The Irishman's fitness was crucial in Sunderland's survival battle.
He said: "Thankfully the fitness has been very good this year, that's been the main thing.
"You are maintaining everything off the pitch in terms of the work you do in the gym and the core work - especially when you are getting into your 30s rather than your 20s, it's definitely needed more.
"But also you know you are preparing yourself right and you can cope with it.
"Thankfully, I have never had the major injuries that can hold you back towards the latter end of your career. I feel very fresh."