Mrc Grading of power
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MRC grading of muscle power scale clinical neurology
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Here is a complete overview of the MRC Grading of Muscle Power:
MRC (Medical Research Council) Scale for Muscle Power
Originally described in Aids to the Investigation of Peripheral Nerve Injuries (War Memorandum No. 7, 1943), the MRC scale is the most widely accepted clinical tool for grading muscle strength. It is also called the Oxford Scale.
The Six Grades (0-5)
| Grade | Description |
|---|---|
| 0 | No movement - complete paralysis, no visible or palpable contraction |
| 1 | Flicker of movement - trace contraction seen or felt, but no joint movement |
| 2 | Active movement with gravity eliminated - full range of motion only when gravity is removed (limb supported horizontally) |
| 3 | Active movement against gravity - can complete full range of motion against gravity, but no added resistance |
| 4 | Active movement against resistance, but power less than full - can resist examiner but weaker than normal |
| 5 | Normal power - full strength against maximal resistance |
Grade 4 Subdivision (commonly used in clinical practice)
Grade 4 covers a wide range of muscle strength, so it is often subdivided:
| Subgrade | Meaning |
|---|---|
| 4- | Movement against slight resistance |
| 4 | Movement against moderate resistance |
| 4+ | Movement against strong resistance, just below normal |
How to Test Muscle Power
- Ask the patient to perform the movement actively
- First test against gravity (to distinguish grade 2 from grade 3)
- Then apply resistance (to distinguish grades 3, 4, and 5)
- Palpate the muscle belly or tendon simultaneously to confirm which muscle is contracting - this is especially important where synergistic muscles exist (e.g., elbow flexion can be performed by biceps, brachialis, or brachioradialis)
Clinical Pearls
- Grade 4 is NOT mild weakness - a patient who is diffusely 4/5 has significant, clinically important weakness, not just minor involvement
- The scale is intentionally coarse - it is easy to apply at the bedside without special equipment
- Grade 4 in particular spans a wide range of strength, which is the rationale for the 4-, 4, 4+ subdivision
- For research or outcome tracking, formal dynamometry is preferable to the MRC scale alone
MRC Sum Score (MRC-SS)
For assessing generalised weakness (e.g., Guillain-Barre syndrome, ICU-acquired weakness), six muscle groups are tested bilaterally (total 12 groups), giving a maximum score of 60:
| Muscle Group | Nerve Root |
|---|---|
| Shoulder abduction | C5 |
| Elbow flexion | C5-C6 |
| Wrist extension | C6-C7 |
| Hip flexion | L2-L3 |
| Knee extension | L3-L4 |
| Ankle dorsiflexion | L4-L5 |
An MRC-SS < 48/60 is the accepted cut-off for diagnosing ICU-acquired weakness.
Sources: Bailey and Love's Short Practice of Surgery 28th Ed., Table 35.4; Rockwood and Green's Fractures in Adults 10th Ed., Table 20-2; Physiopedia - Oxford Scale; StatPearls - Muscle Strength Grading
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