Inclusion Criteria:  Concussed Cohort  18-40 years old. Concussed active duty Service members and physically active civilians cleared for full RTD/A. Recruited within 5 days following being medically cleared for full RTD/A post-concussion. Access to a functional email address and the internet for completion of patient reported outcomes (PROs) and musculoskeletal injury measures.  Non-Concussed Cohort  18-40 years old. Active duty Service members and physically active civilians. No self-report history of concussion within the previous 5 years. No lingering post-concussion signs/symptoms. Within ±5% of the matched concussed participant's height, weight, and body mass index. Within ±2 years of age of the matched concussed participant. Participant in the same physical activities (work, recreational sports, average type [no impact, low-impact, high-impact] and duration of physical activity)  Exclusion Criteria:  Post-Concussion Cohort AND Healthy Non-Concussed Cohort  Unable to read or comprehend the English language. Admitted to the hospital following concussion. Sustained a concussion not related to physical activity participation (e.g., blast-related injury, fall from a ladder, motor vehicle accident). Loss of consciousness longer than 30 minutes. Alteration in consciousness longer than 24 hours. Post-traumatic amnesia lasting longer than 1 day. Glasgow Coma Scale below 13. Abnormal brain imaging findings. Sustained a concussion that took longer than 21 days for the individual to RTD/A. A MSKI within the last 6 months that resulted in altered or missed physical activity for 3 or more consecutive days. History of MSKI surgery. Pregnant females (will be eligible for participation in the study once medically cleared to RTD/A by a qualified and licensed healthcare provider following the end of the pregnancy).