Joseph Parker admits he watches Anthony Joshua's "new training" techniques and cannot understand why his rival champion "tires" in fights.
The New Zealander has been preparing in Las Vegas for the unification clash against Joshua, with three world heavyweight titles on the line at the Principality Stadium in Cardiff on March 31.
Joshua returned to his normal base at Sheffield's English Institute of Sport and this week posted a picture of his muscle-bound physique, but Parker has questioned why his opponent is still showing stamina issues after undergoing the newest forms of strength and conditioning.
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"My body type, even though it's not really muscular, [has] worked for us," Parker told Sky Sports. "We know that we can fight hard from round one to round 12. It's all that matters."
Asked about Joshua's preparations, he added: "When you watch him, when you see all the training, it's like they are doing all this new training and it looks really hard, and it looks intense, and it looks the type of training that will prepare you for 12 rounds.
"But, in saying that, just maybe their team need to work on a few things. We know that our team has a good structure and a good training programme that will allow us to fight 12 rounds, if we need it.
"But I'm not sure why he tires, that's something he has to sort of figure out."
Parker has proven his fitness by going the full 12 rounds in four of his last six fights and trainer Kevin Barry has suggested that Joshua could be forced to withstand a determined late assault.
"I see videos posted everywhere of him doing the most sophisticated, new age training methods that man has ever seen and, yet he's looked very tired in his last couple of fights," said Barry.
"Every time he's been asked to go on to the later rounds, he's really struggled so that's a question for his training staff.
"He wouldn't want to be slowing against Joe, because I can promise you this. Joe will be coming on in the later rounds."