This is a minimal risk randomized controlled trial whose aim is to test the efficacy of an exercise intervention (STEP) for youth 11-18 yo with persistent concussive symptoms (1-6 months inclusive). The investigators are utilizing an active control (light stretching). The primary outcome will be concussion symptoms measured with the Health-Behavior Inventory (HBI) in the first month after randomization. Long-term efficacy will be examined using standardized measures of quality of life and function over 6 months, and potential mediators will be explored including brain derived neurotrophic factor (BDNF), fear-avoidance and physical fitness. Physical activity will be measured with accelerometry to evaluate fidelity.
