Origin and history of upswing

Old English swinge "a stroke, blow with a weapon; chastisement," from the verb (see swing (v.)). Some later senses developed directly from the modern verb.

 By late 15c. generally as "an act or motion of swinging, the sweep of a body moving in suspension" (used with much latitude). The meaning "suspended seat on ropes fastened to points of support" is from 1680s. The sense of "free-swinging movement or gait" is by 1730. The meaning "shift of public opinion" is from 1899.

 The meaning "variety of big dance-band music with a swinging rhythm" based on the performer's lag or rush of the time, is attested by 1933, though the sense has been traced back to 1888. An all-but-ineffable quality yet what wants it don't mean a thing; its heyday was mid-1930s to mid-1940s.

Phrase in full swing "in total effect or operation" (1560s) perhaps is from bell-ringing. The backyard or playground swing-set "one or more children's swings on a rigid frame" is by 1912, American English.

a prefix bringing various senses of up, including "toward a more elevated position; at or to a source, head, or center; in or to an erect position;" originally from Old English up (adv.). It corresponds to Dutch op-, German auf-, Old Norse upp-.

Modern formations with it include upchuck, update, upfield, upgrade (v.), upload, upswing (n.), upscale, uptight, all from 20c.

The prefix was highly productive in Old and Middle English (and among poets of all eras), forming up-verbs where modern English uses "verb up." Some of these (uplift) survive.

Many do not: Upbear, upblaze, upblow, upbreak, updress, upgive, uphang, upshut, upsit, upspeak, uptie, upthrow, upwake, etc. The old verbs are not so much archaic as dissolved. In a few cases two forms survive to sustain (sometimes contrary) distinct senses: Hold up and uphold; set up and upset.