think I can cause a lot of trouble with the style, movement, speed, angles and if I can execute my plan I know I can win," said Parker.

"I'm not nervous, not scared, just looking forward to it."

Watch the interview below.

Seven Nation Army by The White Stripes rings around the Principality Stadium 'Oh Anthony Joshua' is the chant that is getting louder and louder and louder.

An incredible atmosphere.

BBC Radio 5 live's Mike Costello and Steve Bunce have previewed the big fight and you can listen along via the link below.

Next up is the main event.

Watch the action from yesterday as Anthony Joshua and Joseph Parker weighed in at Cardiff's Motorpoint Arena on the eve of tonight's unification bout at the Principality Stadium.

Joshua is the heavier of the two fighters at 17st 4lbs 2oz, compared to Parker's weight of 16st 12lbs 7oz.

Bishop Yinkus: Will he now retire from boxing? On this account, David Price should call it a day with boxing.

Luke Reddy
BBC Sport boxing reporter at the Principality Stadium

David Price’s wife ringside has to witness the howls as replays are showed of that knockdown. It was heavy and Price looked unconscious on his feet before it came.

The Russian flag is waved to boos.

Dillian Whyte returns to his seat and says “easy money”. I presume he’s talking about facing Alexander Povetkin at some point.

Povetkin could be called as Anthony Joshua’s opponent soon enough though.

Image source, Reuters