Abdominal strength exercises such all types of crunches are popular both in the general public and with those involve in rehabilitation.
The reasons for this popularity is appearance of a flat stomach and the assumption that a strong abdomen protects the spine.
Often, programs designed to strengthen abdominal muscles will contribute to muscle imbalances and pain syndromes.
The most important aspect of abdominal muscles performance is obtaining the control that is necessary to appropriately stabilize the spine, maintain optimal alignment and movement relationships between the pelvis and spine, and prevent excessive stress and compensatory motions of the pelvis during movement of the extremities.
In fact, Cholewicki and others report that only 2% to 3% of maximum voluntary activity of the abdominal muscles is necessary for stabilizing the spine during upright unloaded tasks. In sport performance the abdominal muscles are also helping us explode while decelerate and prevent unwanted movement and leaks of energy. At the same time some muscles contract concentrically to produce force while others contract eccentrically to decelerate and stabilize and prevent unneeded movement.
From this we understand that the selection and instruction of abdominal exercises has to be based not only on strength but the control that is needed and in the case of back pain the type of stresses that contribute to pain.
The most important factors that need attention are sequence of activation, with the deeper, smaller, stabilizing muscles firing before the big prime movers and maintaining balance development between abdominal and back muscles, flexors and extensors.
Because of misunderstanding many people perform various forms of crunches which cause the rectus abdominis to become dominant over the oblique’s external and internal.
Study shows that there is greater rectus activation during sit up (68%) comparing to external oblique (19%) and internal oblique (14%).
The disadvantage of this is that the rectus abdominis cannot produce or decelerate rotation which is most important in most life tasks and sports and shortness or stiffness contribute to thoracic kyphosis.
Also during sit up there is strong activity of the iliopsoas, and in the case of a person with back pain when the source is compression and anterior shear, which is what the iliopsoas are causing, the activation of this muscle should be minimized.
The best way to train the abdominal muscles is through functional whole body movements, strengthening the abdominals while it cooperate with the whole kinetic chain.
Some isolation exercises are useful when certain muscles are dormant or delayed in recruitment, in particular the inner unit, the deeper stabilizing muscles, closer to the spine.
Also in the common case of slouched posture, strengthening the back extensors is necessary.
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