The earliest recorded English sense of nervous is sinewy or strong. Latin nervōsus described tendons, toughness and vigor; English borrowed through both Latin and Anglo-French.
Latin and French intermediate forms are omitted. Bodily and emotional meanings continue to overlap.
Source
Merriam-Webster: nervousArchaic sense 5 and the first-use record establish sinewy/strong as earliest; Word History gives the Latin glosses and dual borrowing route.