1630s (athletical is from 1590s), "pertaining to an athlete or to contests of physical strength," from Latin athleticus, from Greek athletikos, from athletes "contestant in the games" (see athlete). Meaning "strong of body; vigorous; lusty; robust" [Johnson, who spells it athletick] is from 1650s.
in the names of sciences or disciplines (acoustics, aerobics, economics, etc.), a 16c. revival of the classical custom of using the neuter plural of adjectives with Greek -ikos "pertaining to" (see -ic) to mean "matters relevant to" and also as the titles of treatises about them. Subject matters that acquired their English names before c. 1500, however, tend to be singular in form (arithmetic, logic, magic, music, rhetoric). The grammatical number of words in -ics (mathematics is/mathematics are) is a confused question.
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Harper, D. (n.d.). Etymology of athletics. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/athletics