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Strength of Individual Muscle Groups. Patterns of weakness can help localize a lesion to a particular cortical or white matter region, spinal cord level, nerve root, peripheral nerve, or muscle.

Test the strength of each muscle group and record it in a systematic fashion. Isolate the muscles being tested at each joint by supporting the joint on the proximal side as needed. It is wise to pair the testing of each muscle group immediately with testing of its contralateral counterpart to enhance detection of any asymmetries. Muscle strength is often rated on a scale of 0/5 to 5/5 as follows:

• 0/5: No contraction
• 1/5: Muscle flicker, but no movement
• 2/5: Movement possible, but not against gravity (test the joint in the horizontal plane)
• 3/5: Movement possible against gravity, but not against resistance by the examiner
• 4/5: Movement possible against some resistance by the examiner (sometimes this category is subdivided further into 4^–/5, 4/5, and 4⁺/5)
• 5/5: Normal strength

While testing muscle strength, it is important to keep in mind anatomical information such as which nerves, nerve roots, and brain areas control each muscle and to allow this information to guide the exam. Also, compare proximal versus distal weakness because these features can sometimes suggest muscle versus nerve disease, respectively.