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Strength of Individual Muscle Groups

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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. 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 its 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 anatomic 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. A detailed discussion of patterns of muscle weakness and localization is provided in Neuroanatomy through Clinical Cases Key Clinical Concepts 6.3, and in Chapters 8 and 9. In the tables below we briefly summarize some of the main actions, muscle groups, peripheral nerves, and nerve roots tested during the motor exam.

54. Upper Extremity Strength

55. Detailed Hand Test

56. Lower Extremity Test

57. Foot Eversion, Inversion

Upper Extremity Strength Testing

Action	Muscles	Nerves	Nerve Roots
Finger extension	Extensor digitorum, Extensor indicis, Extensor digiti minimi	Radial nerve (posterior interosseous nerve)	C7, C8
Thumb abduction in plane of palm	Abductor pollicis longus	Radial nerve (posterior interosseous nerve)	C7, C8
Finger abduction	Dorsal interossei, Abductor digiti minimi	Ulnar nerve	C8, T1
Finger and thumb adduction in plane of palm	Adductor pollicis, Palmar interossei	Ulnar nerve	C8, T1
Thumb opposition	Opponens pollicis	Median nerve	C8, T1
Thumb abduction perpendicular to plane of palm	Abductor pollicis brevis	Median nerve	C8, T1
Flexion at distal interphalangeal joints digits 2, 3	Flexor digitorum profundus to digits 2, 3	Median nerve	C7, C8
Flexion at distal interphalangeal joints digits 4, 5	Flexor digitorum profundus to digits 4, 5	Ulnar nerve	C7, C8
Wrist flexion and hand abduction	Flexor carpi radialis	Median nerve	C6, C7
Wrist flexion and hand adduction	Flexor carpi ulnaris	Ulnar nerve	C7, C8, T1
Wrist extension and hand abduction	Extensor carpi radialis	Radial nerve	C5, C6
Elbow flexion (with forearm supinated)	Biceps, Brachialis	Musculocutaneous nerve	C5, C6
Elbow extension	Triceps	Radial nerve	C6, C7, C8
Arm abduction at shoulder	Deltoid	Axillary nerve	C5, C6

Lower Extremity Strength Testing

Action	Muscles	Nerves	Nerve Roots
Hip flexion	Iliopsoas	Femoral nerve, and L1-L3 nerve roots	L1, L2, L3, L4
Knee extension	Quadriceps	Femoral nerve	L2, L3, L4
Knee flexion	Hamstrings (semitendinosus, semimembranosus, biceps femoris)	Sciatic nerve	L5, S1, S2
Leg abduction	Gluteus medius, Gluteus minimus, Tensor fasciae latae	Superior gluteal nerve	L4, L5, S1
Leg adduction	Obturator externus, Adductor longus, magnus, and brevis, Gracilis	Obturator nerve	L2, L3, L4
Toe dorsiflexion	Extensor hallucis longus, Extensor digitorum longus	Deep peroneal nerve	L5, S1
Foot dorsiflexion	Tibialis anterior	Deep peroneal nerve	L4, L5
Foot plantar flexion	Triceps surae (gastrocnemius, soleus)	Tibial nerve	S1, S2
Foot eversion	Peroneus longus, Peroneus brevis	Superficial peroneal nerve	L5, S1
Foot inversion	Tibalis posterior	Tibal nerve	L4, L5

When more than one nerve root participates in an action, emphasis indicates the most important nerve roots.