Anticipation matters: sex differences in head acceleration responses and implications for sport-related concussion

Introduction
Sport-related concussion (SRC) is a major health concern in contact sports. Linear head acceleration (LHA) and rotational head acceleration (RHA) are central biomechanical markers, and anticipatory neck muscle activation may mitigate these forces. Evidence on how anticipation influences head kinematics, and whether sex differences exist, remains limited. This study compared head acceleration between anticipated and unanticipated perturbations and examined potential sex-specific differences.

Materials and Methods
Thirty physically active adults (15 female, 15 male) completed standardized head perturbations in flexion, extension, lateral flexion, and rotation using a custom-built apparatus. Perturbations were delivered under anticipated (pre-activated neck muscles) and unanticipated (masked, relaxed) conditions. Head kinematics were recorded with 3D motion capture. Mixed ANOVA was used to test effects of sex and condition.

Results
Unanticipated perturbations produced significantly greater accelerations than anticipated perturbations across all directions (LHA mean difference ranged from 0.02 to 0.04 g, p<0.001; RHA mean difference ranged from 1.1 to 4.0 rad/s2, p≤0.053). Females exhibited greater RHA than males, particularly during rotation, with higher values in both anticipated (41.7 vs. 37.3 rad/s2; p=0.003) and unanticipated (42.9 vs. 40.0 rad/s2; p=0.052) conditions. No sex differences were observed for LHA.

Conclusion
Anticipatory neck muscle activation reduced both LHA and RHA, supporting its potential role as a protective mechanism against SRC. Females consistently exhibited higher RHA than males, particularly in rotational trials under both anticipated and unanticipated conditions. These findings point to sex-specific differences in head-neck control and underscore the importance for further research to inform tailored SRC prevention strategies.