L5.5.5.2: Lower Back

• LOWER BACK

  • Erector Spinae

  [a] Trapezius

  [b] Latissimus Dorsi

  [c] Lumbodorsal Fascia / Thoracolumbar Fascia (not a muscle)

  [d] Serratus Posterior Inferior

  [e] Gluteus Maximus

  
• Latissimus Dorsi

  ○ 2 large flat muscles

  ○ Cover the lower back

  ○ Originate on the lower spine and ilium and then sweep superiorly

  ○ Insert into the proximal end of the humerus

  ○ Extends and adducts the humerus

  ○ Important muscles when the arm must be brought down in a power stroke (like swimming or striking a blow)
• Erector Spinae

  ○ Prime mover of back extension

  ○ Paired muscles that are deep in the back

  ○ Composite muscle containing 3 muscle columns

  ■ Longissimus

  ■ Iliocostalis

  ■ Spinalis

  ○ Act as powerful back extensors (erectors)

  ○ Provide resistance that helps control the action of bedding over at the waist

  ○ Go into spasms, common source of lower back pain
• Lumbodorsal Fascia / Thoracolumbar Fascia (not a muscle)

  ○ Deep investing membrane that covers the deep muscles of the back of the trunk
• Serratus Posterior Inferior

  ○ Originates from the spinous processes of the T11 to T12 vertebrae

  ○ Has its insertion on the four lower ribs

  ○ Known to be among the secondary back muscles, meaning that they migrated to the back in the course of embryogenesis
• Gluteus Maximus

  ○ Superficial muscle of the hip that forms most of the flesh of the buttock

  ○ Powerful hip extensor that acts to bring the thigh in a straight line with the pelvis

  ○ Not important in walking, but the most important muscle for extending the hip when power is needed (like climbing the stairs or jumping)

  ○ Originates from the sacrum and iliac bones and inserts on the gluteal tuberosity of the femur and into the large tendinous iliotibial tract