Adam C. Stewart
Your core muscles have a central function, and targeting these muscles can lead to increased performance in a variety of exercises. Read this article to deepen your understanding of the basic function for performance and get programming recommendations to target your core muscles.
When people hear the term “abdominal muscles” in everyday speech, they often think of abdominals and obliques. These are indeed basic muscles, but basic muscles are made up of much more, and a thorough understanding of this topic can improve your ability to achieve your strength and physique goals. Technically, many muscles that work exclusively at the hip joint, such as the gluteus medius, are classified as core muscles (20). However, I have already discussed several of these hip muscles on Stronger By Science, so we will specifically look at the core core muscles, which have lumbar and thoracic functions.
Stem
The thoracic spine consists of 12 vertebrae that form the upper and middle skeletal back, while the lumbar spine consists of 5 vertebrae that form the lower skeletal back. Movements of the spine can occur in all three planes of movement at the joints formed between adjacent vertebrae (i.e. intervertebral joints).
In the sagittal plane, Flexion (i.e. rounding forward) and Extension (i.e. bulging backward) can occur. In the frontal plane, lateral bending (i.e. lateral bending) to the right or left can occur. In the transverse plane, rotation (that is, twisting) to one side or the other can occur. Compared to the lumbar intervertebral joints, the thoracic intervertebral joints have a much larger available transverse plane ROM (range of motion), but a lower sagittal plane ROM (78).
While the thoracic spine can move while the lumbar spine mainly maintains a fixed Position and vice versa, I will call the movement that occurs in both regions the trunk movement for convenience. Some muscles act exclusively on the intervertebral joints in one region and various trunk exercises can put more pressure on the muscles in one region than in another, but usually an exercise that trains one region can also be performed in such a way as to train the other. With regard to the ability of a particular central muscle to generate torque, a Variation can also exist in the multiple joints of the same region of the spine. For example, the psoas major has a greater leverage effect on the lateral flexion of the lower lumbar spine than the upper lumbar spine (41, 47). If you want to dive into the finer details of this Variation, you can read the biomechanical studies that I have cited, but I will not discuss this degree of Nuance in this article because it is not really relevant for practical application. As part of this article, I will surgically use the term “trunk” exclusively to describe the lumbar and thoracic region of the spine, which is different from the use of this term by other people. Some researchers define the trunk movement as “a compound movement involving the simultaneous rotation of the lumbar spine, pelvis and hips”, which would lead to the classification of the hip extensor muscles such as the gluteus maximus and the biarticular hamstrings as trunk extensors (91).
Of particular importance for understanding the functions of the trunk muscles is the fact that the right and left sides of a pair of trunk muscles can act on opposite sides of the same intervertebral joint. This can cause the right and left sides of a pair of muscles to act as antagonists (i.e. to face each other) in the Frontal and/or Transverse planes while acting unilaterally, but to act as synergists in the Sagittal plane (i.e. to contribute to the same function) while acting bilaterally. To clarify this concept, we compare the internal obliques to the biceps in a simplified example that hypothetically assumes that no other muscles are engaged, except for the muscles mentioned. When your right biceps contract while your right triceps are relaxed, your right elbow can bend, no matter how hard your left biceps contract, because your left and right biceps act on different elbow joints.
In this matter, the origin and approach of the right biceps are closer together, while the origin and approach of the right triceps (that is, The biceps antagonist) are further apart. However, if your right and left internal obliques produce the same force when they contract, the spine will not bend or turn sideways, because equal and opposite forces oppose each other in these planes. On the contrary, the bilateral internal oblique contraction causes the spinal column to flex forward in the sagittal plane, bringing the origins and approaches on both sides of the internal obliques closer together. If your right internal slash contracts while your left internal slash is relaxed, the spine may bend laterally to the right or turn to the right. Both are actions that cause the right internal slash to shorten while the left slash (that is, its antagonist) lengthens.
