Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse.
Authors: Dietrich Johanna, Handschuh Stephan, Steidl Robert, Böhler Alexandra, Forstenpointner Gerhard, Egerbacher Monika, Peham Christian, Schöpper Hanna
Journal: Animals : an open access journal from MDPI
Summary
# Muscle Fibre Architecture of the Equine Longissimus Dorsi The longissimus dorsi is the horse's largest back muscle and critical to spinal stability and performance, yet detailed information about its internal organisation has remained limited until now. Researchers dissected five cadaveric equine backs in layered sections, digitally mapping individual muscle fibre bundles from origin to insertion and creating 3D reconstructions combined with CT imaging to measure fascicle length, pennation angles, muscle volume and physiological cross-sectional area (PCSA) across functional compartments. Fascicle length decreased substantially along the spine—from maximum values in the thorax to just 50% of that length in caudal compartments—whilst pennation angles to the horizontal plane shifted dramatically from near-parallel alignment cranially (0°) to 38° in caudal regions, with variable sagittal plane angles of 0–22° in posterior compartments. Muscle volume ranged from 1350–4700 cm³ and PCSA from 219–700 cm² depending on body size and compartmental fascicle length. These systematic architectural variations along the longissimus suggest regional differences in contraction behaviour that have direct implications for how the muscle functions under saddle, influences spinal support, and potentially relates to back dysfunction and performance issues—making this anatomical foundation essential for developing biomechanical models that can predict muscle function and inform clinical assessment of back problems in practice.
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Practical Takeaways
- •The longissimus dorsi shows distinct regional architecture with different mechanical properties along the thoracolumbar spine; understanding these differences helps explain regional variation in back dysfunction and response to therapy.
- •Cranial thoracic fascicles are longer with minimal pennation angles, favouring longitudinal force generation for spinal stability, while caudal fascicles have increased pennation and shorter lengths, suggesting different functional roles in lateral or rotational movements.
- •Individual variation in muscle volume and fascicle properties based on body type and age should inform assessment and rehabilitation strategies for horses with back pain or performance issues.
Key Findings
- •Fascicle length in thoracic longissimus dorsi is highest cranially and decreases caudally, with lumbar fascicles measuring ~75% of thoracic values and caudal compartments <50%.
- •Pennation angles to the horizontal plane increase from ~0° in cranial compartments to mean 38° in caudal compartments, indicating systematic architectural variation.
- •Muscle volume ranges 1350-4700 cm³ and PCSA ranges 219-700 cm² depending on body size and mean fascicle length.
- •Fascicles in thoracic compartments run nearly parallel to the spine, while caudal compartments show 0-22° pennation angles to the sagittal plane, suggesting distinct regional contraction mechanics.