It’s About the Posture, Not the Core
94 E5649/Brewer/fig 05.13a/542793/pulled/R
Internal oblique Rectus abdominis Transversus abdominis E5649/Brewer/fig 05.13b/542794/pulled/R1 Gluteus minimus Gluteus medius (cut) Multifidus Erector spinae: Spinalis Longissimus Iliocostalis Quadratus lumborum Gluteus maximus Psoas major Iliopsoas: Adductor longus Vastus intermedius Adductor magnus Adductor brevis Sartorius Tensor fasciae latae Pectineus Gracilis Rectus femoris Quadriceps femoris: Vastus lateralis Vastus medialis Tibialis anterior E5649/Brewer/fig 05.13d/542795/pulled/mh-R2 Iliacus E5649/Brewer/fig 05.13e/542796/pulled/mh-R2 Gemellus superior Obturator internus Gemellus inferior Quadratus femoris Piriformis Gluteus minimus Gluteus medius Gluteus maximus Adductor magnus Iliotibial tract Biceps femoris Hamstrings: Semi- tendinosus Semi- membranosus Gastrocnemius E5649/Brewer/fig 05.13c/548501/pulled/R1 Psoas major Iliopsoas: Psoas minor Iliacus
Figure 5.13 Posture and power muscles in the
Table 5.2 Power and Postural Muscles in the Midsection
Muscle Major function
Transversus abdominis Deepest of the three lateral abdominal muscles. Compresses the abdominal wall, aiding in the stabilization of the abdominal tissue and in the action of the other trunk muscles. Especially important in forced expiration (bracing).
Internal oblique If activated bilaterally (on both sides of the trunk), this muscle flexes the vertebral column, tilting the pelvis anteriorly and bringing it closer to the trunk. If activated unilaterally, the muscle acts with the external oblique to flex the spine laterally and rotate the vertebral column.
External oblique Acting bilaterally, this muscle flexes the lumbar spine, tilting the pelvis posteriorly. If activated unilaterally in conjunction with the internal oblique, this muscle causes side (lateral) flexion of the trunk. Also involved in the rotation of the vertebral column. Multifidus Extends the vertebral column and rotates it towards the opposite side.
Gluteus medius Abducts the femur at the hip and medially rotates the thigh, thus assisting in
stabilization of the knee in extension. In locomotion, co-acts with the gluteus minimus to maintain the level position of the pelvis so that the leg can swing forward, not across the body. May also assist in flexion and extension of the hip.
Gluteus minimus Abducts the hip joint and medially rotates the thigh. It may also assist in hip flexion. Rectus abdominis Flexes the spine (i.e., bends the vertebral column forward). If the pelvis is fixed, the
trunk moves forward; if the trunk is fixed, the pelvis moves towards the trunk. Also important in compressing the abdomen.
Erector spinae Composed of three muscles: iliocostalis, longissimus and spinalis. They extend the lumbar and lower thoracic spine, assist in lateral flexion of the spine and rotate the spine for forceful inspiration.
Iliopsoas (psoas major and iliacus)
When the trunk or pelvis is fixed, it flexes the hip joint by bringing the femur (thigh bone) towards the trunk (e.g., swinging the leg forward in walking). Also assists in the lateral rotation and abduction of the hip joint. When the thigh is fixed, it flexes the trunk by bringing it towards the femur. Bilateral action in this situation increases lordosis in the lumbar spine; unilateral action assists in lateral flexion of the trunk to the same side. Rectus femoris Extends the knee as part of the quadriceps femoris group that also includes the vastus
lateralis, vastus medialis and vastus intermedius. Rectus femoris flexes the hip joint by raising the femur towards the trunk.
Sartorius Flexes, laterally rotates and abducts the thigh at the hip joint and aids in the flexion and medial rotation of the knee after flexion. This muscle swings the leg forward in the unsupported phases of running and walking.
Gluteus maximus Typically used only in forceful extension and lateral rotation of the hip joint and stabilization of the knee joint in extension.
Biceps femoris One of three muscles that make up the hamstring group. Flexes and laterally rotates the knee. The long head has a function in extending the hip. Assists in the lateral rotation of the hip. During locomotion, the hamstrings decelerate the forward swing phase of the thigh and prevent trunk flexion at the hip.
Semitendinosus and semimembranosus
With the biceps femoris, make up the hamstring group. Flex and medially rotate the knee, extend the thigh at the hip and assist in the medial rotation of the hip.
through either flexion or extension of the trunk (rectus abdominis or erector spinae) or the hip (rectus femoris and iliopsoas or glu- teus maximus and hamstrings, respectively).
In sport contexts, these movements often are accompanied by rotational or lateral actions, so the associated muscular involvements become more complex. But the basic premise needs to
remain—the postural muscles need to be able to co-act to provide a stable platform from which the power-producing muscles can mobi- lize joints and develop and express large forces. Optimal movement performance relies on this stability and mobility. If either muscle group is producing compensatory movements, the athlete will be compromised and the mus- culature around the lumbar–pelvic area will have to compensate in some ways.
A common example can be seen in teenage athletes who are performing high-intensity running intervals. As fatigue sets in, the athlete may complain of pain in the lower back. Often this occurs because the athlete has compen- sated by using the rectus abdominis to maintain pelvic position. When the athlete reaches the point at which the rectus abdominis becomes involved in other actions (such assisting in breathing at high intensities) and can no longer maintain the pelvic position, the pelvis begins to tilt in an anterior–posterior movement. This tilt decreases movement efficiency and causes pain in the lumbar spine.
Other common movement compensations are seen around the hip; the athlete overuses the hip flexors and quadriceps to perform actions and consequently underuses the gluteal muscles. Often, imbalances and reduced mobil- ity around the hip are the result. A chronic problem develops over time as the move- ment pattern becomes habit, and the muscle imbalance and loss of mobility worsen unless addressed. Although experience shows that the better the athlete’s performance level is, the better he or she is at achieving movement compensations, this situation is not ideal and almost always leads to further complications down the line.
The correct movement mechanics are facil- itated by the ability to produce forces through a full range of mobility from a stable platform. Incorrect mechanics lead to poor mobility, poor stability and inefficiency (increased energy cost for the same amount of work), all of which negatively affect the athlete’s performance capabilities.
Injuries are also an important consideration in the alignment of joints as the athlete moves. As figure 5.8 shows, typically the hips are level
during standing and the knees are in line with the toes. This positioning is also important during movement. As table 5.3 shows, the knee is a hinge joint; it is designed to flex and extend but not to rotate to any significant degree. Indeed, the ligament structures around the knee are specifically designed to allow movement only in the sagittal plane. Frontal plane movement is potentially damaging to the medial and lateral collateral ligaments, and transverse plane movement can cause damage to the anterior and posterior cruciate ligaments.
Because the knee is a complex articulation of the femur (thigh bone) and the tibia (major shin bone), any rotational or lateral movement that occurs here (without considering a direct blow from an external source) is largely the result of movement at either the hip joint (misalignment of the femur) or the ankle (mis- alignment of the tibia). This rotational or lateral movement can have catastrophic consequences for an athlete, because large forces that occur through an inappropriate plane can lead to shear forces, which can compromise some or all of the structures within the knee joint.