The Erector Spinae Group is a group of 3 sets of muscles—spinalis, longissimus, and iliocostalis. The spinalis group are located off of the spinous processes of the vertebrae. The longissimus group are located off of the transverse processes of the vertebrae and the iliocostalis group are located off of the ribs. By knowing these regions we can see that the spinalis group is the most medial and the iliocostalis group is most lateral.
1 During full flexion the erector spinae are relaxed. When standing upright the muscles are active and extension is initiated by the hamstrings—so when you lift a load from the bent over position it causes injury to the erector spinae group. Always lift with a straight back, not when you are hunched over.
2 3 The interspinalis muscles are very tiny muscles that connect from one spinous process to another. The intertransversarii muscles connect between each transverse process. The multifidus lies deep to the erector spinae muscles and it connects from one transverse process to the next spinous process.
4 The rotatores differs from the multifidus by going from 1 transverse process to 2 spinous processes.
5 The external obliques are the most superficial of the oblique muscles. Notice the fibers angle downward and medially, which allows for lateral flexion to same side and rotation to the opposite side. What other muscle does that (neck muscle)?? Once again it takes both sides to contract to cause trunk flexion to occur and only 1 side to cause the rotation and lateral flexion. Now the internal obliques have the fibers directed more horizontally which allows for rotation to the same side when 1 side contracts unlike the external obliques. The internal obliques are important during forced expiration, coughing, and sneezing.
6 The rectus abdominis is the primary ab muscle and is used during sit-ups and leg raises while lying down. The tendinous bands divide each rectus into 4 bellies—8 total. The transversus abdominis is the deepest of the obliques and rectus abdominis and runs transversally. This muscle is used for compression of the viscera; or in other words, keep everything (internal organs) in place.
7 8 9 10 This is a 4-sided muscle (“quadrate”) in the lumbar region so it’s name gives it away. The quadratus lumborum also helps to stabilize the lumbar vertebrae as well as assisting in forced expiration.
11 The diaphragm is very deep and is the most important muscle of inspiration. Pressure changes occur in the diaphragm to help the blood return to the heart. Larger volume = less pressure. The external intercostals aid in inspiration and their fibers are oriented obliquely down and forward toward the costal cartilage. The internal intercostals aid in forced expiration and their fibers are oriented obliquely away from the costal cartilage.
12 13 By increasing the thoracic cavity, it helps with inspiration. Now remember the scalene group from the neck muscles (cervical region)—they help with inspiration by raising the 1st rib, which increases the thoracic cavity which leads to inspiration. The Serratus Posterior (superior fibers) muscle raises the ribs during inspiration.
14 The transversus thoracis is found on the inside of the rib cage and by depressing the ribs, it decreases the thoracic cavity, which helps with forced expiration. The inferior fibers of the serratus posterior also do rib depression.
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