Anatomy of musculoskeletal system

Upper extremity: muscle actions & innervation

Shoulder

• Flexion:
  • Muscles: Anterior deltoid, coracobrachialis, biceps brachii
  • Nerves: Axillary (C5-C6), Musculocutaneous (C5-C7)
• Extension:
  • Muscles: Posterior deltoid, latissimus dorsi, teres major, triceps (long head)
  • Nerves: Axillary (C5-C6), Thoracodorsal (C6-C8), Radial (C6-C8)
• Abduction:
  • Muscles: Supraspinatus, middle deltoid
  • Nerves: Suprascapular (C5-C6), Axillary (C5-C6)
• Adduction:
  • Muscles: Pectoralis major, latissimus dorsi, teres major
  • Nerves: Medial/lateral pectoral (C5-T1), Thoracodorsal (C6-C8)
• External rotation:
  • Muscles: Infraspinatus, teres minor
  • Nerves: Suprascapular (C5-C6), Axillary (C5-C6)
• Internal rotation:
  • Muscles: Subscapularis, pectoralis major, latissimus dorsi
  • Nerves: Upper/lower subscapular (C5-C7), Medial/lateral pectoral

Elbow

• Flexion:
  • Muscles: Biceps brachii, brachialis, brachioradialis
  • Nerves: Musculocutaneous (C5-C6), Radial (C5-C6)
• Extension:
  • Muscles: Triceps brachii, anconeus
  • Nerves: Radial (C6-C8)

Forearm

• Supination:
  • Muscles: Biceps brachii, supinator
  • Nerves: Musculocutaneous (C5-C6), Radial (C6-C7)
• Pronation:
  • Muscles: Pronator teres, pronator quadratus
  • Nerves: Median (C6-C7, C7-C8)

Wrist

• Flexion:
  • Muscles: Flexor carpi radialis & ulnaris, palmaris longus
  • Nerves: Median (FCR, PL), Ulnar (FCU)
• Extension:
  • Muscles: Extensor carpi radialis longus/brevis, extensor carpi ulnaris
  • Nerves: Radial (C6-C8)

Hand

• Flexion of fingers (MCP, PIP, DIP):
  • Muscles: Flexor digitorum superficialis/profundus, lumbricals
  • Nerves: Median (lateral hand), Ulnar (medial hand)
• Extension of fingers:
  • Muscles: Extensor digitorum, extensor indicis, extensor digiti minimi
  • Nerves: Radial (posterior interosseous)
• Thumb movements:
  • Flexion/Opposition: Median
  • Extension/Abduction: Radial
  • Adduction: Ulnar (adductor pollicis)

Lower extremity: muscle actions and innervation

Hip

• Flexion:
  • Muscles: Iliopsoas, rectus femoris, sartorius
  • Nerves: Femoral (L2-L4)
• Extension:
  • Muscles: Gluteus maximus, hamstrings
  • Nerves: Inferior gluteal (L5-S2), Sciatic (L5-S2)
• Abduction:
  • Muscles: Gluteus medius & minimus, TFL
  • Nerves: Superior gluteal (L4-S1)
• Adduction:
  • Muscles: Adductors (longus, brevis, magnus), gracilis
  • Nerves: Obturator (L2-L4)
• Internal rotation:
  • Muscles: Gluteus medius/minimus (anterior fibers), TFL
  • Nerves: Superior gluteal (L4-S1)
• External rotation:
  • Muscles: Piriformis, gemelli, obturators, quadratus femoris
  • Nerves: Sacral plexus (L5-S2)

Knee

• Flexion:
  • Muscles: Hamstrings (biceps femoris, semitendinosus, semimembranosus)
  • Nerves: Sciatic (L5-S2)
• Extension:
  • Muscles: Quadriceps (rectus femoris, vasti muscles)
  • Nerves: Femoral (L2-L4)

Ankle

• Plantarflexion:
  • Muscles: Gastrocnemius, soleus, tibialis posterior
  • Nerves: Tibial (S1-S2)
• Dorsiflexion:
  • Muscles: Tibialis anterior, extensor hallucis longus
  • Nerves: Deep fibular (L4-S1)
• Inversion:
  • Muscles: Tibialis anterior & posterior
  • Nerves: Deep fibular (TA), Tibial (TP)
• Eversion:
  • Muscles: Peroneus longus & brevis
  • Nerves: Superficial fibular (L5-S1)

Toes

• Toe flexion:
  • Muscles: Flexor digitorum longus & brevis, flexor hallucis
  • Nerves: Tibial (S2-S3)
• Toe extension:
  • Muscles: Extensor digitorum longus & brevis, extensor hallucis
  • Nerves: Deep fibular (L5-S1)

Manual muscle testing (MMT) overview

MMT is used to assess the strength of a specific muscle or muscle group. The test is done by isolating the muscle’s action, asking the patient to contract it, and then applying resistance to gauge its strength.

How to perform MMT

1. Position the patient

   • Place the patient in a position that isolates the desired muscle/movement.
   • Gravity-eliminated positions are used for weaker muscles.

2. Stabilize proximally

   • Prevent substitution by stabilizing the joint or segment above.

3. Ask for active movement

   • Instruct the patient to move the limb through full ROM without resistance.

4. Apply resistance

   • Apply gradual, steady resistance opposite the movement direction.
   • Resistance is typically applied distal to the joint being tested.

5. Palpate muscle

   • Palpate the muscle/tendon to confirm activation, especially in low-grade testing.

MMT grading scale (0–5)

Grade	Description	Criteria
5	Normal (N)	Full ROM against gravity, maximal resistance
4	Good (G)	Full ROM against gravity, moderate resistance
3	Fair (F)	Full ROM against gravity, no resistance
2	Poor (P)	Full ROM in gravity-eliminated position, no resistance
1	Trace (T)	No movement, but palpable or visible muscle contraction
0	Zero (0)	No contraction, no movement or muscle activity

MMT positions by major muscle groups (examples)

Shoulder Flexion (e.g., anterior deltoid)

• Position: Seated or supine
• Motion: Shoulder flexion to 90°
• Resistance: Applied just above elbow, downward

Elbow flexion (e.g., biceps brachii)

• Position: Seated, arm at side
• Motion: Flex elbow with palm up
• Resistance: Distal forearm, pulling down

Hip Abduction (e.g., gluteus medius)

• Position: Sidelying, testing top leg
• Motion: Lift leg into abduction
• Resistance: Applied at lateral thigh

Knee extension (e.g., quadriceps)

• Position: Seated, knee at 90°
• Motion: Extend knee fully
• Resistance: Anterior distal leg, pushing into flexion

Ankle dorsiflexion (e.g., tibialis anterior)

• Position: Seated or supine
• Motion: Dorsiflexion & inversion
• Resistance: Top of foot, pushing into plantarflexion