• Change in Upper Extremity Fugl-Meyer Assessment Motor (FMA) Score [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), 1 time per week during intervention, immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The Fugl-Meyer Assessment of Motor Recovery after stroke evaluates and measures recovery in post-stroke hemiplegic patients. It is used in both the clinical and research settings, and is one of the most widely used quantitative measures of motor impairment. Areas of assessment include activities of daily living, functional mobility, and pain. Different movements are judged on the individuals ability to perform with full capacity, limited capacity, or total inability to complete the movement. Scores range from 0-66, with 0 and 66 representing no and normal residual upper extremity motor function, respectively.
• Change in Quantitative measure of hand opening area and closing force [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), 1 time per week during intervention, immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  Individual will be instructed to rest paretic hand on a cylinder that is covered with an array of pressure sensors (Pressure Profile Systems, Inc., Los Angeles, CA 90045). Furthermore, 5 markers (9x9 mm) with unique optical features will be placed on the tip of the thumb and the 4 fingers. Individual will then be instructed to perform following task in their comfortable pace: 1) resting, 2) maximally open the paretic hand, and 3) maximally close the paretic hand against the cylinder. Position (with an accuracy of 1mm) and angular (with an accuracy at 0.02 degree) information of fingertips will be captured by 2 registered portable Moire Phase Tracking cameras (Metria Innovation, Inc., Wauwatosa, WI); and the flexion force under the 4 fingers and thumb will be measured by the pressure sensors. This will allow for tracking of the hand pentagon area and closing force during intervention.
• Change in Sensory Assessment (Stereognosis) [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), 1 time per week during intervention, immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The individual will be asked to use their paretic hand to identify a number of everyday items through touch alone. Scores range from 0-24, with 24 indicating full stereognosis function and 0 representing complete absence of stereognosis.
• Change in Cutaneous Sensory Touch Threshold using Semmes-Weinstein Monofilaments [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), 1 time per week during intervention, immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The monofilament test is a threshold assay used to determine the minimum stimulation that can be felt by a subject. This test is also known as light touch/protective touch/deep pressure testing in the hands. The threshold of detection for human tactile cutaneous receptors has been measured with as low as a few milligrams of force.
• Change in Stroke Impact Scale (SIS) [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The SIS is a 59 item measure of strength, hand function, activities of daily living, mobility, communication, emotion, memory, and participation. Each item is rated in a 5 point scale in terms of difficulty experienced in completing the item, ranging from 1 (could not do it at all) to 5 (not difficult at all).
• Change in Action Research Arm Test (ARAT) [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), 1 time per week during intervention, immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The ARAT test is a 19-item measure divided into 4 sub-tests (grasp, grip, pinch, and gross arm movement). ARAT is a validated quick (within ten to fifteen minutes) assessment of the paretic arm's functional disabilities, which offers uncomplicated and comprehensive feedback on the function of their arm, hand and fingers. Scores on the ARAT may range from 0-57 points, with a maximum score of 57 points indicating better performance.
• Change in Chedoke McMaster Stroke Assessment (CMSA) Hand Subscale [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  This test evaluate the stage of motor recovery for the paretic hand. Scores range from 0-7, with 7 representing full function of the hand.
• Change in Revised Nottingham Sensory Assessment: Kinaesthesia Subscale [ Time Frame: This will be measured pre-intervention (within 1 week prior to intervention), immediately after conclusion of intervention (within 1 week), and at a 3 month follow up ]
  The kinaesthesia subscale measures an individuals ability to sense movement, direction of movement, and position sense at a given joint. The assessment involves the tester initiating passive movement in the individuals affected finger, wrist, elbow, and shoulder; while the individual attempts to match those movement with their opposite extremity. Scores for each joint range from 0-3, with 3 representing intact position, direction, and sense of movement.

Individuals with moderate to severe stroke will be recruited for both lab-based testing and home-based practice:

1. Pre-training clinical evaluation (lab-based). In this session, a research physical therapist will evaluate the participant's arm function and impairment level using standardized clinical assessments to ensure eligibility for participating in this study. Once confirmed, a set of standardized clinical assessments will be conducted by the research physical therapist as the baseline assessments of the participant's hand/arm function. This visit is expected to last approximately 3 hours.
2. Pre-training device setup (lab-based). The participant will be randomly assigned to one of the recruited physical therapists (PTs) or senior student physical therapists (SPTs) who has been recruited and consented to participate in this study. The assigned PT will determine 1) the electrode positions for recording the participant's muscle activities during the performance of different arm/hand functions, and 2) the stimulation electrode positions and stimulation intensities for achieving the best hand opening with the forearm at the individual's mid-range of available supination/pronation. Then, the corresponding electrode positions will be marked, and the forearm/hand with these markers will be scanned. This visit is expected to last approximately 3 hours. The scanned results will be used offline to develop a forearm-hand orthosis (FHO) that fits the participant's forearm and hand. During this visit, the investigators will measure the time for the PT/SPT to set up 1) recording electrodes, 2) detecting rules, 3) stimulation electrodes and configuration, and 4) the time for scanning.
3. Pre-training device-use learning sessions (2 visits, lab-based). After the FHO is ready, the participant will be called to participate in the 1st and 2nd lab-based training sessions for the use of ReIn-hand device. During these 2 visits, the assigned PT/SPT (1st test) or the research PT (2nd test) will train the participant to use the FHO and the ReIn-Hand software on a mobile device, until the participant demonstrates the ability in using the device independently twice in a row. During these 2 visits, the investigators will measure the time for the participant to 1) learn the use of the ReIn-Hand device (from the start of the session to the time that the participant is able to demonstrate ability to independently use the device twice in a row), 2) attach the FHO, 3) use the software for 1 trial (including connecting all the cables following the instructions, start the software and finish 1 trial), and 4) clean up. At the end of the 1st (for PTs) or the 2nd (for individuals with stroke) learning sessions, a 5min user survey will be conducted to report the level of ease-of-use of the ReIn-Hand device. During the 2nd learning session, the participant will also be re-tested on part of the clinical assessments, however, this time with the assistance of the ReIn-Hand device. Each of these 2 visits is expected to last about 3 hours.
4. Pre-training 2nd baseline clinical measures (lab-based). Within one week prior to starting the Home-based practice, a research PT will conduct the 2nd baseline clinical measures, which will repeat the 1st baseline clinical measures with an additional quantitative measure of maximal hand opening area and closing force (QMHOC). For QMHOC, pressure sensors (Pressure Profile Systems, Inc., Los Angeles, CA 90045) in conjunction with portable Moire Phase Tracking cameras (Metria Innovation, Inc., Wauwatosa, WI) will be used. The whole QMHOC will take about 10 minutes, and the whole 2nd baseline clinical measure session will take about 2 hours.

