The MRC scale for muscle power was first published in 1943 in a document called 'Aids to the Investigation of Peripheral Nerve Injuries (War Memorandum No. 7)'. This became a standard text resource which was reprinted many times, and is referred to widely in a number of documents/papers. In the 1970s the document was republished with the title 'Aids to the Examination of the Peripheral Nervous System (Memorandum No. 45)'.
The muscle scale grades muscle power on a scale of 0 to 5 in relation to the maximum expected for that muscle. In a recent comparison to an analogue scale the MRC scale is more reliable and accurate for clinical assessment in weak muscles (grades 0-3) while an analogue scale is more reliable and accurate for the assessment of stronger muscles (grades 4 and 5).