Of the three muscles that comprise the erector spinae, the spinales has the greatest lever arm and hence mechanical advantage for causing lateral spinal flexion (sidebending).

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Quizplus · Accepted Answer

The iliocostalis, not the spinales, has the greatest lever arm and hence mechanical advantage for causing lateral spinal flexion due to its lateral and posterior position relative to the spine.

Of the Three Muscles That Comprise the Erector Spinae, the Spinales