Having fallen to loss inside two days in the first Test in Perth, the visitors had five training sessions before the second Test but opted against a pink ball practice match.
England were beaten by eight wicket in four days at the Gabba and McCullum says the training methods backfired.
“Leading into this Test match, I actually felt like we over-prepared, to be honest,” the England mentor told Australian broadcaster Channel 7.
“We had five intense training days. When you’re in the heat of the battle, as we all know, sometimes the most important thing is to feel a little bit fresh and make sure your top two inches (of your head) is completely sound.
“I think the boys just need a few days off, and probably need to just change up a few of the training methods a little bit.
“I’m a horse-racing man, and you wouldn’t just keep doing the same thing with your horse, you’d send it around in figure-eights or over the little jumps, just to try and switch it on a bit. We’ll look at some alternative methods over the next few days.”
The tourists have planned a trip to the resort town of Noosa before travelling to Adelaide, where the third Test of the series will start on 17 December.
England captain Ben Stokes defended the Noosa trip, saying it was important for his players to stay fresh in an intense series.
“This is a high-pressure environment. We chose to do this. We’re lucky enough to do this,” Stokes said.
“It comes with the job, but it’s also very, very important that when you do get the opportunity that you are able to go away and refresh your mind because obviously in (Adelaide) we need to be not only physically good, but mentally very good as well.”
