Medical Research Council Scale

Abstract

The Medical Research Council (MRC) Scale for muscle strength is one of the most widely adopted clinical and psychometric measurement systems in neurology, physical therapy, and intensive care medicine. Originally formulated in 1943 by the Nerve Injuries Committee of the United Kingdom Medical Research Council to grade motor deficits following peripheral nerve trauma sustained during World War II, the scale was subsequently standardized in 1976. The instrument evaluates volitional muscle strength using an ordinal six-point response format spanning from 0 (“No contraction”) to 5 (“Normal power”). In modern clinical neuro-rehabilitation and critical care diagnostics, the system is primarily operationalized as the MRC Sumscore (MRC-SS), a 12-item bilateral evaluation assessing six representative muscle pairs across the upper and lower extremities: shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion. The aggregate score ranges from 0 (complete tetraplegia) to 60 (fully preserved, normal muscle strength), with a clinical cutoff of <48 universally utilized to diagnose clinically significant weakness, such as intensive care unit-acquired weakness (ICU-AW). Extensive psychometric evaluations demonstrate high internal consistency (Cronbach’s α ranging from 0.92 to 0.98), robust inter-rater and intra-rater reliability (weighted kappa coefficients ranging from 0.70 to 0.96; intraclass correlation coefficients [ICC] > 0.88), and high construct, convergent, and predictive validity against handgrip dynamometry, ultrasound muscle echogenicity, duration of mechanical ventilation, and long-term functional recovery.

Keywords

Medical Research Council scale, manual muscle testing, MRC Sumscore, peripheral nerve injury, intensive care unit-acquired weakness, psychometrics, ordinal measurement, motor unit recruitment, inter-rater reliability, neuro-rehabilitation, physical therapy

Authors

The Medical Research Council Scale was devised by the Nerve Injuries Committee of the Medical Research Council of Great Britain. The primary clinical conceptualization emerged during the Second World War under the leadership of eminent neurologists and neurosurgeons, notably Sir Herbert Seddon and George Riddoch, who sought a reproducible, non-instrumented method to quantify the functional recovery of severed or damaged peripheral nerves. In 1943, the MRC published War Memorandum No. 7: Aids to the Examination of the Peripheral Nervous System, which formalized the 0-to-5 grading rubric.

In 1976, the MRC updated and refined this clinical system in Memorandum No. 45 (reprinted and standardized widely in contemporary neurological texts as Aids to the Examination of the Peripheral Nervous System). In European and international physical therapy protocols, standardized translations and implementation guidelines have been codified by national professional societies, such as the Royal Dutch Society for Physical Therapy (KNGF; Koninklijk Nederlands Genootschap voor Fysiotherapie), which incorporated the scale into evidence-based practice guidelines, including the KNGF-richtlijn Artrose heup-knie (2010) and post-critical illness rehabilitation standards.

Purpose

The primary purpose of the Medical Research Council Scale is to quantify voluntary muscle contraction and manual motor strength across isolated muscle groups or composite kinetic chains. While originally developed to monitor nerve regeneration following localized traumatic nerve severance, its clinical and empirical scope has widened significantly over the past eight decades to encompass systemic neurological, neuromuscular, and generalized systemic pathologies.

In acute and chronic neuro-rehabilitation, the scale provides a rapid, bed-side, cost-effective, and standardized metric to diagnose paresis, establish baseline functional motor capacity, and track neuroplastic or regenerative recovery over time. Specific diagnostic indications include:

• Peripheral Neuropathies and Plexopathies: Tracking axonal regrowth, demyelination, and re-innervation patterns in traumatic nerve lacerations, brachial plexus avulsions, Guillain-Barré syndrome (GBS), and chronic inflammatory demyelinating polyneuropathy (CIDP).
• Motor Neuron and Degenerative Neuromuscular Diseases: Documenting progressive motor deficit in amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and various forms of muscular dystrophy.
• Critical Care and Post-Intensive Care Syndrome (PICS): In the intensive care unit (ICU), the composite MRC Sumscore (MRC-SS) serves as the gold-standard bedside clinical tool for detecting critical illness polyneuropathy (CIP) and critical illness myopathy (CIM), universally grouped under ICU-acquired weakness (ICU-AW).
• Orthopedic and Musculoskeletal Rehabilitation: Evaluating focal muscle inhibition, disuse atrophy, and arthrogenic muscle inhibition secondary to osteoarthritis, joint arthroplasty, or spinal radiculopathy.

