A review of the literature related to trunk muscle performance.

In the past, there has been no comprehensive review of the literature pertaining to different methods of assessing trunk muscle strength. This review describes the different studies that have been performed, and determines the hierarchy of strength values and agonist/antagonist strength ratios for the trunk musculature. In general, the strength hierarchy consists of, from strongest to weakest: extension, flexion, side bending, and rotation. The agonist/antagonist ratio for extension/flexion is 1.30 and for rotation and side bending, motion to the right approximately equals motion to the left. Changes in the relative strengths of the different trunk muscle groups is affected by spinal pathology, and this is discussed. Possible clinical implications and direction for future research are delineated based on the findings of this review.