Gavin Rees, who faces Derry Mathews on Saturday, says there will be no repeat of the alarming burn-out that almost cost him victory in his previous fight.
Welshman Rees beat Andrew Murray in June to claim the vacant European title, but after being in control early on he tired badly in the latter stages.
But the 31-year-old insists that a new training discipline will ensure he can easily go the distance against Mathews.
"I'm on a different diet and I'm a completely different fighter," he said.
"I did 12 rounds sparring last week easy. I just need to take that into the fight."
According to Rees, the fitness problem against Murray was a result of losing a stone in weight too quickly to make the 135lb limit.
"It killed my legs, the fitness just wasn't there in the fight," he said.
"This time the weight's much better and I've only got four pounds to lose in five days. It's hard to believe.
"I've got a good nutritionist and everything has gone perfect."
Rees hopes Saturday's fight with Mathews in Newport is a step towards securing a world title shot next year.
The former WBA light-welterweight champion is the clear favourite, but he says no unnecessary risks will be taken against a fighter who has won four times in 2011 since coming out of retirement.
"People say it's a formality and I'm hot favourite with the bookies, but he's a good opponent," Rees said.
"He's had a couple of good wins lately but if it goes past six rounds I want to show everybody I don't get tired after six rounds - that was just a weight issue.
"I want to look good in winning."