From the Guidelines
In a neurological exam, strength and power are quantified using the Medical Research Council (MRC) scale, which grades muscle strength from 0 to 5, as recommended by the most recent guidelines 1. This scale is a widely accepted and reliable method for assessing muscle strength, with a score of 0 indicating no muscle contraction, 1 showing visible contraction without movement, 2 meaning movement with gravity eliminated, 3 indicating movement against gravity, 4 representing movement against resistance but less than normal, and 5 being normal strength. The examiner tests major muscle groups bilaterally by having the patient perform specific movements against resistance, such as:
- Shoulder abduction
- Elbow flexion/extension
- Wrist flexion/extension
- Hip flexion/extension
- Knee flexion/extension
- Ankle dorsiflexion/plantarflexion Power assessment involves evaluating both the force generated and the speed of muscle contraction. When documenting findings, it's essential to note any:
- Asymmetry between sides
- Proximal versus distal weakness patterns
- Specific muscle group deficits These patterns help localize neurological lesions, as upper motor neuron problems typically cause spastic weakness while lower motor neuron issues result in flaccid weakness. Quantifying strength objectively helps track disease progression and treatment effectiveness over time, as supported by studies such as 1 and 1. Additionally, other assessment tools like the Fugl-Meyer Motor Assessment 1 and the Wolf Motor Function Test 1 can be used to evaluate sensorimotor impairment and UE function, but the MRC scale remains the most straightforward and widely used method for quantifying strength and power in a neurological exam.
From the Research
Quantifying Strength in a Neurological Exam
- The Medical Research Council (MRC) scale is a commonly used method to grade muscle power, with scores ranging from 0 to 5 2.
- The MRC scale is more reliable and accurate for assessing weak muscles (grades 0-3), while an analogue scale is more reliable for assessing stronger muscles (grades 4 and 5) 2.
- A modified MRC grading system, developed through Rasch analyses, has been proposed to improve clinicians' ability to differentiate among response categories 3.
Quantifying Power in a Neurological Exam
- Nerve conduction studies (NCS) and electromyography (EMG) can be used to quantify nerve conduction velocity and muscle function 4.
- Repetitive nerve stimulation (RNS) can identify defects in neuromuscular junction transmission, and needle EMG can detect myopathic changes in muscle and signs of denervation 4.
- Quantitative strength measurements, such as those used in motor neuron disease research, can provide reliable and sensitive indicators of disease progression and therapeutic effects 5.
Standardization of Strength Measurements
- Standardization of grip strength measurements can improve repeatability and peak force, with protocol B (comfortable arm position and challenging stimulus) showing the highest peak values 6.
- The use of a strain-gauge dynamometer and standardized measurement protocols can help to ensure reliable and accurate strength measurements 6.