Hidetoshi Hirano

Analysis of head movements coupled with trunk drift in healthy subjects

Accelerometers were used to measure sequential head tilt and trunk drift in 14 healthy young subjects while they performed three kinds of head task. First, maximum inclination angles in anterior, posterior, right and left directions were measured to estimate cervical ranges of motion for flexion-extension and lateral bending. The inclination angles measured (61.2° on average for flexion, 51.7° for extension, 42.7° for right bending and 43.9° for left bending) were consistent with previous findings. Secondly, cross-correlation analysis was applied to evaluate the degree of functional coupling between the head and trunk during flexion-extension and lateral bending. Significantly higher correlation coefficients were found between head tilt and trunk drift when these movements were in the same (iso-) directional condition than in a different (allo-) directional condition. The coupled trunk drift in flexion-extension for the iso-directional condition (10.3° on average) was much larger than for the allodirectional condition (2.3°). Finally, head turning was recorded as oval traces in a biaxial plane. In both clockwise and counter-clockwise head turning conditions, the maximum inclination angles of the traces were larger in the anterior-posterior direction (59.8° anterior and 58.2° posterior, in the clockwise condition, and 47.4° and 47.4° in the counter-clockwise condition) than in the right-left direction (36.3° right and 39.0° left, in the clockwise condition, and 40.5° and 36.7° in the counter-clockwise condition), and the angles in the four directions were almost equal to flexion-extension and lateral bending. The characteristics of the traces recorded and a possible application of the present recording system are discussed.