The safety of aerobic exercise in the management of pediatric patients with post-concussion syndrome (PCS) has been established, but there is no existing data on exercise treatment for pediatric patients in the acute phase of recovery after sports-related concussion. While intensive exercise too soon after concussion has been associated with delayed recovery and used to justify prolonged periods of rest, recent studies have shown that controlled, sub-symptom threshold aerobic exercise may aid recovery by improving autonomic balance and cerebral blood flow auto-regulation after concussion. This study will randomly assign pediatric patients with concussion to a treatment group in which they will complete sub-symptom threshold aerobic exercise or to a placebo group in which they will complete a standardized stretching protocol. All participants will have routine clinical visits that consist of a physical examination and exercise test, which will be terminated with the exacerbation of symptoms.