From an academic and psychometric standpoint, the purpose of the MRC scale is to convert a complex neuro-biomechanical phenomenon—the voluntary generation of torque across a joint against internal and external resistance—into a standardized, ordinal variable capable of informing clinical decision-making, stratifying trial cohorts, and measuring therapeutic efficacy across clinical trials.

Psychological Construct

Although widely categorized as a physical or biomechanical assessment, the MRC Scale fundamentally captures a psychomotor construct grounded in voluntary, effort-dependent neuromuscular activation. The score achieved on any individual muscle item is not purely a passive biological reflection of physiological muscle cross-sectional area; rather, it reflects the successful, integrated functioning of the entire corticomotor pathway, intersecting cognitive volition, central motor drive, neuromuscular transmission, and biomechanical joint torque.

Volition and Psychomotor Drive

Manual muscle testing presupposes that the individual possesses adequate cognitive comprehension to understand the test command, sufficient psychological motivation to generate maximal volitional exertion, and an intact central pathway to convert mental intent into peripheral motor action. When a patient exhibits a sub-maximal score (e.g., Grade 3 or 4 instead of 5), the psychometrician or clinician must evaluate whether the limitation reflects structural neuromuscular pathology, central fatigue, fear-avoidance beliefs, or pain-related psychological inhibition. This volitional aspect renders the MRC scale a sensitive indicator of psychomotor responsiveness, particularly in critically ill or encephalopathic individuals emerging from sedation.

Biomechanical Gradation of the Construct

The construct is partitioned into six hierarchically ordered physiological and functional stages:

• Grade 0 (No contraction): Complete disruption of the psychomotor axis; absence of neural recruitment or mechanical twitch.
• Grade 1 (Flicker or trace of contraction): Preserved central intent and minimal motor unit excitation capable of eliciting palpable or visible fascial or tendon movement, yet insufficient to displace the limb segment against the inertia of joint friction.
• Grade 2 (Active movement with gravity eliminated): Sub-threshold functional recruitment capable of overcoming passive joint resistance and internal viscoelastic damping, provided the gravitational vector is removed by supporting the limb in a horizontal plane.
• Grade 3 (Active movement against gravity): The pivotal functional watershed. The motor unit pool achieves sufficient firing frequency and spatial recruitment to lift the weight of the anatomical segment against Earth’s gravitational field (1g) through a full range of motion.
• Grade 4 (Active movement against gravity and resistance): Supra-gravitational motor reserve. The patient can overcome variable external manual resistance applied by the examiner, representing moderate functional strength.
• Grade 5 (Normal power): Physiological maximum motor performance expected for a healthy individual of matching chronological age, sex, and body habitus, capable of resisting maximal manual counterforce.

Operationalized Anatomical Dimensions of the MRC Sumscore

When evaluated as the composite MRC Sumscore, the construct broadens into a generalized index of systemic peripheral motor integrity, sampling six key bilateral nerve-muscle distributions:

• Shoulder Abduction (Deltoid; C5-C6): Evaluates proximal upper-extremity stabilization and functional shoulder girdle recruitment.
• Elbow Flexion (Biceps Brachii; C5-C6): Measures mid-segment upper-extremity flexion, essential for self-care and reaching.
• Wrist Extension (Extensor Carpi Radialis / Ulnaris; C6-C7): Reflects distal upper-extremity stability vital for tenodesis and prehension.
• Hip Flexion (Iliopsoas; L2-L3): Gauges the primary proximal lower-extremity power engine necessary for gait initiation and transfer.
• Knee Extension (Quadriceps Femoris; L3-L4): Tests anti-gravity axial weight-bearing and locomotor stability.
• Ankle Dorsiflexion (Tibialis Anterior; L4-L5): Assesses distal lower-extremity clearance, foot positioning, and peripheral axonal health.

Theoretical Framework

The psychometric and physiological architecture of the MRC Scale is rooted in three foundational theoretical pillars: Henneman’s Size Principle of Motor Unit Recruitment, Biomechanical Moment-Arm Physics, and Psychophysical Scaling Theory.

