“It wasn’t an easy decision,” said the 33-year-old central defender. “The fact of the matter is my body can’t do what I want it to anymore.
“That’s something you get used to as you get older and you learn to read the game differently, but what I found at points of this season was my body couldn’t do what I needed it to and that’s a completely different thing.
Having linked up with Aidy Boothroyd for a second time, Carlisle played a key role as the Cobblers came so close to winning promotion.
“I have thoroughly enjoyed my entire career, but even moreso this season," he added.
"At my age and my time of life, to be able to contribute to this squad and such a special thing that happened here with Aidy taking a group of ragamuffins and almost non-league players last year all the way to Wembley.”
Source: Cobblers Mad