01/26/2026
🐴As the longissimus dorsi muscle is the largest muscle in the equine back, it has great influence on the stability of the spine.
🐴It starts on the 4th cervical vertebra and attaches to each cervical vertebra after the the 4th. It also attaches to every single vertebra down through the lumbar region. It doesn't stop here, though. Its fascia extends into the sacrum and into other muscles. That's a story for another day.
🐴It's action is to create extension in the back...Yep that's right, it's not for rounding or collection. Like the roan horse in the 2nd image. Look at that extension!
🐴The main job of this muscle is to transfer force from the hindquarters forward to the rest of the body.
🐴You can feel this muscle on your horse. It should be nice and rounded up, not dished in or concave. You can feel it in action when you ride ba****ck.
🐴It can be very atrophied in many horses' backs. The last photo is an image of many of the backs we see. The back is slightly sloped, and the longissimus muscle is very concave.