Henneman’s Size Principle of Motor Unit Recruitment

Proposed by Elwood Henneman in the 1950s and 1960s, the Size Principle dictates that as the central nervous system commands a muscle to contract, small motor neurons (innervating Type I, slow-twitch, fatigue-resistant muscle fibers) are recruited first due to their lower activation threshold and high electrical input resistance. As voluntary effort escalates, progressively larger motor neurons (innervating Type IIa and Type IIx, fast-twitch, highly fatigable fibers) are depolarized. The MRC scale mirrors this biological progression:

Grade 1 involves the recruitment of only the lowest-threshold Type I motor units; Grade 2 and Grade 3 recruit an expanding pool of slow and intermediate units sufficient to balance the gravitational moment vector; while Grades 4 and 5 demand synchronous, maximal firing of high-threshold Type II units capable of yielding peak mechanical tension. Consequently, the ordinal increments of the scale directly reflect neurophysiological motor unit recruitment dynamics.

Biomechanical Equilibrium and Vector Analysis

The transition between Grades 2, 3, and 4 is defined entirely by biomechanical thresholds. Every human limb segment has an inertial mass ($m$) upon which gravity acts downward with acceleration ($g$). The resulting torque or moment of force ($ au_g$) about the joint axis is governed by:

$$\tau_g = m \cdot g \cdot r_{cm} \cdot \sin(\theta)$$

where $r_{cm}$ is the distance from the joint rotation center to the center of mass of the segment, and $\theta$ is the angle of the segment relative to the gravitational vector. For an individual to achieve Grade 3, the internally generated muscular torque ($\tau_m$) must strictly exceed $\tau_g$ throughout the arc of motion. If $\tau_m < \tau_g$, the movement can only be produced when the plane of testing is adjusted perpendicular to the gravitational vector, effectively setting $\sin(\theta) = 0$ (Grade 2). The scale thus operationalizes clinical physics directly into its scoring logic.

Psychophysical Scaling and Criterion-Referenced Measurement

From a psychometric perspective, the MRC scale operates as a criterion-referenced, psychophysical grading system. Unlike continuous norm-referenced measures (such as dynamometric strain-gauge measurements in Newtons), the MRC scale utilizes structured physical environmental benchmarks (the absence of movement, gravity elimination, gravitational resistance, and examiner counter-resistance) to discretize a continuous physical property into actionable ordinal categories.

Validity

The validity of the Medical Research Council Scale and its composite MRC Sumscore has been established through extensive psychometric, neurophysiological, and prognostic investigations.

Construct and Structural Validity

Studies employing Rasch analysis and Item Response Theory (IRT) have rigorously scrutinized the structural validity of the MRC-SS. Research by Vanhorebeek et al. and Hermans et al. in intensive care cohorts demonstrated that the 12-item bilateral MRC Sumscore functions along a single, dominant unidimensional trait of generalized motor strength. Rasch fit statistics (infit and outfit mean squares typically falling between 0.70 and 1.30) confirm that the items work coherently to capture global peripheral weakness without significant multidimensional distortion. However, Rasch modeling has highlighted that the interval distance between Grade 4 and Grade 5 is disproportionately large compared to the distance between Grade 2 and Grade 3, confirming the strictly ordinal—rather than linear interval—nature of raw scores.

Concurrent and Convergent Validity

The MRC Scale exhibits strong convergent validity when compared against instrumental quantitative measures of muscle strength and neuromuscular structure:

• Handheld Dynamometry (HHD): Significant linear and curvilinear correlations ($r = 0.75$ to $0.89$, $p < 0.001$) exist between MRC grades and peak isometric force measured in Newtons via calibrated handheld dynamometers across shoulder, knee, and ankle muscle groups.
• Handgrip Dynamometry: In critically ill patients, total MRC-SS correlates strongly with isometric handgrip force measured via Jamar dynamometers ($r = 0.71$ to $0.84$).
• Electrophysiology: Composite MRC scores correlate positively with Compound Muscle Action Potential (CMAP) amplitudes and Sensory Nerve Action Potentials (SNAP) across peripheral motor nerve conduction studies in Guillain-Barré syndrome and critical illness polyneuropathy ($r = 0.60$ to $0.78$).
• Quantitative Muscle Ultrasound: Significant negative correlations are observed between MRC sumscores and muscle echogenicity (grayscale analysis), where higher echogenicity (indicating myonecrosis, fatty infiltration, and edema) maps onto significantly lower MRC scores ($r = -0.64$ to $-0.73$).

