Figure 1. Muscles of the Abdomen<\/strong><\/p>\n\n\n\n (a) The anterior abdominal muscles include the medially located rectus abdominis, which is covered by a sheet of connective tissue called the rectus sheath. On the flanks of the body, medial to the rectus abdominis, the abdominal wall is composed of three layers. The external oblique muscles form the superficial layer, while the internal oblique muscles form the middle layer, and the transverses abdominus form the deepest layer. (b) The muscles of the lower back move the lumbar spine but also assist in femur movements.<\/p>\n\n\n\n There are three flat skeletal muscles in the anterolateral wall of the abdomen. The\u00a0external oblique, closest to the surface, extends inferiorly and medially, in the direction of sliding one\u2019s four fingers into pants pockets. Perpendicular to it is the intermediate\u00a0internal oblique<\/strong>, extending superiorly and medially, the direction the thumbs usually go when the other fingers are in the pants pocket. The deep muscle, the\u00a0transversus abdominis<\/strong>, is arranged transversely around the abdomen, similar to the front of a belt on a pair of pants. This arrangement of three bands of muscles in different orientations allows various movements and rotations of the trunk. The three layers of muscle also help to protect the internal abdominal organs in an area where there is no bone.<\/p>\n\n\n\n The\u00a0linea alba<\/strong>\u00a0is a white, fibrous band that is made of the bilateral\u00a0rectus sheaths\u00a0<\/strong>that join at the anterior midline of the body. These enclose the\u00a0rectus abdominis\u00a0<\/strong>muscles (a pair of long, linear muscles, commonly called the \u201csit-up\u201d muscles) that originate at the pubic crest and symphysis, and extend the length of the body\u2019s trunk. Each muscle is segmented by three transverse bands of collagen fibers called the\u00a0tendinous intersections<\/strong>. This results in the look of \u201csix-pack abs,\u201d as each segment hypertrophies on individuals at the gym who do many sit-ups.<\/p>\n\n\n\n The posterior abdominal wall is formed by the lumbar vertebrae, parts of the ilia of the hip bones, psoas major and iliacus muscles, and\u00a0quadratus lumborum<\/strong>\u00a0muscle. This part of the core plays a key role in stabilizing the rest of the body and maintaining posture.<\/p>\n\n\n\n Career Connections<\/span><\/p>\n\n\n\n Physical Therapists<\/strong><\/p>\n\n\n\n Those who have a muscle or joint injury will most likely be sent to a physical therapist (PT) after seeing their regular doctor. PTs have a master\u2019s degree or doctorate and are highly trained experts in the mechanics of body movements. Many PTs also specialize in sports injuries.<\/p>\n\n\n\n If you injured your shoulder while you were kayaking, the first thing a physical therapist would do during your first visit is to assess the functionality of the joint. The range of motion of a particular joint refers to the normal movements the joint performs. The PT will ask you to abduct and adduct, circumduct, flex, and extend the arm. The PT will note the shoulder\u2019s degree of function, and based on the assessment of the injury, will create an appropriate physical therapy plan.<\/p>\n\n\n\n The first step in physical therapy will probably be applying a heat pack to the injured site, which acts much like a warm-up to draw blood to the area, to enhance healing. You will be instructed to do a series of exercises to continue the therapy at home, followed by icing, to decrease inflammation and swelling, which will continue for several weeks. When physical therapy is complete, the PT will do an exit exam and send a detailed report on the improved range of motion and return of normal limb function to your doctor. Gradually, as the injury heals, the shoulder will begin to function correctly. A PT works closely with patients to help them get back to their normal level of physical activity.<\/p>\n\n\n\n The muscles of the chest serve to facilitate breathing by changing the size of the thoracic cavity (Table 7). When you inhale, your chest rises because the cavity expands. Alternately, when you exhale, your chest falls because the thoracic cavity decreases in size.<\/p>\n\n\n\n The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the\u00a0diaphragm\u00a0(Figure 2). It separates the thoracic and abdominal cavities and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.