How do you assess leg strength in a physical exam?

Assessment of Leg Strength in Physical Examination

Leg strength should be assessed using the Medical Research Council (MRC) scale (0-5) for manual muscle testing, with specific attention to testing key muscle groups against gravity and resistance at standardized joint positions.

Manual Muscle Testing Using the MRC Scale

The MRC scale is the standard method for grading muscle strength in clinical settings:

• Grade 5 (Normal): Full range of motion against gravity with full resistance
• Grade 4 (Good): Full range of motion against gravity with some resistance
  • 4+: Slight weakness against resistance
  • 4: Moderate weakness against resistance
  • 4-: Significant weakness against resistance
• Grade 3 (Fair): Full range of motion against gravity but no resistance
• Grade 2 (Poor): Full range of motion with gravity eliminated (horizontal movement)
• Grade 1 (Trace): Visible or palpable muscle contraction but no movement
• Grade 0 (Zero): No contraction detected

Key Lower Extremity Muscle Groups to Test

When assessing leg strength, the following muscle groups should be systematically evaluated 1:

1. Hip Flexors: Patient in sitting position, instructed to lift thigh off examination table against resistance
2. Hip Extensors: Patient in prone position, instructed to lift leg upward while keeping knee extended
3. Hip Abductors: Patient in side-lying position, instructed to lift leg upward against resistance
4. Hip Adductors: Patient in supine position, instructed to bring legs together against resistance
5. Knee Extensors (Quadriceps): Patient in sitting position, instructed to extend knee against resistance
6. Knee Flexors (Hamstrings): Patient in sitting position, instructed to flex knee against resistance
7. Ankle Dorsiflexors: Patient in sitting position, instructed to pull foot upward against resistance
8. Ankle Plantarflexors: Patient in sitting position, instructed to push foot downward against resistance

Standardized Testing Positions

For accurate and reproducible measurements:

• Ensure proper patient positioning for each muscle group test
• Stabilize proximal joints to isolate the muscle group being tested
• Apply resistance at the distal end of the limb segment
• Test both sides for comparison of symmetry

Quantitative Strength Assessment

For more objective measurements, particularly in grade 4 where the MRC scale lacks sensitivity 2:

• Hand-held dynamometry: Provides numerical values of force production for specific muscle groups 3
• Fixed dynamometry: More accurate for stronger muscle groups like knee extensors 2

Functional Strength Testing

In addition to isolated muscle testing, functional strength tests provide valuable information about integrated muscle function 1:

• Single Leg Hop Test: Measures power and confidence in the limb
• Vertical Hop Test: Assesses vertical power generation
• Timed Up and Go: Evaluates functional mobility requiring adequate leg strength

Documentation Guidelines

Document strength findings with specificity:

• Record the MRC grade for each muscle group tested
• Note any asymmetry between sides (e.g., "Right knee extension 4/5, left 5/5")
• Document the specific position in which testing was performed
• Note any pain, compensation, or limitation during testing

Common Pitfalls to Avoid

• Inconsistent positioning: Maintain standardized positions for reproducible results
• Inadequate stabilization: Failure to stabilize proximal joints leads to compensation
• Excessive speed: Perform testing at moderate speed for accurate assessment
• Failure to detect bilateral weakness: Always compare to normative values, not just side-to-side
• Overlooking fatigue: Test major muscle groups first before fatigue sets in

By following this systematic approach to leg strength assessment, clinicians can accurately document muscle strength deficits and track changes over time, which is essential for diagnosis, treatment planning, and monitoring recovery.