Study design: Review article. Objectives: To provide an overview of free radical biology, particularly with respect to muscle physiology, as well as the potential effects of muscle morphological changes, physical capacity and nutritional status on oxidative stress in people with chronic spinal cord injury (SCI). The potential implications of these factors for determining the optimal dosage of rehabilitation training interventions in people with chronic SCI will also be presented. Setting: Vancouver, BC, Canada. Methods: Literature review. Results: Not applicable. Conclusion: There has been a great deal of focus on rehabilitation exercise interventions providing intensive practice of movements to enhance functional recovery and physical capacity following SCI. However, there is still much to be understood about the appropriate dosage of training parameters (e.g. frequency, duration). It has been known for several decades that exercise increases free radical production, leading to oxidative stress. To date, there has been little consideration of the potential interaction of oxidative stress with training parameters on functional outcomes in chronic SCI. Furthermore, individuals with chronic SCI face many secondary consequences of their injury, such as muscle atrophy, change in muscle fiber type, general deconditioning and nutritional status, that are known to influence free radical production and antioxidant capacity. Better understanding of the potential confounding effects of oxidative stress associated with exercise will improve our ability to determine the optimal 'dose' of rehabilitation training to maximize functional recovery following SCI.