Inclusion Criteria:  ≥ 18 years old ≥ 12 months post-SCI and medically/neurologically stable Cervical spinal cord injury (C1-C8); any etiology except neurodegenerative conditions Unable to grasp objects independently with both hands (tetraplegia) Manual muscle testing (MMT) scores ≥4/5 for elbow flexion and ≥2/5 for wrist extension Willing to participate in sessions at home or able to travel to alternate site for study sessions  Exclusion Criteria:  Ventilator-dependent (dependent upon mechanical life support due to inability to breathe effectively) Poorly controlled autonomic dysreflexia (more than one episode in 3 months prior to enrollment) Moderate to severe spasticity (Modified Ashworth Scale (MAS) >1+) in the hand, wrist, or forearm Received a localized injection (e.g. Botox) to hand, wrist, or forearm muscles within past 12 months Currently participating in physical rehabilitation for upper extremity impairments Individuals having or requiring any of the following: implanted pacemaker, life supporting/sustaining equipment, or critical non-removable implantable electronic devices such as an insulin pump or neurostimulator. Presence of any other clinically significant medical comorbidity and/or neurological condition for which participation in the study may pose a safety risk and/or influence results Presence of the following medical conditions: uncontrolled seizure disorder, active malignancy in the upper extremities, or open wounds/infections in the upper extremities Individuals whose forearm is determined to be too small or too large to fit the electrode sleeve being investigated Individuals who are pregnant or plan to get pregnant during the course of the study