Wiktionary
n. 1 (context idiomatic US sports informal English) A level of effort exceeding one's sustained capacity, possibly risking injury. 2 (context idiomatic colloquial English) The exertion of more than seems possible, hence 110%, not 100%, the usual maximum amount possible.
Usage examples of "a hundred and ten percent".
She won't make the shield a hundred and ten percent efficient, so that when the particle storm hits, nothing at all gets through to Earth.
But he had the feeling that the old days were coming back, just once more, as it had been working on Apollo, when everyone worked a hundred and ten percent and the color of your carpet didn't matter so much as what you knew and what you could do.
They all moved briskly, as if filled with energy and purpose, as if they were, to a man, reluctant to give their employers less than a hundred and ten percent in return for their salaries.