5. Pre-training EEG measures (lab-based). Within one week prior to starting the Home-based practice and within one week following completion of the 12-week Home-based practice, the participant will take part in an EEG experiment. During this session, a 9x9 mm marker will be placed on the tip of each finger, with another on the back of the hand as reference, which will allow for the measure of the position and angle of the fingers/hand by 2 portable Moire Phase Tracking cameras (180 Hz; Metria Innovation Inc. Milwaukee, WI). In addition, surface EEG electrodes will be mounted on a stretchable fabric cap based on the 10/20 system. A Polaris Krios handheld scanner and reflective markers (NDI, Ontario, Canada) will be used to record the EEG electrode positions compared to the coordinate system defined by the nasion, inion, and pre-auricular notches. Eye movement detection electrodes will also be placed on the supra- and infra-orbital margins for detection of vertical eye movement. EMG will be recorded from the extensor carpi radialis, flexor carpi radialis, and deltoid of the arm.

   Once prepared, the participant will be seated in an experimental chair with: 1) adjustable straps across the shoulders and waist to maintain proper posture, 2) paretic forearm attached to an orthosis that is linked to the ACT-3D, a robot that will provide required arm support, 3) hand around a cylinder with a custom pressure sensor mat (Pressure Profile System Inc., CA). The participant will be instructed to perform 1 of 2 movements: 1) hand opening while resting on a haptic table, or 2) hand opening while lifting against 50% of their maximum shoulder abduction force. The investigator will measure scalp recordings and EMG recordings using a 160-channel EEG/EMG system using active electrodes (Biosemi, Inc., Active II, Amsterdam, The Netherlands), hand opening area or finger flexion force.

6. Home-based practice. After above 5 lab-based visits, participants will take the ReIn-Hand device, including the FHO, the mobile device with ReIn-Hand software, and the electronic stimulator (300 PV, Empi, Minnesota, USA, a FDA approved clinical device) back home. At home, participants will perform 20 trials of pre-set tasks, like reaching and grasping, per session (1 hour), 1 session per day, 7 days per week for 12 weeks. During these 12 weeks, the participant will visit the lab once per week to make necessary device changes, and perform part of the clinical assessments and QMHOC measure without the ReIn-hand.
7. Post-training tests (lab-based). The sessions #4 mentioned above will be repeated at one week and 3-month after the 12-week home-based practice. The session #5 will be repeated at one week after the 12-week home-based practice. All the post-training tests will be preformed without ReIn-hand device.

• Stroke
• Hand Function

Inclusion Criteria:

• Age between 21-80
• Paresis confined to one side, with substantial motor impairment of the upper limb and some residual voluntary movement (UE FMA in the range of 10-40/66, CMSA_H stage of the hand section <=4)
• Normal Cognitive ability (MOCA score >=24)
• Capacity to provide informed consent
• Ability to elevate their limb against gravity up to at least 75 degrees of shoulder flexion and then to generate some active elbow extension
• Ability to open hand with a thumb-to-index finger distance ≥4 cm, with the assistance of the ReIn-Hand device with the help of a physical therapist
• Discharged from all forms of physical rehabilitation
• Intact skin on the hemiparetic arm

Exclusion Criteria:

• Motor or sensory impairment in the non-affected limb
• Any brainstem and/or cerebellar lesion
• Severe concurrent medical problems (e.g. cardiorespiratory impairment, uncontrolled hypertension, inflammatory joint disease)
• History of neurologic disorder other than stroke (Parkinson's Disease, Amyotrophic Lateral Sclerosis, Multiple Sclerosis, Traumatic Brain Injury, peripheral neuropathy)
• Any acute or chronic painful condition in the upper extremities or spine, indicated by a score ≥5 on a 10-point visual analog scale
• Using cardiac pacemaker
• Seizure
• Severe upper extremity sensory impairment indicated by absent sharp-blunt discrimination on the tactile sensation subscale of the Revised Nottingham Sensory Assessment( the score >=1 on anterior and posterior forearm)
• Chemo denervation: botulinum toxin injection to any portion of the paretic UE within the last 6 months, or phenol/alcohol injections <12 months before participation
• Unable to passively attain 90 degrees of shoulder flexion and abduction, measured using a goniometer based on adapted methods
• Flexion contractures larger than 30 degrees in the elbow, wrist, metacarpophalangeal joints (MCP) and interphalangeal joints (IP)
• Pregnant or planning to become pregnant
• Upper extremity musculoskeletal impairment limiting function prior to stroke.