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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:

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

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55. Detailed Hand Test

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56. Lower Extremity Test

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57. Foot Eversion, Inversion

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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.

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