This paper describes the course of wheelchair propulsion capacity (WPC) during rehabilitation of persons with spinal cord injury (SCI) and its relationship with personal and injury characteristics. We investigated 132 subjects with SCI (37 with tetraplegia) at the start of active rehabilitation (t1), 3 months later (t2), and at the end of clinical rehabilitation (t3). WPC was measured as the maximal power output that can be achieved in a maximal wheelchair exercise test on a treadmill. Results were analyzed with the use of generalized estimating equations, with time of measurement, lesion level, motor completeness of the lesion, age, and gender as independent variables. Overall, WPC increased from 30.5 W at t1, to 39.5 W at t2, and 44.2 W at t3. Persons with paraplegia, persons with incomplete lesions, men, and younger persons had higher values for WPC compared with persons with tetraplegia, persons with complete lesions, women, and older persons. Rate of improvement was lower in older persons and women compared with younger persons and men. This paper identifies factors that affect the level (lesion level, completeness of the lesion, age, gender) and rate of improvement (age, gender) of WPC during rehabilitation. These findings should be considered when wheelchair capacity training is applied in SCI rehabilitation.