People with spinal cord injuries (SCI) are at greater health risk for major health conditions and poorer health outcomes than the population without disabilities. For people with SCI, physical activity is critical for both physiological and psychosocial well-being, however 75% of persons with SCI are not active enough to achieve activity-related health benefits. While current exercise guidelines for persons with SCI are limited and vary, health authorities and literature have focused more on recommendations for moderate-intensity exercise, however recent studies have shown that, due to the reduced exercise capacity of the active muscles used in persons with SCI, moderate-intensity exercise alone is inadequate to stimulate meaningful improvements in cardiovascular disease risk. An alternative exercise approach that has demonstrated significant reductions in cardiovascular disease risk and morality is high-intensity interval training (HIIT). Participating in exercise protocols of higher intensity may offer a more effective and time-efficient method of increasing cardiovascular fitness and metabolic health in persons with SCI. However, few studies have evaluated the efficacy of HIIT protocols to increase exercise intensity and clinically improve cardio metabolic health and fitness in this population. The WheelMill System (WMS) is a wheelchair roller-based system that allows persons with SCI to use their personal manual wheelchair for wheelchair training or endurance exercise. With this study, we aim to assess the efficacy of a HIIT intervention conducted on a wheelchair roller-based system in improving cardiorespiratory and metabolic function, psychosocial well-being, and exercise intensity for manual wheelchair users (MWUs) with SCI. We also aim to determine if the roller-based system is a feasible platform for delivering HIIT for MWUs with SCI as well as identifying the perspectives of the participants on the recruitment and enrollment process, the assessment methods, and tolerance and acceptance of the intervention protocol. The long-term goal of this research is to increase cardiorespiratory fitness and reduce cardiovascular and metabolic disease risk in MWUs. This study will serve as the initial step toward that goal by pilot testing a HIIT intervention to increase exercise intensity of MWUs with SCI to promote physiological and psychosocial activity-related health benefits. We will recruit, enroll, and randomize MWUs with SCI into a roller-based Intervention Group (IG) or the Control Group (CG). Participants in the IG will complete an initial exercise education session and a 12-week (3 sessions/wk) evidence-based HIIT program using the roller-based system. Participants in the CG will complete an initial exercise education session and enroll in a 12-week (3 sessions/wk) independent workout program at an accessible community-based fitness facility. This study will measure the potential physiological, functional, and psychosocial health benefits of participating in a HIIT program designed for MWUs with SCI. We will then use the findings to define how exercise training at a higher intensity can support health outcomes and improve therapeutic and community-based interventions to promote cardiorespiratory and metabolic health and well-being of people with SCI.