Abstract
Background: Women’s football has rapidly professionalised, bringing significant growth and progress to the sport. However, this rapid expansion has often required the adoption of training and player welfare strategies from the men’s game due to insufficient research into female-specific approaches. Female football players experience higher concussion rates and have been shown to experience greater angular acceleration of the head at a given ball velocity in lab-based heading studies. Additionally, research suggests that females also experience more body-to-body impacts in competitive matches. These previous findings point to potential differences in head control mechanisms and playing style, which may contribute to the observed sex disparity in head and neck injuries in football. However, there is limited research on the physiological, neuromechanical, and biomechanical factors contributing to these differences, highlighting the need for further investigation that would help inform targeted injury prevention strategies in the future.
Aims: There were three main aims of this thesis: (1) to investigate if a sex difference in the inertial perturbation response of the head and neck exists during predictable and unpredictable side-on impacts, (2) to explore if sex differences in neck strength characteristics such as Peak Isometric Neck Strength (PINS), Rate of Force Development (RFD) and Electromechanical Delay (EMD) exist and, (3) to investigate what relationship exists between neck strength characteristics (PINS, RFD, and EMD) and the head kinematics experienced during a perturbation.
Methods: Fifty football players (25 male, 25 female) were recruited and screened for eligibility based on concussion and injury history. Anthropometric data and neck measurements were collected. Maximal isometric neck strength was assessed in four directions (extension, flexion, left lateral flexion, and right lateral flexion) using a custom-built device. Head acceleration was examined over a series of predictable and unpredictable inertial head perturbations. The perturbation protocol involved a weighted pendulum arm (15% of the participant's body weight) that impacted the participant's left lateral shoulder under predictable (full sensory availability) and unpredictable (visual and auditory occlusion) conditions. Surface Electromyography (sEMG) measured muscle activity, which was processed using MATLAB, while 2D kinematic head models derived angular accelerations from video analysis using Kinovea. Statistical analyses included mixed models and post-hoc tests to evaluate the effects of sex, neck strength characteristics, and perturbation conditions on head acceleration.
Results: Results of this study identified significant sex-based differences in physical characteristics, strength, and rate-of-force development capabilities that may influence head acceleration and displacement during a perturbation. Males were older, taller, heavier, and had more playing experience compared to females (all p <0.001). Males also produced higher relative peak force in all directions (e.g., extension: p <0.001) and faster rates of force development (RFD), particularly in the extension direction (P <0.05). Females experienced greater head acceleration (p <0.012) and displacement (p=0.021) under unpredictable conditions. Both sexes experienced greater head acceleration in the unpredictable condition compared to the predictable condition (P < 0.05), with a larger difference observed in the female group. Additionally, females demonstrated a stronger relationship between early rate of force development (0-150ms) and head acceleration (P<0.05). No significant sex-based differences were found in electromechanical delay across muscle groups (P > 0.05).
Conclusion: This study found significant sex differences in head kinematics during side-on impacts, with females experiencing greater head acceleration, especially in unpredictable conditions. Females also demonstrated slower RFD, which was associated with higher head acceleration. This association was stronger in the extension direction. Enhancing RFD, particularly in the early (0-150ms) phase, could help reduce head acceleration and should be a focus for injury prevention in females. These findings highlight the need for sex-specific, individualised training strategies to improve neck strength and RFD to better protect athletes from head and neck injuries in football.