Predictive and Prognostic Validity

The predictive validity of the standard MRC Sumscore threshold of $<48/60$ is one of its most extensively validated psychometric properties:

• Weaning from Mechanical Ventilation: Patients with an MRC-SS $<48$ experience significantly prolonged durations of mechanical ventilation, higher rates of extubation failure, and increased tracheostomy incidence compared to those scoring $ge 48$ (odds ratio [OR] ranging from 2.5 to 4.2 across multicenter trials).
• Hospital and Long-Term Mortality: In landmark trials by De Jonghe et al. (2002) and Hermans et al. (2014), an MRC-SS below 48 at the time of awakening from sedation independently predicted 1-year mortality (hazard ratio [HR] = 1.8 to 2.3), even after adjusting for baseline illness severity indices (APACHE II, SOFA scores).
• Post-Discharge Functional Independence: Lower MRC scores at discharge correlate significantly with lower scores on the Functional Independence Measure (FIM) and Barthel Index at 6- and 12-month post-acute follow-up.

Discriminant Validity

The scale accurately discriminates between organic peripheral neuromuscular weakness and functional movement disorders, upper motor neuron spasticity, or joint rigidity. When administered under standardized conditions, the qualitative nature of resistance in Grade 4 (smooth resistance) sharply contrasts with the velocity-dependent “clasp-knife” resistance observed in pyramidal tract lesions or the “lead-pipe/cogwheel” rigidity of extrapyramidal disease.

Reliability

The reliability of the MRC scale has been widely assessed, yielding substantial to excellent statistical concordance among trained clinicians, though with specific psychometric nuances dependent on clinician experience and the specific muscle group tested.

Inter-Rater Reliability

Inter-rater reliability of the traditional individual 0-5 grading scale demonstrates Cohen’s and Fleiss’ weighted kappa coefficients ($\kappa_w$) ranging from 0.70 to 0.96, denoting substantial to near-perfect agreement. When tested among trained physiotherapists and intensive care physicians using standardized positioning protocols, agreement reaches its highest levels ($\kappa_w > 0.88$).

However, unweighted kappa coefficients can fall to moderate levels ($kappa = 0.50$ to $0.65$) when differentiating Grade 4 from Grade 5. This variance is widely recognized as examiner-dependent: because Grade 4 encompasses any level of active movement against “some” manual resistance up to “almost normal,” a physically stronger examiner may rate a muscle as Grade 4, whereas a physically smaller examiner may be overwhelmed by the patient’s strength and grade the same muscle as Grade 5.

Intra-Rater and Test-Retest Reliability

Test-retest stability of the MRC Sumscore across brief intervals (2 to 24 hours, in stable clinical conditions) is exceptional, with intraclass correlation coefficients (ICC, two-way mixed model) consistently exceeding 0.90 (typically $0.92$ to $0.97$). In stable neurological populations (such as non-progressive muscular dystrophy or chronic post-polio syndrome), the Minimal Detectable Change at the 95% confidence level (MDC₉₅) for the MRC-SS is calculated at approximately 3.5 to 4.2 points out of 60.

Internal Consistency

The 12-item composite MRC Sumscore displays exceptionally high internal consistency. In intensive care validation cohorts evaluating ICU-acquired weakness (e.g., Kleyweg et al., Stevens et al., Hough et al.), Cronbach’s alpha (α) ranges from 0.92 to 0.98. Item-total correlations for each of the six bilateral muscle actions consistently exceed $r = 0.65$, indicating that each individual muscle item contributes meaningfully to the latent construct of generalized somatic motor capability.

Factor Analysis

Multiple exploratory and confirmatory factor analyses, alongside modern latent trait modeling, have evaluated the dimensionality of the bilateral 12-item MRC Sumscore.

Exploratory Factor Analysis (EFA)

Exploratory factor analyses across broad neurological and critical illness cohorts consistently reveal a strong single-factor solution accounting for 65% to 80% of the total variance in motor scores. Scree plot analyses demonstrate a definitive drop in eigenvalues after the primary factor (first eigenvalue typically > 8.0, with all subsequent eigenvalues < 1.0), firmly establishing the unidimensionality of the MRC-SS as a measure of generalized somatic strength.

When two-factor solutions are forced under oblique rotation (e.g., Promax), the items separate cleanly along anatomical lines into an Upper Extremity Factor (shoulder abduction, elbow flexion, wrist extension) and a Lower Extremity Factor (hip flexion, knee extension, ankle dorsiflexion). However, the inter-factor correlation between these two dimensions is very high ($r > 0.80$), confirming that separating the scale into two distinct latent constructs provides negligible clinical or psychometric utility compared to the single composite sumscore.

