From the Guidelines
The grading scale for assessing Motor Strength (Muscle Strength) is typically measured using the United Kingdom Medical Research Council System scale, which ranges from 0 to 5, with 0 indicating the lowest strength and 5 the highest 1.
Key Points
- The manual muscle test is used to measure muscle strength, with the MRC scale being a commonly used method to gauge muscle strength 1.
- The MRC scale is used to assess muscle groups bilaterally, including neck flexion/extension, shoulder abduction, elbow flexion/extension, wrist flexion/extension, hip flexion/extension, hip abduction/adduction, knee flexion/extension, ankle dorsiflexion, and plantar flexion 1.
- Other methods, such as quantitative myometry, may be used to assess muscle strength, particularly when the muscle strength is between 3-5 on the MRC scale 1.
- The MRC scale is widely used in clinical settings, including in the assessment of patients with stroke and muscular dystrophy 1.
Assessment Tools
- Manual muscle testing (MMT) is a commonly used assessment tool, with the MMT8 being a shortened version that scores the 8 proximal, distal, and axial muscle groups on one side 1.
- Other assessment tools, such as the Motricity Index and handheld dynamometry, may be used to assess muscle strength, particularly in patients with stroke 1.
From the Research
Grading Scale for Assessing Motor Strength
The grading scale for assessing motor strength, also known as muscle strength, is typically based on the Medical Research Council (MRC) scale, which ranges from 0 to 5 2, 3, 4, 5, 6. The scale is as follows:
- Grade 0: No contraction
- Grade 1: Flicker or trace of contraction
- Grade 2: Active movement, with gravity eliminated
- Grade 3: Active movement, against gravity
- Grade 4: Active movement, against gravity and resistance
- Grade 5: Normal strength
Comparison of Grading Scales
Studies have compared the MRC scale with other grading scales, such as the analogue scale, which expresses power as a percentage of the maximum expected for that muscle 2. The MRC scale has been found to be more reliable and accurate for assessing weak muscles, while the analogue scale is more reliable and accurate for assessing stronger muscles.
Limitations of the MRC Scale
The MRC scale has been criticized for its limitations, including poorly defined limits between grades '4' and '5' and large differences in the span of muscle strength encompassed by each grade 3. Attempts to modify the MRC scale, such as introducing an intermediate grade '4+', have not been shown to improve agreement between clinicians 3.
Inter-Rater Reliability
Studies have also examined the inter-rater reliability of the MRC scale, with significant dispersion in motor grading seen on example vignettes 4. The use of patient-reported outcome measures has also been found to be limited, with most respondents reporting not utilizing any patient-reported outcome measures across peripheral nerve pathologies 4.
Alternative Methods for Assessing Muscle Strength
Alternative methods for assessing muscle strength, such as hand-held myometry and isokinetic dynamometry, have been compared to the manual muscle test (MMT) 5. These methods have been found to be more sensitive and objective than the MMT, particularly for detecting small or moderate increases in strength over the course of rehabilitation.