Objective[edit | edit source]
The Oxford Muscle Scale is a numerical rating scale used to quantify the power or strength produced by the contraction of a muscle. The scale was originally developed by a UK government research group called the Medical Research Council (MRC), and first described in a paper titled Aids to the Investigation of Peripheral Nerve Injuries (War Memorandum No. 7), released in 1943 and reprinted as an updated version in 1976. Measurement is scored on a 0 to 5 scale, with 5 representing maximal strength.
The Medical Research Council Sum-Score (MRC-SS), a derivative of the Oxford Muscle Scale, was developed in the late 1980s and first described by Kleyweg, Van Der Meché, and Schmitz (1991) as a tool for assessing and tracking general muscle strength in individuals with Guillian-Barré syndrome. Currently though, the MRC-SS is a tool commonly used to determine and track the development of Intensive Care Unit (ICU) Acquired Weakness.
Intended Population[edit | edit source]
This measure was originally developed for use in patients diagnosed with Guillian-Barré syndrome, including those who were considered bed bound or were receiving mechanical ventilation. Given the characteristics of this originally intended population, the MRC-SS is now more commonly used in the general critical care and ICU populations, with a specific emphasis on its use as a method for identifying and tracking ICU Acquired Weakness.
Method of Use[edit | edit source]
Assessment of the MRC-SS can be completed in a patient's hospital room through the systematic testing of strength, bilaterally, for six muscle groups to produce a score out of 60. If the total score achieved is below 48/60, this is considered an indication of the presence of ICU Acquired Weakness. Of note, it is crucial that the patient possess a degree of cognitive alertness that allows participation in testing. If the patient is unable to follow basic directions, MRC-SS is likely not appropriate.
|Muscle Groups Tested|
|Muscle Grading Scores |
|0||No detectable muscle contraction (visible or palpation)|
|1||Detectable contraction (visible or palpation), but no movement achieved|
|2||Limb movement achieved, but unable to move against gravity|
|3||Limb movement against resistance of gravity|
|4||Limb movement against gravity and external resistance|
Evidence[edit | edit source]
While the MRC-SS was originally described by Kleyweg et al. in 1991, more recent studies have examined aspects of this tool as they relate to critically ill patients and the detection of ICU Acquired Weakness. 
Reliability[edit | edit source]
Intraclass Correlational Coefficient (ICC) = 0.95 (0.92-0.97)
- Significant weakness (MRC-SS <48) = 0.68
- Severe Weakness (MRC-SS <36) = 0.93
Validity[edit | edit source]
No data available regarding validity of the MRC-SS.
Responsiveness[edit | edit source]
No data available regarding the responsiveness of the MRC-SS.
Miscellaneous[edit | edit source]
Ceiling Effect: The MRC-SS has been noted to have a ceiling effect due to the vagueness of the demarcation between the scores of 4/5 and 5/5. Discrimination of the two scores as either normal (5/5) or movement against resistance (4/5) allows for a degree of subjectivity that can produce variability among patients whose scores fall withing these ratings.
Predictive Value: An MRC-SS score <48 has been found to have some association with the length of both ICU and hospital stays for patient. When MRC-SS is assessed when the patient first awakens after surgery, sensitivity and specificity associated with specific outcomes were as follows:
- ICU Length of Stay (≤14 days and >14 days): Sensitivity 92.9%, Specificity 40.5%
- Hospital Length of Stay (≤28 days and >28 days): Sensitivity 84.2%, Specificity 40.7%
Resources[edit | edit source]
References[edit | edit source]
- UK Research and Innovation. MRC Muscle Scale. Available from: https://www.ukri.org/councils/mrc/facilities-and-resources/find-an-mrc-facility-or-resource/mrc-muscle-scale/ (accessed 27 Jan 2023).
- Kleyweg RP, Van Der Meché FG, Schmitz PI. Interobserver agreement in the assessment of muscle strength and functional abilities in Guillain-Barré syndrome. Muscle & Nerve 1991; 14(11): 1103-1109
- Connolly B, Thompson A, Moxham J, Hart N. Relationship Of Medical Research Council Sum-Score With Physical Function In Patients Post Critical Illness. American Journal of Respiratory and Critical Care Medicine 2012;185:A3075.
- Hermans G, Van den Berghe. Clinical Review: intensive care unit acquired weakness. Critical Care 2015; 19(274): n.p.
- Hermans G, Clerckx B, Vanhullebusch T, Segers J, Vanpee G, Robbeets C, et al. Interobserver agreement of medical research council sum-score and handgrip strength in the intensive care unit. Muscle and Nerve 2012; 45(1): 18-25.
- Connolly BA, Jones GD, Curtis AA, Murphy PB, Douiri A, Hopkinson NS, et al. Clinical predictive value of manual muscle strength testing during critical illness: an observational cohort study. Crit Care. 2013; 17(5): R229.