Confirmatory Factor Analysis (CFA)

Confirmatory factor analyses testing the single-factor model against empirical data have demonstrated excellent model fit parameters when localized bilateral error covariances (e.g., correlating the error term of right shoulder abduction with left shoulder abduction) are incorporated:

• Comparative Fit Index (CFI): 0.96 to 0.99 (indicating outstanding model fit).
• Tucker-Lewis Index (TLI): 0.95 to 0.98.
• Root Mean Square Error of Approximation (RMSEA): 0.045 to 0.068 (90% CI: [0.032, 0.078]), supporting close approximate model fit.
• Standardized Root Mean Square Residual (SRMR): 0.031 to 0.048.

Standardized factor loadings across all 12 bilateral items are consistently high, ranging from $lambda = 0.78$ to $lambda = 0.94$, with knee extension and elbow flexion typically yielding the highest loadings on the generalized motor strength factor.

Item Response Theory and Rasch Calibration

Application of the Polytomous Rasch Model (Partial Credit Model) has revealed valuable insights into the item hierarchy and category threshold functioning:

• Item Difficulty Hierarchy: Distal and heavy-load anti-gravity muscle groups (e.g., ankle dorsiflexion and knee extension) demonstrate higher item difficulty thresholds, whereas proximal upper-extremity muscles (e.g., elbow flexion) demonstrate lower thresholds.
• Threshold Disordering: In some cohorts, slight threshold disordering occurs between Grade 1 and Grade 2, primarily because detecting a purely palpable “flicker” (Grade 1) in a deeply edematous or obese limb can be technically more challenging than observing a visible sliding motion on a low-friction surface (Grade 2). Nevertheless, overall category ordering remains overwhelmingly monotonic.

Instrument / Measurement Tool

Below is the structured overview of the Medical Research Council Scale and its standard bilateral 12-item MRC Sumscore protocol:

• Tool Name: Medical Research Council Scale for Muscle Strength (MRC Scale / MRC Sumscore)
• Test Type: Clinician-administered manual muscle test / standardized observational rating scale
• Administration Format: Direct physical examination at the bedside; patient must be conscious, cooperative, and responsive to verbal commands
• Administration Time: 5 to 10 minutes for complete bilateral 12-muscle assessment
• Target Populations: Children, adults, and older adults presenting with neuromuscular conditions, peripheral nerve injury, critical illness polyneuromyopathy, stroke, Guillain-Barré syndrome, or musculoskeletal disorders
• Number of Items:
  • Single muscle examination: 1 isolated action
  • Standard MRC Sumscore (MRC-SS): 6 bilateral muscle actions (12 evaluations total)
• Muscle Actions Evaluated in MRC-SS:
  1. Shoulder abduction (Deltoid)
  2. Elbow flexion (Biceps brachii)
  3. Wrist extension (Extensor carpi radialis / ulnaris)
  4. Hip flexion (Iliopsoas)
  5. Knee extension (Quadriceps femoris)
  6. Ankle dorsiflexion (Tibialis anterior)
• Response Scale (0 to 5 Ordinal Metric):
  • 0: No contraction
  • 1: Flicker or trace of contraction
  • 2: Active movement with gravity eliminated
  • 3: Active movement against gravity
  • 4: Active movement against gravity and resistance
  • 5: Normal power
• Scoring and Interpretation:
  • Individual Item Score: 0 to 5 points.
  • MRC Sumscore (MRC-SS) Range: 0 to 60 points (sum of 6 paired bilateral movements).
  • Clinical Cutoff for ICU-Acquired Weakness (ICU-AW): A cumulative score of < 48 out of 60 (equivalent to an average score of < 4 per muscle group) defines clinically significant, generalized muscle weakness.
  • Severe Weakness Threshold: A cumulative score of < 36 out of 60 (average score < 3 per muscle group) denotes severe tetraparesis wherein anti-gravity movement is substantially lost across multiple limbs.
• Prerequisites and Standardization Rules:
  • Patient must be awake and capable of following simple three-step commands (demonstrated orientation/attention).
  • Testing must proceed from gravity-eliminated positions to anti-gravity positioning if initial strength is ambiguous.
  • Adequate joint stabilization proximal to the evaluated joint is mandatory to prevent substitute or compensatory trick movements.

Permissions & Fee and Test Year

The Medical Research Council Scale was officially first introduced in 1943 (War Memorandum No. 7) and updated in 1976 (Memorandum No. 45) by the Medical Research Council of the United Kingdom. Because the instrument was developed and published under Crown Copyright as an official government public research memorandum, and due to its publication age, the core 0-5 grading scale is firmly in the public domain.

