The purpose of this study is to demonstrate that a robot-aided rehabilitation protocol that follows the "assist-as needed" paradigm provide statistically significant improvements in arm and hand motor functions when compared to robot-aided protocols that passively move patients' arms along pre-defined trajectories, in patients with incomplete spinal cord injury (SCI).

Twenty adults with chronic incomplete SCI (according to American Spinal Injury Association (ASIA) Impairment Scale (AIS) C-D level) will be recruited from TIRR and from the Houston area.

Inclusion Criteria:

1. Providing written informed consent prior to any study related procedures;
2. Age between 18-75 years;
3. Diagnosis of chronic complete or incomplete spinal cord injury as defined by the American Spinal Injury Association Impairment scale classification and at least for 6 months;
4. Not being involved in any specific exercise program (e.g., NMES, FES) within the previous 3 months;
5. No planned alteration in upper-extremity therapy or medication for muscle tone during the course of the study;
6. Eligibility for standard rehabilitation at the time of enrollment (i.e., absence medical comorbidities that would prevent standard rehabilitation);
7. No condition (e.g., severe arthritis, extreme shoulder pain) that would interfere with valid administration of the measures or with interpreting motor testing;

Exclusion Criteria: Subjects will be excluded if they have:

1. Any joint contracture or severe spasticity in the affected upper extremity, as measured by a Modified Ashworth Score > than 3 out of 4;
2. Subject who cannot provide self-transportation to the study location.