How do you assess muscular strength in a physical exam?

Assessment of Muscular Strength in Physical Examination

Muscular strength should be assessed using the Medical Research Council (MRC) scale, which grades strength from 0-5, with manual muscle testing performed on key muscle groups bilaterally in a standardized position. 1

MRC Scale for Manual Muscle Testing

The MRC scale is the most widely used standardized method for assessing muscle strength in clinical settings:

• 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 (but weaker than normal)
• Grade 5: Normal strength

Key Points About the MRC Scale

• The scale has inherent limitations, particularly in the upper range between grades 4 and 5, where there is a large span of muscle strength encompassed 2
• Some clinicians use intermediate grades like "4+" to describe strength that is better than grade 4 but not quite normal 2
• For more precise measurements in the 4-5 range, quantitative dynamometry is recommended 3

Standardized Approach to Muscle Testing

1. Patient Positioning: Position the patient appropriately with proper support (e.g., elbows supported for upper extremity testing) 4

2. Bilateral Testing: Test corresponding muscle groups on both sides for comparison 1

3. Key Muscle Groups to Test:

   • Upper Extremities: Neck flexion/extension, shoulder abduction, elbow flexion/extension, wrist flexion/extension 1
   • Lower Extremities: Hip flexion/extension, hip abduction/adduction, knee flexion/extension, ankle dorsiflexion, and plantar flexion 1

4. Testing Technique:

   • Apply resistance in the opposite direction of the muscle action
   • Apply resistance gradually rather than suddenly
   • Stabilize proximal segments to isolate specific muscle groups
   • Maintain consistent testing positions across examinations

Quantitative Strength Assessment Methods

For more objective measurements, especially in research or when tracking changes over time:

1. Hand Dynamometry:

   • Calibrated hand dynamometer provides reliable assessment of grip strength 4
   • Patient should be positioned with elbows supported 4
   • Results should be compared to age and sex-specific reference values 4

2. Other Quantitative Methods:

   • Motricity Index: Tests strength at 3 key upper extremity and 3 key lower extremity segments, yielding a score from 0-100 1
   • Handheld dynamometry for specific muscle groups 1

Documentation and Serial Assessment

• Record strength for each muscle group tested using the MRC scale
• Note any asymmetry between sides
• For serial assessments, use consistent testing positions and techniques
• Consider using standardized forms to document findings systematically

Common Pitfalls to Avoid

• Inconsistent Testing Position: Variations in patient positioning can significantly affect results
• Inadequate Stabilization: Failure to stabilize proximal segments can lead to compensation by other muscle groups
• Applying Uneven Resistance: Inconsistent application of resistance affects reliability
• Overlooking Fatigue: Muscle strength may decrease with repeated testing due to fatigue
• Relying Solely on MRC Scale: For subtle changes or in the 4-5 range, quantitative methods provide better sensitivity 3

For comprehensive assessment of neuromuscular function, muscle strength testing should be combined with other assessments such as range of motion, tone, and functional testing to provide a complete clinical picture.