<\/p>\n\n\n Figure 2. Muscles of the Diaphragm<\/strong><\/p>\n\n\n\n The diaphragm separates the thoracic and abdominal cavities.<\/p>\n\n\n\n Defecating, urination, and even childbirth involve cooperation between the diaphragm and abdominal muscles (this cooperation is referred to as the \u201cValsalva maneuver\u201d). You hold your breath with a steady contraction of the diaphragm; this stabilizes the volume and pressure of the peritoneal cavity. When the abdominal muscles contract, the pressure cannot push the diaphragm up, so it increases pressure on the intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).<\/p>\n\n\n\n The inferior surface of the pericardial sac and the inferior surfaces of the pleural membranes (parietal pleura) fuse onto the central tendon of the diaphragm. To the sides of the tendon are the skeletal muscle portions of the diaphragm, which insert into the tendon while having several origins including the xiphoid process of the sternum anteriorly, the inferior six ribs and their cartilages laterally, and the lumbar vertebrae and 12th ribs posteriorly.<\/p>\n\n\n\n The diaphragm also includes three openings for the passage of structures between the thorax and the abdomen. The inferior vena cava passes through the\u00a0caval opening<\/strong>, and the esophagus and attached nerves pass through the esophageal hiatus. The aorta, thoracic duct, and azygous vein pass through the aortic hiatus of the posterior diaphragm.<\/p>\n\n\n\n There are three sets of muscles, called\u00a0intercostal muscles, which span each of the intercostal spaces. The principal role of the intercostal muscles is to assist in breathing by changing the dimensions of the rib cage<\/strong>\u00a0(Figure 3).<\/p>\n\n\n Figure 3. Intercostal Muscles<\/strong><\/p>\n\n\n\n The external intercostals are located laterally on the sides of the body. The internal intercostals are located medially near the sternum. The innermost intercostals are located deep into both the internal and external intercostals.<\/p>\n\n\n\n The 11 pairs of superficial\u00a0external intercostal\u00a0muscles aid in the inspiration of air during breathing because when they contract, they raise the rib cage, which expands it. The 11 pairs of\u00a0internal intercostal<\/strong>\u00a0muscles, just under the externals, are used for expiration because they draw the ribs together to constrict the rib cage. The\u00a0innermost intercostal<\/strong>\u00a0muscles are the deepest, and they act as synergists for the action of the internal intercostals.<\/p>\n\n\n\n The pelvic floor is a muscular sheet that defines the inferior portion of the pelvic cavity. The\u00a0pelvic diaphragm<\/strong>, spanning anteriorly to posteriorly from the pubis to the coccyx, comprises the levator ani and the ischiococcygeus. Its openings include the anal canal and urethra, and the vagina in women.<\/p>\n\n\n\n The large\u00a0levator ani\u00a0consists of two skeletal muscles, the\u00a0pubococcygeus<\/strong>\u00a0and the\u00a0iliococcygeus<\/strong>\u00a0(Figure 4). The levator ani is considered the most important muscle of the pelvic floor because it supports the pelvic viscera. It resists the pressure produced by contraction of the abdominal muscles so that the pressure is applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted by the\u00a0ischiococcygeus<\/strong>, which pulls the coccyx anteriorly). This muscle also creates skeletal muscle sphincters at the urethra and anus.<\/p>\n\n\n Figure 4. Muscles of the Pelvic Floor<\/strong><\/p>\n\n\n\n The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.<\/p>\n\n\n\n The\u00a0perineum\u00a0<\/strong>is the diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus). Divided transversely into triangles, the anterior is the\u00a0urogenital triangle<\/strong>, which includes the external genitals. The posterior is the\u00a0anal triangle<\/strong>, which contains the anus (Figure 5). The perineum is also divided into superficial and deep layers with some of the muscles common to men and women (Figure 6). Women also have the\u00a0compressor urethrae<\/strong>\u00a0and the\u00a0sphincter urethrovaginalis<\/strong>, which function to close the vagina. In men, there is the\u00a0deep transverse perineal<\/strong>\u00a0muscle that plays a role in ejaculation.<\/p>\n\n\n Figure 5. Muscles of the Perineum<\/strong><\/p>\n\n\n\n The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women.