The “core” is a hot topic among fitness enthusiasts, sports performance advocates, and medical professionals treating low back pain. Core stability and core strength are terms that are often used interchangeably when speaking about strengthening and training the muscles of the torso/trunk. The two terms are, in fact, quite different is their meaning.
Training for core stability requires resisting motion at the lumbar spine through activation of the abdominal muscles together in concert. Training for core strength allows for motion through the lumbar spine in an attempt to work the abdominal muscles (often times in an isolated manner). As it relates to fitness and sport, popular programs and “schools of thought” (i.e. pilates, yoga, TRX, ViPR, exergaming) follow core stability and strengthening principles as a foundation of their methods.
Understanding the Core
The core can be described as a muscular box (with the abdominals in the front, spinal muscles and gluteals in the back, the diaphragm as the roof, and the pelvic floor and hip girdle muscles at the bottom). This box holds 29 pairs of muscles that help to stabilize the spine, pelvis, and muscles, connective tissue and bones of the kinetic chain during functional movements. Without these muscles, the spine would become unstable due to compressive forces and gravity. When the musculoskeletal system works properly, proper force distribution and maximum force generation (with minimal compressive, translational, or shearing forces at the joints of the kinetic chain) is possible. This is especially important in sports and multidirectional activities.
The thoracolumbar fascia is a deep membrane in the torso that covers the deep muscles of the back of the trunk (also known as “nature’s back belt”). It is the transitional area between the lower and upper body where forces are transferred during movement. Without it, total body movement would not be possible because it connects many joint systems and provide an anchor by which muscles produce force.
Two types of muscle fibers make up the core: slow-twitch and fast-twitch. Slow-twitch fibers primarily make up the deep muscle layer. These muscles are shorter in length and are suited for responding to changes in posture and additional loads on the extremities. Muscles include the transversus abdominis, multifidus, internal oblique, and the pelvic floor muscles.
In contrast, fast-twitch fibers comprise the superficial muscles of the body. These muscles are longer and produce large amounts of torque in gross motor movements. Muscles include the erector spinae, external oblique, rectus abdominis, and quadratus lumborum (a major stabilizer of the spine).
The abdominals make up an essential part of the core. The transversus abdominis primarily responsible for stabilizing the spine. It has fibers that run horizontally, creating a belt around the abdomen. ‘‘Hollowing in’’ of the abdomen creates isolated activation of the transversus abdominis. The transversus abdominis and multifidus have been shown to contract 30 milliseconds before movement of the shoulder and 110 ms before movement of the leg in healthy people, indicating their role in stabilizing joints prior to movement. The internal oblique and the transversus abdominis work together to increase the intra-abdominal pressure through the thoracolumbar fascia, to reinforce the spine. The external oblique, the largest and most superficial abdominal muscle, acts to decrease anterior pelvic tilt and maintain a neutral posture.
The hip musculature is movement related to walking, playing a key role in stabilizing the trunk and pelvis. Muscle groups include hip extensors (gluteus maximus), hip flexors (rectus femurs, sartorius, ), adductor muscles (adductor brevis, adductor longus, adductor magnus, pectineus, gracilis), and abductor muscles (tensor fasciae latae, gluteus maximus, gluteus medius).
The diaphragm serves as the “roof” of the core complex, while the pelvic floor serves as the “floor”. The diaphragm plays a key role as it increases intra-abdominal pressure during movement to enhance spinal stability. Pelvic floor muscles are activated together with transversus abdominis contraction. Because both muscles reinforce safety during movement, in addition to alleviating low back pain, diaphragmatic breathing techniques and pelvic floor activation should be an important part of a core-strengthening program.
For more detailed information on the musculature of the core, as it relates to strength and stability, click here or review the SlideShare presentation above.