The reliability of isometric neck strength assessments in trained individuals

Cervical muscle strength has been identified as a modifiable risk factor for concussion and cervical spine injury. At present, there is a dearth of research investigating reliable methods of measuring neck strength which are: suitable for implementation into a sporting environment (for example: a strength and conditioning suite, training facility and match facility), accessible to athletes who play contact sport or are at risk of suffering concussion, and which can be used for regular testing, monitoring and evaluation of groups of athletes. The aim of this investigation was to examine the reliability of a method of measuring isometric neck strength using a portable dynamometer (PD) mounted on a custom-built bracket, appropriate for use in an applied sport and exercise environment. Measurements were conducted in flexion, right-side flexion, extension, and left-side flexion using a PD and custom-built rack. Fourteen participants had their isometric neck strength measured in two sessions, 24 h apart at a university strength and conditioning gym. Participants completed three isometric contractions in each of the four directions with 30 s between each repetition. Participants peak isometric neck strength measurements and time to peak force measurements were used for data analysis. The height of the PD and order of pushing positions remained constant between both sessions. This method demonstrated strong relative and absolute reproducibility for measuring peak isometric force (PF) of the neck musculature in all directions (PF ICC ranged between 0.78 - 0.94 across all directions. PF r ranged between 0.81 - 0.92 across all directions. PF CV% ranged between 8.86 - 10.43 in all directions). However, findings show poor relative reproducibility for the measurement of time to peak isometric force (TPF). Systematic bias was small and the difference between the trials for PF and TPF were not significant (p > 0.05 in all directions).