Long, flat pieces of wood, usually thick boards; also means core exercises that require holding a rigid body position.
From Old French 'planke' (wooden board), derived from Latin 'planca' (board). The word has meant wooden boards since the 1200s; the fitness meaning is modern, emerging in the 1990s-2000s.
The 'plank' exercise became wildly popular in fitness because it works your entire core in one movement, but Vikings and ancient builders were using actual wooden planks long before it became a fitness trend!
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