Neurologic level of injury at or below cervical level 5 (C5) through C8 [tetraplegia] and at or below T1 through L3 [paraplegia]; persons with incomplete lesions at higher levels may be eligible, decided on a case by case basis depending on functional ability, Complete and incomplete injury allowed, Physical capability (ie, sufficient voluntary motor function) to participate in unassisted resistive exercise, determined as a minimum of grade 3 (by manual muscle testing) on elbow and wrist extension, Use of either a manual or power wheelchair as primary mobility, Absence of significant medical complications, Normal or nearly normal cognitive function (ie, minimal cognitive impairment may be allowed on a case by case basis), Willingness to participate for the duration of the study.