Rigamortis by definition is when the muscles of the body become stiff due to the build up of lactic acid in the muscles. the amount of lactic acid and how fast a body goes into this state depends on how much the rat was moving around working out the muscles. The average is 3-6 hours after death and usually goes away after about 36 hours. If you are using rats that have been frozen for at least a month then you will never see any signs of rigamortis. Except when they are still frozen.

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