Anthony Joshua has warned Deontay Wilder and Tyson Fury they risk facing a better version of him if frustrating fight negotiations drag on.
Unified world heavyweight champion Joshua faces Andy Ruiz Jr on 1 June.
The 29-year-old says the bout will showcase evolving methods he began to use after beating Wladimir Klitschko.
“I’ve got through with strength, guts and heart,” said Joshua. “I’ve got away with mistakes. I realised I couldn’t continue my journey like that.”
“For the last two years, hand on heart, with my team, we spend so much time doing things outside of boxing, things that can drain me.
“How do we now train smart to become smarter in the ring? Less quantity, more quality. It didn’t happen over night. It has taken two years to implement it and this is the first camp we are really seeing it.
“Look at my last fight against Alexander Povektin. I was ill, tired, had a flu, had a headache. I was going through changes. It will be interesting as this is the first time I can express these things.
Failed talks with both parties led to Joshua’s team opting to tackle a US breakthrough with his next bout, plans that were hampered briefly when original opponent Jarrell Miller failed drug tests.
American Ruiz has 32 wins from 33 fights going into the Madison Square Garden bout.
Joshua admits he sits in an awkward position in striking the balance between showcasing the refined boxing skills he has worked on, while ensuring a “devastating” and eye-catching finish to impress the US market.
The IBF, WBA and WBO champion will travel to Florida this week to conduct the late stages of his training camp, before moving on to New York aiming to extend his perfect 21-fight record.
“Sometimes I’m sparring now and yesterday I was tired so I thought I’d work on not getting hit,” added Joshua.
Joshua’s trainer Rob McCracken has insisted on the team using their own unit to train in the US rather than using an existing gym in order to avoid distraction and maintain routine.
He says Joshua’s US debut is “as big as it gets” for the Briton and echoes improvements in the champion’s approach to the sport.