The muscles that move your eyes are the most active muscles in your body.
Why it is true
These muscles perform over one hundred thousand coordinated movements per day to allow focusing, tracking objects, and maintaining visual balance, surpassing any other muscle group in frequency of use.
Source: Ophthalmology
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.