Precision and Test-Retest Reliability of Self-Assessed Neck Strength in UK Youth Rugby Using a Novel Test Protocol and Fixation Device

Introduction
Neck strength has been proposed as an important concussion risk mitigator, especially in sports with frequent high-impact collisions. While monitoring of neck strength could prove essential for injury prevention and rehabilitation, access to equipment and trained personnel is often limited in non-elite settings. A cost-effective solution for reliable self-assessments could help close the gap between elite and amateur athletes. The aim of this study was therefore to develop and assess the reliability and precision of a self-assessed neck strength test protocol.

Materials and Methods
Twenty youth rugby players (age: 14-22 years, mean: 16.2±1.8 years) participated. A custom 3D-printed fixation device was used to mount the ActivForce2 dynamometer on a rugby post for secure, self-assessed testing. Participants assessed neck strength in flexion, extension, and lateral flexion on three occasions (twice on day one, once on day two). Each performed three maximal isometric contractions with 30-second rests between repetitions. Reliability was measured using Intraclass Correlation Coefficients (ICCs), and precision was evaluated using Standard Error of Measurement and Minimum Detectable Change.

Results
Both within- and between-day reliability was excellent. Within-day ICCs ranged from 0.944 to 0.982, and between-day ICCs ranged from 0.961 to 0.971 across all movements (p<0.0001). Standard Error of Measurements ranged from 9.6 to 16.7 N, and Minimum Detectable Change varied from 26.7 to 46.2 N across all movements.

Conclusion
The self-assessed neck strength test protocol, utilising a 3D-printed fixation device and handheld dynamometer, offers a precise, reliable, and cost-effective solution for easy neck strength assessments, well-suited for longitudinal monitoring.