Anthony Joshua, Dillian Whyte and Oleksandr Usyk offer sparring which can be physically exhausting or relentlessly brutal, says rising contender Fabio Wardley.
The unbeaten 26-year-old has already traded punches with the world's top heavyweights, having been invited to test his skills and durability as a sparring partner for Joshua, Whyte and Usyk.
Wardley has provided insight into high-level sessions with the sport's best technicians and most hurtful punchers...
Do you follow strict instructions in sparring?
The only things I've been told to do is either pick it up, in terms of aggression and what you're putting into the spar or turn it down. Keep it lighter, more technical, keep it sharper.
They are the only indications I've ever had, because some camps like you to go full out, properly stuck in, and treat it like a fight really. Other camps want you to make it more of a technical spar than anything else.
Which fighter told you to raise the aggression?
The biggest one for me was Filip Hrgovic. When I was out in Miami, he wanted it like this was the deciding factor for both of our lives or something, which is fine by me. It's nice to be able to get stuck in properly like that.
Some people don't want you to and quite rightly, people don't want to get injured and whatever else, but sometimes it's nice to let it all go.
Are you asked to mimic a certain style?
It's the fact that they've chosen you in the first place, they've already assessed your style.
I like to make sure my style fits. I've even had cases in the past where I've been offered sparring with high-level people and I've said, 'Take a look at a video or two. I don't think I replicate or fit the kind of fighter that you're looking for.'
Which fighter was that?
It was Peter and Hughie Fury. I think he (Hughie) was going to fight Povetkin and they called me and said they wanted me for sparring.
I said, 'I'm buzzing, I'm happy to come down and do whatever, but I just don't think I resemble him very well.' I sent them links to some of my fights.
They checked it and Peter came back and said, 'Thank you for being honest, thank you for doing that. We've had a look and we don't think it fits.'
Would Joshua work on specific tactics?
I just think he used different sparring partners for different styles. I was in, then Gerald Washington was in. Bryant Jennings was in. We're all a little bit different.
As opposed to just getting stuck into fighting against one style, he was using people along similar lines, but slight adjustments that he can then in his head pay attention to and learn to overcome.
Did AJ show any sparring secrets against Pulev?
The one thing that I have said that when I came out of that spar, which I was impressed by, was how light and fluid he was on his feet, especially for someone of that size.
You see a lot of it in the Pulev fight, where he just takes these little half steps in, gets his work, and then a little half step out. It's really short and sharp and quick and crisp, but it works very well.
It was something I was quite surprised at, because I've sparred big guys. I'm used to being the one that's quicker and sharper, and lighter on my feet. There were times where he was matching me, with things like that, and I was quite surprised by that, because I didn't expect that to come from such a big guy.
Does Usyk have a different approach to sparring?
With Usyk, I think the pace was a lot higher. With Joshua, I could control the pace a bit, if I wanted. If I wanted to take time and be in control of things, when we were engaging, when we weren't engaging and stuff, I could.
But with Usyk, he is in control, he is the one on the front foot, pressing you where he wants you to go. He is the one actively throwing the punches.
Nine times out of 10, you are reacting and you are returning. Especially with Usyk, I didn't find any gaps where I could take control of the pace of the fight, or get my work off for free without getting something in exchange.
What's it like to spar with Whyte?
I always end up with some sort of bruise, or some sort of knock, or whatever else.
It's because we know each other so well, that there's more of that relaxed side to it where we know to take a few rounds, to maybe make it a bit more technical, and we work on some things between ourselves. Then we have a few rounds where we proper have a go at each other and get stuck in, just because that's what both of us love.
Can it be brutal?
Some of those sparring sessions have been horrible. I've come out with bruises, bumps and scrapes. Me and him have done 10, 12 rounds together, just on the bounce.
He'll meet you there and then. That's where it can get messy.
There's a fine margin between getting fully stuck in, and going really hell for leather as you can go a touch too far. When it's someone like Dillian, who is very experienced and someone I know very well, we never hit that line.
I've witnessed it and I've watched and I know Dillian well, I know what he's like. If it gets to the point where you are now trying to take the p***, he won't back down at all. He'll meet you there and then. That's where it can get messy.
How has sparring improved you?
I always find something new in myself that I need to work on, because there's things that you do in other sparring that doesn't work on certain styles.
I always say it's about putting different pieces together in a puzzle and finding what fits against what, because each person you get in the ring with is a different kind of puzzle.
It's just about sparring a bunch of different people and taking those little bits of information and remembering them, and using them the next time around.