lithe

adaptable, ductile, elastic, fluid, kneadable, malleable, modifiable, plastic, variable, yielding

droopy, flaccid, floppy, limp

semiflexible

acrobatic, flexible, limber, loose-jointed, pliable, pliant, supple

adroit, deft, dexterous (also dextrous), light-fingered

fleet-footed, sure-footed

athletic, balletic, coordinated

clean-limbed, trim

sylphlike, willowy

angular, rawboned, scraggy, scrawny, sinewy, wiry

lank, lanky, rangy, reedy, spindling, spindly, stringy, twiggy, waspish, weedy

anorexic, cadaverous, emaciated, gaunt, haggard, pinched, skeletal, wasted, wizened

meager (or meagre), puny, slight