Lesson 18: The Spine and Trunk Muscles

Spine Joint Actions, Muscles, and Exercises

Flexion (Sagittal Plane): A decrease in angle between two body parts. In the spine, flexion is bending forward.

• Muscles: Rectus abdominis, External obliques, Internal obliques, Psoas (if hips and pelvis are fixed)
• Exercises: Crunch, Reverse crunch, Planks (isometric flexion)

Extension (Sagittal Plane): An increase in angle between two body parts. In the spine, extension is bending backward.

• Muscles: Erector spinae, Multifidus, Latissimus dorsi
• Exercises: Hyper-extensions, Superman’s, Cobras, Yoga: Upward Facing Dog

Lateral Flexion (Frontal Plane): A frontal plane joint action of the spine that results in a decrease in the angle between two bones. Lateral flexion is the technical terminology for side-bending.

• Muscles Involved: Quadratus lumborum, External obliques, Internal obliques, Unilateral erector spinae
• Exercises: Side-bending, Side planks (isometric lateral flexion)

Rotation (Transverse Plane): Rotation refers to twisting or spinning of the bones of the spine around a vertical axis. For example, the motion of the cervical spine when signaling "no" with the head and neck.

• Muscles Involved: External obliques, Internal obliques, Multifidus, Erector spinae (possibly)
• Exercises: Up chops, Down chops, Russian twists, Oblique crunches

Course Summary

This course describes the landmarks and basic anatomy of the spine (vertebral column) and pelvis, the joint actions of the spine and motions of the pelvis, as well as an introduction to the spine and trunk muscles. The joints of the spine include the zygapophysial joints and vertebral disks, the joints of the pelvis include the sacroiliac joint (SIJ) and pubic symphysis, and the joints of the ribcage include the costovertebral joints at the thoracic spine and the sternocostal joints at the sternum.

The muscles covered include the rectus abdominis, external obliques, internal obliques, transverse abdominis, erector spinae, psoas, multifidus, quadratus lumborum (QL), and latissimus dorsi. This course includes a discussion of the joint actions, the contributing muscles, and practical examples of common exercises. For example, a chop pattern is primarily trunk rotation, which is the result of increased muscle activity of the external obliques, internal obliques, ipsilateral erector spinae, and contralateral multifidus. The abdominal crunch is an example of trunk flexion, and the result of force generated by the rectus abdominis, external obliques, internal obliques, and psoas. And, supermans include trunk extension, resulting from an isometric contraction of the multifidus, erector spinae, and potentially the latissimus dorsi. Note, the muscles of the trunk, are also referred to as “core muscles” and play an important role in maintaining optimal posture and optimal arthrokinematics of the trunk, pelvis, and ribcage.

Sports medicine professionals (personal trainers, fitness instructors, physical therapists, massage therapists, chiropractors, occupational therapists, athletic trainers, etc.) must know the anatomy and function of the trunk muscles and vertebral column for the analysis of human movement, and the development of sophisticated exercise programs and therapeutic (rehabilitation) interventions. Further, this course is essential knowledge for future courses discussing detailed anatomy like neural innervations (e.g. sacral plexus, femoral nerve, sciatic nerve), synergistic function of muscles (e.g. recruitment of trunk and hip muscles for spine stability), injury (e.g. low back pain, altered muscle activity, atrophy of the posterior muscles of the spine), and sports performance (e.g. best programming for optimizing trunk muscle strength and/or trunk muscle power).

This Course Includes:

• Video Lecture
• Study Guide
• Text of Material
• Learning Activities
• Planes and Exercises Table
• AI Tutor
• Practice Exam
• Continuing Education and Certification Approved Final Exam

Caption: The spinal segments of the vertebral column