When you flex, what makes your muscles get big and hard?

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Offline CockOnLock

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I know they're expanding but, are they becoming filled with something?
What's going on in there to make that chance from squishy to hard muscle?

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Offline cheryl j

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Re: When you flex, what makes your muscles get big and hard?
« Reply #1 on: 08/06/2012 02:31:54 »
They aren't really expanding or filling with anything - more like "bunching up." When muscles contract, they shorten in length, and therefore become thicker or denser. They shorten when microscopic protein filaments called actin and myosin inside muscle cells slide past one another shortening the gaps between one of them. It's easier to understand if you look at a diagram. Google muscle contraction or actin and myosin or sliding filament theory.