The effect of isometric cervical strength, head impact location, and impact mechanism on simulated head impact measures in female ice hockey players

Abstract

Head injuries in sport have become a growing concern due to the negative acute and chronic health effects manifested from concussion injuries. Ice hockey is a sport associated with a high rate of concussions, although most research has focused on concussions in men’s hockey. Comparatively, women’s hockey has not only seen a drastic increase in participation rates, but female hockey players also exhibit a higher concussion rate than male players, despite the “no body contact” rule that is founding characteristic of women’s hockey. In fact, female hockey players may be more at risk for concussions than their male counterparts. The concerning prevalence of concussions in women’s hockey has been identified, yet the factors contributing to the high risk of concussions are still unclear. Among others, factors such as cervical muscle strength, head impact location, and impact mechanism have all been discussed in the literature as potential variables influencing the risk of concussion in athletes. The influence of these factors on head impact biomechanics, however, have not been thoroughly investigated. Furthermore, women experience high rates of concussion that have been potentially linked to decreased cervical muscle strength; however, there is little research that has characterized cervical muscle strength among female hockey players and limited research that has developed a set of normative data for female hockey players. Consequently, the purpose of this study was twofold. The first purpose was to develop normative data on the isometric cervical muscle strength and anthropometrics of female hockey players. The second purpose was to examine the effect of neckform torque, head impact location, and impact mechanism on simulated head impact measures of peak linear acceleration, shear force, and injury risk in female hockey players. To address the first purpose, the isometric cervical strength of a sample of female hockey players (n= 25) was measured in flexion, extension, and side flexion. An average of the muscle strength in these three directions was then calculated to develop an average overall isometric cervical strength measure for each athlete. Overall cervical strength measures of 58.64 N, 76.01 N, and 108.27 N (SD=17.52 N) represented the 10th, 50th, and 90th percentiles, respectively, of the normally distributed dataset created from the sample. These measures were then scaled and transformed into torque measures to be appropriately modelled on a mechanical neckform to address Part II of the simulation study. The 10th, 50th, and 90th percentile isometric cervical strength measures corresponded to torque measures of 1.36 Nm (weak), 2.94 Nm (average), and 4.62 Nm (strong), respectively, as established through calibration and transformation of the data. To address the second purpose, three neckform torques (weak, average, and strong), three helmet impact locations (front, rear, and side), and two impact mechanisms (direct and whiplash+impact) were tested at 16 different drop speeds using a dual-rail vertical drop system. The outcome measures included peak linear acceleration, shear force, and Gadd Severity Index, as these are variables commonly used to assess concussions in athletes.