After returning to the England squad under the new leadership of coach Brendon McCullum and captain Ben Stokes, he helped the team win six of their seven tests this summer by taking 29 wickets.
Earlier this week, McCullum said Broad will be part of the England squad for next year's Ashes, along with James Anderson (40).
"I am always someone who has needed new challenges and I've always maintained that if I'm not working on something ... my training becomes stale, and I become stale as a competitive sports person," Broad wrote in his Mail On Sunday column.
"It has left me excited about the rest of my England career. And that doesn't mean looking ahead to next year's Ashes. We've made that mistake before.(McCullum) actually has a saying 'let's play where your feet are,' and that's been such a strength of ours all summer.
"We've stayed in the moment. So all I am thinking about is entering the next test match I play, the fittest I've ever been. At 36, that's quite a big thing to say."
England will play a three-match test series against Pakistan in Rawalpindi, Multan and Karachi in December, following the Twenty20 World Cup in Australia.