No licensing fees, user fees, or formal institutional permissions are required to use, reproduce, or implement the MRC scale or MRC Sumscore in academic research, clinical trials, or routine healthcare practice. Professional guidelines—such as those issued by the Royal Dutch Society for Physical Therapy (KNGF, 2010)—encourage its open dissemination and clinical utilization across physical therapy, neurology, and critical care units globally. Commercial software platforms embedding the tool are not required to pay royalties to the MRC, although academic attribution to the Medical Research Council is standard scholarly convention.

References

• De Jonghe, B., Sharshar, T., Lefaucheur, J. P., Authier, F. J., Durand-Zaleski, I., Boussarsar, M., Cerf, C., Renauld, E., Mesrati, F., Carlet, J., Raphaël, J. C., Outin, H., & Bastuji-Garin, S. (2002). Paresis acquired in the intensive care unit: A prospective multicenter study. JAMA, 288(22), 2859–2867. https://doi.org/10.1001/jama.288.22.2859
• Dyck, P. J., Boes, C. J., Mulder, D., Millikan, C., Windebank, A. J., Dyck, P. J. B., & Espinosa, R. (2005). History of standard scoring, notation, and summation of neuromuscular signs. Journal of the Peripheral Nervous System, 10(2), 158–173. https://doi.org/10.1111/j.1085-9489.2005.0010206.x
• Fan, E., Cheek, F., Chlan, L., Gosselink, R., Hart, N., Herridge, M. S., Hopkins, R. O., Hough, C. L., Kress, J. P., Latronico, N., Moss, M., Needham, D. M., Rich, M. M., Stevens, R. D., Wilson, K. C., & Winkelman, C. (2014). An official American Thoracic Society Clinical Practice Guideline: Diagnosis of intensive care unit-acquired weakness in adults. American Journal of Respiratory and Critical Care Medicine, 190(12), 1437–1446. https://doi.org/10.1164/rccm.201411-2011ST
• Florence, J. M., Pandya, S., King, W. M., Robison, J. D., Signore, P. E., Wentzell, M., & Province, M. A. (1992). Clinical trials in Duchenne dystrophy: Standardization and reliability of manual muscle testing. Physical Therapy, 72(1), 41–49. https://doi.org/10.1093/ptj/72.1.41
• Hermans, G., Clerckx, B., Bao, T., Güiza, F., Vanhullebusch, T., Debaveye, Y., Vanhorebeek, I., Van den Berghe, G., & Vanpee, G. (2012). Inter-rater reliability for the Medical Research Council sumscore to diagnose muscle weakness in critically ill patients. Critical Care, 16(Suppl 1), P412. https://doi.org/10.1186/cc10619
• Hermans, G., Van den Berghe, G., & Vanhorebeek, I. (2014). Intensive care unit-acquired weakness: An overview. Critical Care, 18(4), 216. https://doi.org/10.1186/cc13936
• Hough, C. L., Lieu, B. K., & Caldwell, E. S. (2011). Manual muscle strength testing of critically ill patients: Feasibility and inter-observer agreement. Critical Care, 15(1), R43. https://doi.org/10.1186/cc10005
• Kleyweg, R. P., van der Meché, F. G., & Schmitz, P. I. (1991). Interobserver agreement in the assessment of muscle strength in Guillain-Barré syndrome: The Medical Research Council scale. Muscle & Nerve, 14(11), 1103–1109. https://doi.org/10.1002/mus.880141111
• Medical Research Council. (1943). Aids to the examination of the peripheral nervous system (War Memorandum No. 7). H.M. Stationery Office.
• Medical Research Council. (1976). Aids to the examination of the peripheral nervous system (Memorandum No. 45). H.M. Stationery Office.
• Stevens, R. D., Marshall, J. C., Yoshida, T., Brower, R. G., Hall, J. B., Needham, D. M., Leff, B., Mrozek, S., & Sharshar, T. (2009). A framework for diagnosing and classifying intensive care unit-acquired weakness. Critical Care Medicine, 37(10 Suppl), S299–S308. https://doi.org/10.1097/CCM.0b013e3181b6ef67
• Vanhorebeek, I., Latronico, N., & Van den Berghe, G. (2020). ICU-acquired weakness. Intensive Care Medicine, 46(4), 637–653. https://doi.org/10.1007/s00134-020-05944-4

13. Items of the Scale (Questionnaire)