Attachments, actions and innervation for the muscle-exam layer.
| Muscle | Key attachments | Action | Innervation |
|---|---|---|---|
| Rectus abdominis | Pubis → xiphoid/costal cartilages 5-7 | Trunk flexion; abdominal compression | Thoracoabdominal nerves |
| External oblique | Lower ribs → linea alba, pubic tubercle, iliac crest | Trunk flexion; contralateral rotation; ipsilateral sidebend | Thoracoabdominal nerves |
| Internal oblique | Thoracolumbar fascia/iliac crest/inguinal ligament → lower ribs/linea alba/pubis | Trunk flexion; ipsilateral rotation/sidebend | Thoracoabdominal + L1 |
| Transversus abdominis | Lower costal cartilage, thoracolumbar fascia, iliac crest/inguinal ligament → linea alba/pubis | Compresses/supports abdominal contents | Thoracoabdominal + L1 |
| Quadratus lumborum | Iliac crest/iliolumbar ligament → 12th rib/L1-L4 transverse processes | Ipsilateral sidebend; bilateral lumbar extension; fixes 12th rib | Anterior rami T12-L4 |
| Iliacus | Iliac fossa → lesser trochanter via iliopsoas tendon | Hip flexion | Femoral |
| Psoas major | T12-L5 vertebral bodies/discs/transverse processes → lesser trochanter | Hip flexion; trunk/hip stabilization, assists lateral flexion | Anterior rami lumbar nerves |
| Gluteus maximus | Posterior ilium/sacrum/coccyx → IT tract/gluteal tuberosity | Hip extension/lateral rotation | Inferior gluteal |
| Gluteus medius | Lateral ilium → greater trochanter | Hip abduction; pelvic stabilization; fiber-dependent rotation | Superior gluteal |
| Gluteus minimus | Lateral ilium → greater trochanter | Hip abduction/medial rotation; pelvic stabilization | Superior gluteal |
| TFL | ASIS/anterior iliac crest → IT tract | Hip flexion, abduction, medial rotation; assists knee stabilization through IT tract | Superior gluteal |
| Piriformis | Anterior sacrum → greater trochanter | Lateral rotation extended hip; abduction flexed hip | Nerve to piriformis |
| Obturator internus | Internal obturator membrane/bone → greater trochanter region | Lateral rotation; abducts flexed hip | Nerve to obturator internus |
| Superior gemellus | Ischial spine → with obturator internus tendon | Lateral rotation; abducts flexed hip | Nerve to obturator internus |
| Inferior gemellus | Ischial tuberosity → with obturator internus tendon | Lateral rotation; abducts flexed hip | Nerve to quadratus femoris |
| Quadratus femoris | Ischial tuberosity → intertrochanteric crest | Lateral rotation/adduction | Nerve to quadratus femoris |
| Obturator externus | External obturator membrane/bone → trochanteric fossa | Lateral rotation; stabilizes hip | Obturator |
| Rectus femoris | AIIS → tibial tuberosity via patella/patellar ligament | Knee extension + hip flexion | Femoral |
| Vastus lateralis/medialis/intermedius | Femur → tibial tuberosity via patella | Knee extension | Femoral |
| Sartorius | ASIS → medial proximal tibia | Hip flexion/abduction/lateral rotation; knee flexion | Femoral |
| Biceps femoris | Ischial tuberosity/femur → fibular head | Knee flexion/lateral rotation; long head hip extension | Sciatic: tibial division long head, common fibular division short head |
| Semitendinosus | Ischial tuberosity → medial proximal tibia | Hip extension; knee flexion/medial rotation | Tibial division sciatic |
| Semimembranosus | Ischial tuberosity → posterior medial tibial condyle | Hip extension; knee flexion/medial rotation | Tibial division sciatic |
| Adductor longus/brevis | Pubis → linea aspera | Hip adduction; assists flexion | Obturator |
| Adductor magnus | Pubis/ischium → linea aspera/adductor tubercle | Adduction; adductor part flexes, hamstring part extends hip | Obturator + tibial division sciatic |
| Gracilis | Pubis → medial proximal tibia | Hip adduction; knee flexion/medial rotation | Obturator |
| Pectineus | Superior pubic ramus → pectineal line femur | Hip adduction/flexion | Primarily femoral, sometimes obturator/accessory obturator contribution |
| Gastrocnemius | Femoral condyles → calcaneus via Achilles tendon | Plantarflexion; knee flexion | Tibial |
| Soleus | Posterior tibia/fibula → calcaneus via Achilles | Plantarflexion | Tibial |
| Plantaris | Lateral supracondylar femur → calcaneus | Weak plantarflexion/knee flexion | Tibial |
| Popliteus | Lateral femoral condyle → posterior tibia | Unlocks knee; assists medial tibial rotation | Tibial |
| Tibialis anterior | Lateral tibia/interosseous membrane → medial cuneiform/1st metatarsal | Dorsiflexion/inversion | Deep fibular |
| Tibialis posterior | Posterior tibia/fibula/interosseous membrane → navicular and other tarsal/metatarsal attachments | Plantarflexion/inversion; arch support | Tibial |
| Fibularis longus | Fibular head/lateral fibula → base 1st metatarsal/medial cuneiform plantar surface | Eversion; weak plantarflexion; arch support | Superficial fibular |
| Fibularis brevis | Lateral fibula → base 5th metatarsal | Eversion; weak plantarflexion | Superficial fibular |
| Fibularis tertius | Distal anterior fibula → base 5th metatarsal | Dorsiflexion/eversion | Deep fibular |
Protect femoral triangle, medial proximal thigh, sciatic pathway, popliteal fossa, fibular head/common fibular nerve and superficial vessels. The IT band is connective tissue, not a muscle. Unexplained unilateral hot/swollen/tender calf is a vascular red flag, not a “tight calf.”