Inclusion Criteria:  To be included, participants will have to:  Be 18-65 years of age Have history of traumatic SCI ( 1-year) with NLI of C8-T10 and AIS A or B (confirmed by AIS examination performed by PI or a qualified Provider Have a caregiver who is available and willing to be trained to apply intervention protocol in the home (placing weights and positioning the Veteran) throughout study duration Be a wheelchair user for primary mode of mobility Have Knee extensors that must respond to standard surface electrical stimulation procedures (stimulation frequency procedures, 30 Hz; pulse duration:1 ms and amplitude of the current of less than200 mA) Be able to receive written clearance from their medical Providers to ensure safety of participants Be a Veteran (male or female), however, the Department of Veteran Affairs has limited number of female Veterans, especially those with motor complete injury at level C8-T10 (currently, there are only 3 female Veterans with the target NLI in our SCI registry). Hence, inclusion of women Veterans may be challenging due to this disparity in the SCI population. If we fail to recruit 20 Veterans, we may seek an IRB approval to recruit non-Veterans to meet our target sample size Have normal ECG Commit to undergo 9 months of trial; 4.5 months of open-kinematic chain resistance training followed by 4.5 months of closed-kinematic chain using simple rowing approach + Vit. D supplementation (Experimental group) or 9 months of passive movement +Vit D supplementation (control group)  Exclusion Criteria:  Potential participants will be excluded if they exhibit any of the following:  Neurological injury other than SCI Older than 65 years of age as they may likely have considerable amount of bone loss at that age Have severe osteoporosis because loading porous/fragile bone by electrical stimulation may result in bone fracture Those classified as AIS C & D, as they may already be engaging in weight bearing activities that may confound the results of this trial Unhealed or unstable fractures in either lower or upper extremities Severe scoliosis, deformities in the hip, knee, or ankles OR impaired range-of-motion, as these could be a barrier to safe positioning on the rowing machine, and on MRI or DXA tables No caregiver or family member/significant other, willing to help with placing weights and positioning participants' lower extremities on the rowing machine Untreated or uncontrolled hypertension (systolic blood pressure (BP) > 140 mmHg; diastolic BP > 90 mmHg), and/or sudden hypotension upon transferring from bed to wheelchair, characterized by a drop in BP by 20 mmHg (especially in persons with tetraplegia) or heart rate > 100 beats per minute Anti-coagulation or anti-platelet therapy (including aspirin) Implanted pacemakers, implanted defibrillator devices or any metallic implants including knee or hip implants Presence of bullets in vertebral column or shrapnel anywhere in the body that may interfere with MRI procedure Other medical conditions including cardiovascular disease, uncontrolled type II DM, active deep vein thrombosis (DVT), uncontrolled autonomic dysreflexia, use of insulin for DM management, pressures injuries of stage 3 or higher, or active urinary tract infection Severe hypercalcemia (serum calcium > 16mg/dl), stage III-V kidney disease, post-menopausal or estrogen dependent female, and men undergoing anti-androgen therapy or are post orchiectomy DXA total body T-score less than -2.5. Total hip BMD T-scores < -3.5 and knee BMD scores of less than 0.6 g/cm2 Untreatable severe spasticity bearing on potential participants' activities of daily living, such as transfers from bed to wheelchair or maintaining position in wheelchair Any psychiatric illness confounding judgment or cognitive impairment in participant or caregiver who is expected to help participant in the trial Those with prosthetic lower limbs Any condition that, in the judgment of the PI or other medical Providers, preclude safe participation in the study and/or has the potential to expose/increase participant's risk of infection Unable to tolerate increasing either electrical stimulation current or weights to the lower legs for any reason