Concussions are very common. Although many people recover well from concussion, some will have persistent symptoms and difficulties with daily activities. How people cope with their symptoms following concussion powerfully influences their recovery. Fear avoidance behaviour is a particularly unhelpful approach to coping, in which people perceive their pre-injury activities as unnecessarily dangerous and take great care to avoid overexertion and overstimulation. The investigators developed and pilot tested a behavioural therapy, called graded exposure therapy, to reduce fear avoidance behaviour. Our preliminary work suggested that graded exposure therapy was acceptable to patients with concussion and possibly beneficial for their recovery. The GET FAB after concussion study will assess the effectiveness of graded exposure therapy.

GET FAB is a multisite randomized controlled trial designed to evaluate a behavioural treatment (graded exposure therapy) for adults with persistent symptoms after concussion. Participants in this study will be recruited from a network of concussion clinics in Canada. This study follows from the investigators' prior work establishing that (1) fear avoidance behaviour is a risk factor for poor concussion outcome, (2) graded exposure therapy reduces fear avoidance behaviour, and (3) graded exposure therapy is perceived as credible and is well-tolerated by patients with persistent post-concussion symptoms.

Participants will be assigned at random (in a 1:2:2 ratio) to receive enhanced usual care, graded exposure therapy group, or another therapy that might have similar benefits (prescribed aerobic exercise). The investigators hypothesize that patients who participate in graded exposure therapy will have reduced fear avoidance behaviour and improved daily functioning compared to other treatment conditions and this difference will be greatest for patients who enter the study with high fear avoidance behaviour.

Inclusion Criteria:

1. aged 18-70 years;
2. sustained a concussion according to the ACRM mTBI Task Force definition between 1 and 24 months ago
3. fluent in English, because validated translations are not available for most questionnaires and recruiting multilingual therapists is not feasible;
4. access to a computer, tablet, or smartphone with internet capability;
5. 3 or more moderate-severe symptoms on the Rivermead Postconcussion Symptom Questionnaire.

Exclusion Criteria:

1. medical contraindication to aerobic exercise (cardiac disease, chest pain with exertion, acute bone/joint/soft tissue injury aggravated by exercise)
2. change in cardiac medication within the last month, such as beta blockers, calcium channel blockers, or ivabradine
3. involved in personal injury litigation for index mTBI
4. currently pregnant or plan to become pregnant within the next three months
5. severe/unstable medical or psychiatric condition that could worsen over the next year")

Deidentified participant data (including data dictionaries).

Immediately following publication. No end date.

Upon reasonable request. Requests can be made to the Principal Investigator.

Participants will be blinded to the study hypotheses and treatment arms, but not to the type of intervention they are receiving. Outcome assessors will be blinded to participants' treatment assignments.