Ice hockey is a high-velocity, collision-heavy sport, increasing players' susceptibility to head impacts and traumatic brain injuries (TBIs). Recent studies emphasize the risk posed by sub-concussive and concussive impacts, particularly in professional leagues, where the intensity of play leads to repeated head traumas. Body-first impacts, such as shoulder-to-glass collisions, contribute to the incidence of TBIs in ice hockey, yet the biomechanical response involving neck stiffness and head kinematics during these impacts remains underexplored.

This study investigates the influence of neck muscle forces on head injuries during body-first impacts, specifically shoulder-to-glass collisions in professional ice hockey. By examining the effects of varying neck stiffness levels and impact velocities, this research aims to enhance biomechanical understanding and inform the development of preventive strategies to mitigate head injury risk.

Twenty professional hockey games from the 2016-2017 season were analyzed using video footage to identify 47 shoulder-first head impacts. Kinovea software quantified impact velocities and categorized them into low, medium, and high ranges for reconstruction. A Hybrid III headform, equipped with an accelerometer array and positioned on the University of Ottawa Neck Spring Apparatus (uONSA), simulated head impacts across three neck stiffness levels and three impact velocities. Maximum voluntary contraction (MVC) values guided the setup of neck stiffness conditions to represent the upper trapezius, splenius capitis, and sternocleidomastoid muscle groups. Each trial involved a high-speed impactor simulating shoulder-first impacts followed by head-to-glass contacts, with three trials per condition.

Twenty-seven shoulder impacts were collected using a fully crossed design, with three impacts at each combination of low, medium, and high neck stiffness and impact velocities of 3, 5, and 7 m/s. High-speed video and kinematic analysis examined dynamic responses during these impacts. Six impacts at 3 m/s with high and medium neck stiffness did not result in a secondary head-to-glass impact, instead displaying a whiplash-like motion. Mean peak linear and rotational accelerations and rotational velocity were calculated for each combination of velocity and neck stiffness, and dynamic response curves were generated. Results indicated that higher neck stiffness reduced linear and rotational acceleration at lower velocities, particularly 3 m/s, suggesting a potential protective effect. However, peak accelerations rose across all neck stiffness levels as impact velocity increased. For example, at 3 m/s, mean linear accelerations were 21.4 g, 10.98 g, and 10.03 g for low, medium, and high stiffness, respectively, while at 7 m/s, they reached 76.13 g, 94.40 g, and 64.30 g, respectively. Rotational accelerations followed a similar trend, with low neck stiffness producing higher values at lower velocities but converging as velocity increased.

A two-way ANOVA revealed significant main effects for neck stiffness and impact velocity on peak linear acceleration (F=25.7, p<​0.001), rotational acceleration (F=30.729, p<​0.001), and rotational velocity (F=152.20, p<​0.001). Post-hoc analyses showed that each level of neck stiffness and impact velocity independently influenced peak accelerations, with significant differences across stiffness levels at various velocities. The study also identified five instances where the highest peak occurred during the head-to-glass impact rather than the shoulder contact. Impact events at lower velocities (3 m/s) with high and medium neck stiffness showed longer durations without secondary impacts, emphasizing that increased neck stiffness can limit head movement in low-velocity impacts. Results aligned with prior research indicating that, while higher neck stiffness can reduce head motion, the effectiveness diminishes as impact velocity increases. For instance, medium stiffness at 7 m/s resulted in rotational acceleration values that approached the threshold associated with an 80% risk of brain injury (7900 rad/s²).

This study's findings underscore the complex interplay between neck stiffness and impact velocity in influencing head kinematics. Although higher neck stiffness may reduce peak accelerations under low-velocity impacts, it may not be sufficient at higher velocities, as shown by instances where rotational accelerations at medium and high stiffness levels approached brain injury thresholds. Limitations include the discrepancy between laboratory simulations and real-world conditions, as the study used a 50th percentile male headform and simplified neck model that may not fully capture human neuromuscular responses. These results contribute to understanding the biomechanical factors in head injury dynamics, supporting the development of targeted interventions to enhance player safety in sports.