Anatomy of musculoskeletal system
Upper extremity: muscle actions & innervation
The lists below are grouped by joint and motion: each motion names its prime movers and the peripheral nerves (with nerve roots, where listed) that supply them.
Shoulder, elbow, forearm, wrist, and hand motions with their muscles and nerves.
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), Lower subscapular (C5-C6), 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), Lower subscapular (C5-C6)
- 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, Thoracodorsal (C6-C8)
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 (pronator teres C6-C7; pronator quadratus via anterior interosseous, 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 (MCP, PIP) and profundus (MCP, PIP, DIP); lumbricals flex the MCP joints but extend the PIP and DIP joints
- Nerves: Median (all of FDS; lateral half of FDP and lateral two lumbricals), Ulnar (medial half of FDP and medial two lumbricals)
- Extension of fingers:
- Muscles: Extensor digitorum, extensor indicis, extensor digiti minimi
- Nerves: Radial (posterior interosseous)
- Thumb movements:
- Flexion/Opposition/Palmar abduction (abductor pollicis brevis): Median
- Extension/Radial abduction (abductor pollicis longus): Radial
- Adduction: Ulnar (adductor pollicis)
Lower extremity: muscle actions and innervation
The lists below follow the same pattern: each motion names its prime movers and the peripheral nerves (with nerve roots, where listed) that supply them.
Hip, knee, ankle, and toe motions with their muscles and nerves.
Hip
- Flexion:
- Muscles: Iliopsoas, rectus femoris, sartorius
- Nerves: Femoral (L2-L4); psoas major via direct branches of the lumbar plexus (L1-L3)
- 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); obturator externus via obturator nerve (L2-L4)
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 (gastrocnemius and soleus S1-S2; tibialis posterior L4-L5)
- 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 (L5-S2)
- Toe extension:
- Muscles: Extensor digitorum longus & brevis, extensor hallucis
- Nerves: Deep fibular (L5-S1)
Goniometry, range of motion, and outcome measures
ROM is measured with a goniometer: a fulcrum at the joint’s axis of rotation, a stationary arm aligned with the proximal segment, and a moving arm aligned with the distal segment. Stabilize the proximal segment first to prevent substitution.
Normal adult ROM for key joints.
| Joint | Motion | Normal ROM |
|---|---|---|
| Shoulder | Flexion | 0-180° |
| Shoulder | Abduction | 0-180° |
| Elbow | Flexion | 0-150° |
| Hip | Flexion | 0-120° |
| Knee | Flexion | 0-135° |
| Ankle | Dorsiflexion | 0-20° |
| Ankle | Plantarflexion | 0-50° |
Standardized self-report outcome measures track function over time. Common examples: DASH/QuickDASH (upper extremity), lower extremity functional scale (LEFS), Oswestry disability index (low back), and neck disability index (NDI) (cervical spine). The PTA administers these tools and records the score; interpreting the result remains the PT’s responsibility. Pain rating scales such as the Numeric Pain Rating Scale (NPRS) measure the subjective intensity of pain.
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
-
Position the patient
- Place the patient in a position that isolates the desired muscle/movement.
- Gravity-eliminated positions are used for weaker muscles.
-
Stabilize proximally
- Prevent substitution by stabilizing the joint or segment above.
-
Ask for active movement
- Instruct the patient to move the limb through full ROM without resistance.
-
Apply resistance
- Apply gradual, steady resistance opposite the movement direction.
- Resistance is typically applied distal to the joint being tested.
-
Palpate the muscle
- Palpate the muscle/tendon to confirm activation, especially in low-grade testing.
MMT grading scale (0-5)
MMT grades 0-5 with descriptions and criteria.
| 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 |
Test against gravity first. Full range against gravity → apply a break test (resistance at end range) to separate grade 3 from 4/5. Can’t complete full range against gravity → retest gravity-eliminated to separate grade 2 from 1/0. Modifiers: 3+ = full range against gravity with minimal resistance; 3- = more than half but less than full range against gravity; 2- = only partial range gravity-eliminated.
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 the 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: Side-lying, testing the top leg
- Motion: Lift leg into abduction
- Resistance: Applied at the lateral thigh
Knee extension (e.g., quadriceps)
- Position: Seated, knee at 90°
- Motion: Extend the 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 plantar flexion