Kevin Pietersen has said that back-to-back Ashes series have left England "a bit fragile".
The tourists had looked to be in a strong position after leading by 91 at the end of first innings in the fourth Test in Melbourne, but a batting collapse allowed Australia to take control again.
The batsman told Sky Sports News: "Scoring's been incredibly tough. It's been a series of hard work. I think people mustn't forget as well, it's never been done before, that guys have got to go and endure 10 back-to-back Ashes Test matches.
"I've been told a number of post-Olympic athletes go into some sort of depression or negative frame of mind. I'm not saying we are in some sort of depression or negative frame of mind, but after you've competed at such a level, post that competition, mentally you are a bit fragile.
"To play an Ashes and then another Ashes, and for us being away from home, it's a tough gig. It's been an incredibly pressurised situation. Playing back-to-back Ashes series and being away for the second leg and not starting in the manner we are accustomed to has been incredibly difficult."
Australia will resume on 30-0 on day four, needing a total of 231 runs to win the fourth Test.