<\/p>\n\n\n Figure 6. Muscles of the Perineum Common to Men and Women<\/strong><\/p>\n\n\n\n Made of skin, fascia, and four pairs of muscles, the anterior abdominal wall protects the organs located in the abdomen and moves the vertebral column. These muscles include the rectus abdominis, which extends through the entire length of the trunk, the external oblique, the internal oblique, and the transversus abdominus. The quadratus lumborum forms the posterior abdominal wall.<\/p>\n\n\n\n The muscles of the thorax play a large role in breathing, especially the dome-shaped diaphragm. When it contracts and flattens, the volume inside the pleural cavities increases, which decreases the pressure within them. As a result, air will flow into the lungs. The external and internal intercostal muscles span the space between the ribs and help change the shape of the rib cage and the volume-pressure ratio inside the pleural cavities during inspiration and expiration.<\/p>\n\n\n\n The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women. The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.<\/p>\n\n\n\n anal triangle<\/strong><\/p>\n\n\n\n posterior triangle of the perineum that includes the anus<\/p>\n\n\n\n caval opening<\/strong><\/p>\n\n\n\n opening in the diaphragm that allows the inferior vena cava to pass through; foramen for the vena cava<\/p>\n\n\n\n compressor urethrae<\/strong><\/p>\n\n\n\n deep perineal muscle in women<\/p>\n\n\n\n deep transverse perineal<\/strong><\/p>\n\n\n\n deep perineal muscle in men<\/p>\n\n\n\n diaphragm<\/strong><\/p>\n\n\n\n skeletal muscle that separates the thoracic and abdominal cavities and is dome-shaped at rest<\/p>\n\n\n\n external intercostal<\/strong><\/p>\n\n\n\n superficial intercostal muscles that raise the rib cage<\/p>\n\n\n\n external oblique<\/strong><\/p>\n\n\n\n superficial abdominal muscle with fascicles that extend inferiorly and medially<\/p>\n\n\n\n iliococcygeus<\/strong><\/p>\n\n\n\n the muscle that makes up the levator ani along with the pubococcygeus<\/p>\n\n\n\n innermost intercostal<\/strong><\/p>\n\n\n\n the deepest intercostal muscles that draw the ribs together<\/p>\n\n\n\n intercostal muscles<\/strong><\/p>\n\n\n\n muscles that span the spaces between the ribs<\/p>\n\n\n\n internal intercostal<\/strong><\/p>\n\n\n\n muscles the intermediate intercostal muscles that draw the ribs together<\/p>\n\n\n\n internal oblique<\/strong><\/p>\n\n\n\n flat, intermediate abdominal muscle with fascicles that run perpendicular to those of the external oblique<\/p>\n\n\n\n ischiococcygeus<\/strong><\/p>\n\n\n\n muscle that assists the levator ani and pulls the coccyx anteriorly<\/p>\n\n\n\n levator ani<\/strong><\/p>\n\n\n\n pelvic muscle that resists intra-abdominal pressure and supports the pelvic viscera<\/p>\n\n\n\n linea alba<\/strong><\/p>\n\n\n\n white, fibrous band that runs along the midline of the trunk<\/p>\n\n\n\n pelvic diaphragm<\/strong><\/p>\n\n\n\n the muscular sheet that comprises the levator ani and the ischiococcygeus<\/p>\n\n\n\n perineum<\/strong><\/p>\n\n\n\n the diamond-shaped region between the pubic symphysis, coccyx, and ischial tuberosities<\/p>\n\n\n\n pubococcygeus<\/strong><\/p>\n\n\n\n the muscle that makes up the levator ani along with the iliococcygeus<\/p>\n\n\n\n quadratus lumborum<\/strong><\/p>\n\n\n\n posterior part of the abdominal wall that helps with posture and stabilization of the body<\/p>\n\n\n\n rectus abdominis<\/strong><\/p>\n\n\n\n long, linear muscle that extends along the middle of the trunk<\/p>\n\n\n\n rectus sheaths<\/strong><\/p>\n\n\n\n tissue that makes up the linea alba<\/p>\n\n\n\n sphincter urethrovaginalis<\/strong><\/p>\n\n\n\n deep perineal muscle in women<\/p>\n\n\n\n tendinous intersections<\/strong><\/p>\n\n\n\n three transverse bands of collagen fibers that divide the rectus abdominis into segments<\/p>\n\n\n\n transversus abdominis<\/strong><\/p>\n\n\n\n deep layer of the abdomen that has fascicles arranged transversely around the abdomen<\/p>\n\n\n\n urogenital triangle<\/strong><\/p>\n\n\n\n anterior triangle of the perineum that includes the external genitals Training your abdominal muscles with constant tension is a quick way to strengthen and tone your midsection. For a great stability and core workout, try the wood chop exercise.\u00a0Muscles of the Thorax<\/h2>\n\n\n\n
The Diaphragm<\/h2>\n\n\n\n
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The Intercostal Muscles<\/h2>\n\n\n\n
Muscles of the Pelvic Floor and Perineum<\/h2>\n\n\n\n
REVIEW<\/h2>\n\n\n\n
GLOSSARY<\/h2>\n\n\n\n
<\/p>\n\n\n\nBodyFly Abs\/Core Exercises<\/h2>\n\n\n\n
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