It’s quite common to read of people – particularly sportsmen and performers – promising to “give 110%” effort. England cricketer Andrew Flintoff, for example, once promised to give “110% in every game” he played. Of course, to do so would be impossible. When something is finite, 100% means all of it. You can’t give more effort than you can give. The term only really makes sense when comparing two amounts. You could put 110% effort into one game as compared to that of a previous game, but only if you hadn’t tried properly in the previous game, or if (say) you’re fitter and can now make more of an effort. Still, you can’t put in more than 100% of your available effort.
Of course, it could be argued that this term is an acceptable colloquialism. Flintoff just meant he would try his absolute hardest. As so often, whether you should use the phrase depends on what you are writing. The term sometimes crops up in serious, factual pieces such as job advertisements or job applications, where it is surely inappropriate. If you were creating a fictional character with very precise language, you wouldn’t expect them to use such a term. But if you were creating a sporting character it may well be entirely reasonable for them to say something like this.
One problem, though, is the inflation that sets in once the 100% barrier has been breached. If it’s possible to give 110%, is giving 120% trying even harder? Obviously neither claim makes logical sense; the language just becomes more and more meaningless. It’s fairly common for people to say they will give 200%, or 1000% effort. Phil Brown, the manager of an English football club, recently claimed his players were “one million percent” behind him. Search the internet and you can find people saying they will give one billion percent effort. And so on, presumably, until we reach infinity percent.
Terms like “giving 110% effort” are now clichés. If you want to convey the idea of trying really hard, it’s better to find another way of expressing the idea.