Is it farther or further?
1680s, "pertaining to muscles," from Latin musculus (see muscle (n.)) + -ar. Earlier in same sense was musculous (early 15c.). Meaning "having well-developed muscles" is from 1736. Muscular Christianity (1857) is originally in reference to philosophy of Anglican clergyman and novelist Charles Kingsley (1819-1875). Muscular dystrophy attested from 1886.
muscular mus·cu·lar (mŭs'kyə-lər)
Of, relating to, or consisting of muscle.
Having or characterized by well-developed muscles.