The idiom "筋疲力尽" (jīn pí lì jìn) is formed through a parallel and symmetrical four-character structure common in classical Chinese, where "筋" (muscles/tendons) and "力" (strength) are paired nouns, and "疲" (weary) and "尽" (exhausted) are paired verbs/adjectives describing their state. The compound thus creates a vivid, compounded meaning through two parallel phrases—"筋疲" (muscles weary) and "力尽" (strength spent)—that together emphasize a state of total physical and mental exhaustion, with the repetition amplifying the sense of complete depletion.