The antonyms of "stiff-backed" include a wide range of words describing posture and movement. These antonyms include flexible, supple, relaxed, limber, loose-limbed, bendy, pliable, fluid, and nimble. These words describe bodies that are limber, lithe, and well-loosened. Individuals with these opposing traits have the ability to bend, twist, and contort their bodies with ease. Their movements are smooth, fluid, and effortless. In contrast, individuals with stiff-backed traits tend to move in a rigid, inflexible, and robotic manner. These antonyms highlight the importance of physical flexibility and adaptability for optimal health and wellness.