Concussions are diffuse injuries that affect areas of the brain responsible for a person's physical, cognitive, and emotional health. Although concussions were once thought only to present transient symptoms, mounting evidence suggests potential for long-term neurological impairments. The deleterious effects of concussion can be from a single, high severity impact event or the accumulation of lower severity impacts. Clinical changes that can result from concussion include an elevated symptom presentation and changes in gait, or an individual's walking pattern. It is not well understood if similar deficits result after an accumulation of subconcussive impacts. The majority of research on human tolerance to head injury has been based on American football, using helmet-mounted sensors in male athletes. Limited studies have attempted to quantify biomechanical tolerance in women, despite the sex-specific nature of presentation and outcome of concussion. Biomechanical, physiologic, and psychosocial factors differ between males and females, likely contributing to this difference.

The research presented in this dissertation was aimed at describing sex-specific outcomes of subconcussion in a matched cohort of male and female athletes to gain a better sense of unhelmeted, sex-specific tolerance to head impacts. On-field data were collected from collegiate rugby players using instrumented mouthguards. Rugby involves high energy, frequent head impacts, does not require protective headgear, and is played the same for both men and women. The females in our study sustained fewer impacts per session than the males, but their impacts had similar linear acceleration magnitudes. The kinematics of the concussive male impacts were higher than the kinematics of the concussive female impacts. Both sexes reported concussion-like symptoms in the absence of diagnosed concussion during a season. Females reported more symptoms with a higher severity in-season compared to males after subconcussive and concussive impacts. Female athletes saw deficits in cadence, double support time, gait speed, and stride length post-concussion. The majority of athletes improved in their dual-task gait assessment by the end of the season, suggesting there may not be a negative effect on gait after an accumulation of subconcussive impacts. This work assessed the biomechanics of head impacts and concussions of this population, and evaluated changes in symptom presentation through weekly graded symptom surveys and dual-task gait assessments both after a concussion and as an effect of subconcussive impacts. Understanding the sex-specific clinical effects of head impacts is critical, and can provide insight into concussion diagnostic, management, and prevention tools that are appropriate and effective.