Assessment and Scoring of Muscle Power in Upper and Lower Limbs
Use the Medical Research Council (MRC) scale as your primary tool for manual muscle testing in both upper and lower extremities, testing specific muscle groups systematically and scoring each on the 0-5 scale. 1
The MRC Scale Scoring System
The MRC scale grades muscle strength from 0 to 5 based on the following criteria:
- Grade 0: No visible muscle contraction 2
- Grade 1: Visible or palpable muscle contraction, but no movement 2
- Grade 2: Movement possible with gravity eliminated (limb moves in horizontal plane) 2
- Grade 3: Movement against gravity through full range of motion, but cannot overcome any additional resistance 2, 3
- Grade 4: Movement against gravity with some resistance, but weaker than normal 2, 3
- Grade 5: Normal strength against full resistance 2, 3
Specific Muscle Groups to Test
Upper Extremity Assessment
Test these key muscle groups bilaterally: 1
- Shoulder abduction/flexion
- Elbow flexion and extension
- Wrist extension and flexion
- Long finger flexors
- Hand grip
Lower Extremity Assessment
Test these key muscle groups bilaterally: 1
- Hip flexion and extension
- Knee extension and flexion
- Ankle dorsiflexion and plantarflexion
- Hamstrings
- Gastrocnemius
Testing Technique and Positioning
Position the patient appropriately for each muscle group, stabilize proximal joints, and apply resistance perpendicular to the limb segment being tested. 1
- For grades 0-2: Test with gravity eliminated (patient positioned horizontally) 2, 3
- For grades 3-5: Test against gravity with the limb in vertical plane 2, 3
- Apply manual resistance progressively for grades 4-5 3
Important Clinical Considerations
The MRC scale is most reliable and accurate for weak muscles (grades 0-3), while quantitative methods like handheld dynamometry are superior for stronger muscles (grades 4-5). 2
When to Use Alternative Methods
- For muscles grading 3-5 on MRC scale: Consider quantitative myometry or handheld dynamometry for more precise measurements 1
- In ICU settings: Use the six-point MRC score across 12 muscle groups (6 upper limb, 6 lower limb); a sum score <48 defines ICU-acquired weakness 1
- For cooperative patients: Handheld dynamometry shows excellent interobserver reliability (ICC >0.90) and can detect subtle changes 4
Key Muscle Groups for ICU Assessment
When performing comprehensive MRC scoring in critically ill patients, test three muscle groups per limb bilaterally (total of 12 muscle groups): 1
- Upper limbs: Shoulder abduction, elbow flexion, wrist extension
- Lower limbs: Hip flexion, knee extension, ankle dorsiflexion
Common Pitfalls to Avoid
Do not rely solely on the MRC scale for grades 4-5, as it lacks precision in this range and has poor discrimination between "strong but not normal" and "normal" strength. 2, 3
- The MRC scale grade 4 is particularly problematic with wide variability 2, 3
- Adequate training is required for reliable MRC scoring 1
- Testing requires patient cooperation and ability to follow commands 1
- Ensure proper stabilization to isolate the muscle group being tested 3
Complementary Functional Assessment
Supplement strength testing with handgrip dynamometry as a simple, reliable measure of overall muscle function and nutritional status. 1, 5
- Handgrip strength <10 kg at discharge predicts increased mortality risk 1, 5
- Can identify muscle dysfunction before body composition changes become apparent 1, 5
- Requires well-calibrated dynamometer adjusted for hand size 1
Frequency of Assessment
Test upper and lower extremity strength every 6 months in ambulatory patients, and consider more frequent testing (every 4 months) when monitoring disease progression or treatment response. 1