Anne-Louise Haas, Katrin Bracht, Thomas Stöggl and Reinald Brunner
Background and Purpose: It is generally assumed that the head is positioned on the body plumb line. The reference line defined by Kendall (KL) (1952, Kendall et al. 2005) is the most citied one. We hypothesized that the head is held anteriorly to the KL and the gravity line (GL) derived from the center of mass (CoM). The purpose of the study was to objectively assess the relation between head position and GL / KL in the sagittal plane using a 3d-tool to define the CoM. Methods: Head center (HC) and CoM were calculated in 30 normal subjects (25-35 years) while standing using a three dimensional motion analysis system. The distance from the GL (defined by the CoM) and KL (two cm in front of the lateral malleolus) to the HC was calculated. Results: All 30 subjects held their HC anterior to the KL. The HC was anterior to the GL in 11 subjects, through the GL in four and posterior to the GL in 15. Conclusion: According to this study the two references lines cannot be considered the same, suggesting that previous assumptions about this relationship may be inaccurate. KL was not discriminative in our subjects for HC position.
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