After finishing the marathon, he was completely exhausted.
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grammar
精疲力尽 is a four-character idiom (成语) structured as two parallel pairs: 精疲 (spirit tired) + 力尽 (strength exhausted). It's used as a predicate or complement, often after 累得 (so tired that) or with 已经 (already).
usage
Close synonyms: 筋疲力尽 (same meaning, uses 筋 'muscles' instead of 精 'spirit'), 疲惫不堪 (exhausted beyond endurance). 精疲力尽 is the most common of these in everyday speech.
