Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Health and Rehabilitation Sciences


Dickey, James P.

2nd Supervisor

Walton, David M.

Joint Supervisor


Head trauma that occurs during sporting events is responsible for an increasing number of emergency department visits in Canada and is associated with an increased risk of developing neurodegenerative diseases.While head injury in American football has been extensively studied, it cannot be extrapolated to non-helmeted sports. Approximately 265 million people are actively participating in soccer and many are 18 years of age and younger. Soccer is unique in that players use their head to redirect the ball; however, the effects of cumulative purposeful soccer heading on brain health are unknown. Accordingly, the objective of this thesis was to quantify head impact magnitudes that female youth soccer players sustain during games and evaluate their influence on electrophysiological functioning both at rest and exercise. This was achieved through three research projects that studied female youth soccer players for an entire soccer season and investigated repetitive soccer heading using methodological equipment including, game video analysis, headbands instrumented with wireless microsensors, as well as electroencephalogram (EEG) recordings. Results indicated that the median number of headers experienced during a single game was one, while the maximum is nine, and minimum is zero (Chapter 2). Furthermore, player age is positively associated with an increasing number of purposeful soccer headers, but there is no association between head impact location and game scenario (Chapter 2). Chapter 3 reveals that game scenario and head impact location significantly affect both linear head acceleration and rotational head velocity magnitudes. As an initial attempt to detect neurocognitive change (Chapter 4), EEG recordings revealed a statistically significant increase in EEG power during exercise compared to rest at each EEG frequency band (Alpha1, Alpha2, Beta1, Beta2, Theta). These differences were amplified when cumulative number of headers were considered, but only for Alpha1, Alpha2 and Beta2. In conclusion, this thesis shows cumulative soccer heading experienced by female youth soccer players could lead to neurocognitive changes after one season of soccer. Furthermore, exercise may help to reveal sub-clinical brain changes due to cumulative soccer heading that are not shown at rest. These findings can help guide data-driven approaches to improve player safety in youth soccer.

Summary for Lay Audience

While there are numerous personal and societal benefits from participation in sport, head injuries are a healthcare concern that are responsible for an increasing number of emergency department visits. More recently, evidence highlights that repetitive head impacts experienced through sport may be responsible for the onset of long-term cognitive deficits including Alzheimer’s Disease and Chronic Traumatic Encephalopathy (CTE). Considerable research has evaluated American football, while females and adolescents are understudied; even though females have a higher rate of head injury compared to males, and adolescents report more prolonged symptomology. In soccer, players experience repetitive head impacts through purposeful soccer heading; however, their cumulative effects are unknown. Determining the relationship between purposeful soccer heading and brain function can help inform evidence-based interventions to improve player safety. Accordingly, this thesis seeks to delineate the relationship between repetitive head impacts and brain health by evaluating purposeful soccer heading in female youth soccer players. Game video was recorded during an entire season of soccer, and players wore headbands containing microsensors to quantify head impact accelerations. Purposeful headers were characterized by head impact location (front, top, side), player position (defense, midfield, forward) and game scenario (corner kick, throw in, goal kick etc.). In addition, measures of brain activity were collected using electroencephalogram (EEG) recordings to determine changes in brain function, related to cumulative purposeful soccer heading. The findings from this thesis indicate that female youth soccer players frequently head the ball during soccer games, and increasing player age is associated with an increasing number of headers experienced. In addition, the head impact accelerations that result from purposeful soccer heading depend on game scenario as well as head impact location. Lastly, our EEG measures indicate that brain activity increases compared to rest during combined exercise and cognitive load, and that an increasing number of cumulative headers amplifies this difference. These results provide important information to help develop evidence-based criteria to reduce the risk of head injury that results from repeated head impacts, and could improve the safety of players in the short- and long-term.