Verschiedene Kenngrößen für die physiologisch günstige Kopfneigung

ZusammenfassungDas Sehen am Bildschirm erfordert die abgestimmte Bewegungskoordination der Augen und des Kopfes. Dabei kann die eingenommene Kopfneigung von Bedeutung sein. Diese Studie untersucht horizontale Kopfb ewegungen mithilfe des Trackingverhaltens und weiterer Indikatoren für eine physiologisch günstige Kopfneigung. Die komfortable Kopfneigung, die Probanden spontan in einem Schnelltest selbst einstellen, war korreliert mit zwei weiteren Indikatoren: erstens mit der Kopfneigung, bei der die subjektiv beurteilte Nackenanstrengung minimal war, und zweitens mit der Ruhe-Kopfneigung, auf die sich der Kopf vertikal hinbewegt, wenn der Proband horizontale Kopfb ewegungen mit geschlossenen Augen ausführt. Einige Indikatoren, darunter das Elektromyogramm des Musculus Sternocleidomastoideus und die subjektive Beurteilung von Nackenbeschwerden, zeigten einen ähnlichen Beanspruchungsverlauf als Funktion der vorgegebenen Kopfneigung. Die Bestimmung der komfortablen Kopfneigung und der dazugehörigen komfortablen Blickneigung erscheint als ein einfaches und praxisgerechtes Verfahren, das als Anhaltspunkt für die individuelle Optimierung der vertikalen Bildschirmposition nützlich sein kann.AbstractA physiologically favourable head tilt should be adopted at computer work by an ergonomic optimization of the vertical monitor position, in order to reduce musculoskeletal complaints. The aim of this study was to investigate head movements during a horizontal head-tracking task and further indicators for a physiologically favourable head inclination.First, to find the comfortable head tilt, subjects performed small horizontal head movements with closed eyes in different vertical head positions until they found their individual favorable head tilt. Then, a head-mouse system — designed for computer interaction — was used in a way that subjects performed horizontal head movements to keep a cursor (vertical line) on a target (rectangle) which moved with variable velocity on a 44° wide screen. This was repeated with head tilts of -20°, -10°, 0°, +10°, +20° (Frankfurt line relative to horizontal) and the comfortable head tilt, while the activity of the musculus sternocleidomastoideus was measured by electromyography. For each head tilt, subjects judged the magnitude of perceived neck strain during tracking. The horizontal precision and the vertical deviation of the target position during tracking were measured as a function of head tilt. Further, we measured the resting position of head tilt, defined as the head tilt towards which the head tends to move vertically when performing horizontal head movements with closed eyes.The results in 16 participants showed a linear increase in tracking precision the more the head was inclined upwards, but this effect was negligible. Other indicators suggested a favorable condition more or less near a 0° Frankfurt line, specifically a U-shaped function was found for the EMG activity of the musculus sternocleidomastoideus and the subjective judgment of strain in the neck.Three indicators had significant test-retest- correlations (r > 0.5, p < 0.05) and showed the following inter-correlations: the comfortable head tilt (+5.1 ± 4.2°) was significantly correlated to the resting head tilt with horizontal head movements (+4.5 ± 8.9°, r = 0.58, p = 0.0093; boThmeasures used closed eyes to eliminate external stimuli) and to the head tilt of subjectively minimal strain when observing the visual head tracking targets (-1.6 ± 9.4°, r = 0.50, p = 0.0243); these means and standard deviations refer to Session 2 and the Frankfurt line relative to horizontal; the eye-ear-line is about 11° higher. For practical purposes, the comfortable head tilt and the comfortable gaze inclination can easily be tested at the workplace as starting value to determine the individually favorable vertical monitor position to improve subjective neck comfort and to avoid musculoskeletal strain in the neck.