Kinematics of head movement in simulated low velocity rear-end impacts

Objectives. To evaluate kinematics of head movement related to impact velocity, gender and awareness in simulated low velocity rear-end impacts. Methods. Thirty individuals were subjected in random order to three rear-end impacts: two unexpected impacts causing chair acceleration of 4.5 m/s(2) (slow) and 10. 0 m/s(2) (fast) and one 10.0 m/s(2) expected impact. Rearward head displacement, and linear and angular head accelerations were recorded. Results. Angular head displacement was almost two times higher for the fast than the slow unexpected-impacts (P = 0.04). Rearward and forward angular head accelerations increased two to three times with increased impact magnitude (P < 0.05). Rearward and forward linear head accelerations were two and a half to three and a half times higher for the fast than for the slow unexpected impacts (P < 0.05). Males presented two times higher upward linear head acceleration than females in the unexpected fast impact. No significant magnitude differences were identified for impact awareness in kinematics of head movement (P > 0.05). Rearward angular head acceleration reached the peak between 62 and 84 ms later than the rearward linear head acceleration (P < 0.05) in all impacts. No significant differences were identified for timing of kinematics of head movement (P > 0.05) with increased impact magnitude; however, statistical powers were low. I nterpretation. Kinematics of head movement increases with increased impact magnitude. Gender differences exist for vertical linear head acceleration only. Temporal and amplitude awareness do not change the magnitude in kinematics of head movement. There are temporal differences between angular and linear head accelerations. (c) 2005 Elsevier Ltd. All rights reserved.