This project consists of two parts: Robotic Rehabilitation Trials, and Study of Outcome Predictors and Clinimetric Attributes. In the first part of study, the investigators aim to (1) investigate the treatment effects of robot-assisted therapy (RAT) in patients with stroke on various outcomes, (2) test the dose-response relations by using two different intensities (higher versus lower intensity RAT), and (3) investigate the effects of the training intensity on a biomarker of oxidative stress. Treatment outcomes will encompass the spectrum of functioning including motor ability, motor control strategies, basic/extended daily functions, mobility, community reintegration, quality of life, and biomarker (8-OHdG). In the second part of study, the purposes are to define the appropriate populations for RAT and to examine the clinimetric properties of clinical measures relevant for use in robotic rehabilitation research. the investigators will identify the clinical predictors that will potentially influence the functional outcomes after interventions. Finally, the investigators will examine and compare the clinimetric properties (e.g., validity and responsiveness) of the clinical measures of rehabilitation outcome to inform selection of test instruments that may detect clinically meaningful change after rehabilitation therapy.

Inclusion Criteria:

1. 3 to 24 months onset from a first-ever unilateral stroke
2. an initial UL subsection of the Fugl-Meyer Assessment score of 18 to 56 indicating moderate to severe and moderate UL movement impairment
3. no excessive spasticity in any of the joints of the affected UL (shoulder, elbow, wrist, fingers)
4. be able to follow study instructions and perform study tasks
5. without upper limb fracture within 3 months
6. lack of participation in any experimental rehabilitation or drug studies during the study period
7. willing to provide written informed consent

Exclusion Criteria:

1. subjects exhibiting physician-determined major medical problems or poor physical conditions that would interfere with participation
2. subjects with excessive pain in any joint that might limit participation