The former England international turns 32 at the start of next year, and says that the threat of being replaced by younger stars has ensured he stays motivated to perform to the best of his ability.
"I know it sounds stupid to some people but I never feel like I have cemented my place, that it can all be taken away from me very quickly," he told the club's official website.
"I always try to do something different each summer to try to get that extra couple of percent. I went boxing, I've always eaten well and now I eat to the absolute maximum.
"We are all getting older, but another way of looking at it is Daniel Agger and Martin Skrtel are getting more experienced which is going to help them.
"They are coming into the prime of their careers. I am not stupid. I am 32 in January. It will happen one day."
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