Aim

The purpose of this study was to evaluate the variation in natural head position (NHP) over five minutes using an inertial measurement unit (IMU).

Material and methods

Fifteen healthy young volunteers were asked to sit on a chair and keep their head in the self-balanced position for five minutes. A mirror was then revealed in front of them, and they were asked to look at their eyes for 20 seconds. This procedure was undertaken on two separate occasions with a one-week interval. This was compared to an instantaneous measurement of head position at a specific time point corresponding to the 15th second of the recording.

Results

During the five minutes of recording, the participants tended to elevate their head progressively by a mean of 1.5°, which is then corrected by looking at oneself in the mirror. Most participants tended to rotate their head to the left and continued that progressive rotation despite looking in the mirror. The roll axis had no systematic changes observed between the self-balanced position and the mirror-guided position and was the most reproducible axis. Moderate to good correlations were found comparing both sessions for each axis.

Conclusion

The comparison between the five-minute analysis and the instantaneous measurement showed a systematic difference on the pitch axis but no differences for the yaw and roll. These results suggest that the variation in NHP during a period of five minutes is generally specific to each participant with a head elevation and rotation to the left in most cases.