Inclusion Criteria:  a clinically stable spinal cord injury (above T11) that occurred at least one year previously the ability to ambulate at least 10 m with or without an assistive device (i.e., walker, crutches, or cane, not parallel bars) within 100 sec (those with 10-meter walking time >100 sec are excluded because it is unlikely that they are able to participate in and complete our planned locomotion evaluation procedures) clinical signs of spasticity in the plantarflexor muscles at least unilaterally (i.e., hyperreactivity to Achilles tendon tap, and increased muscle tone, score >1 on Modified Ashworth scale) spastic hyperreflexia reflected in exaggerated H-reflex functionally and medically stable for at least 3 months medical clearance to participate reasonable expectation that current medications (including antispasticity medication such as baclofen, diazepam, and tizanidine) will not change over the conditioning period. Each participant's medication and dosage will be monitored and recorded throughout the study. Once enrolled, the subject will remain enrolled even if medication changes. (Because only neurologically stable subjects will enter this study, medication changes will be unlikely.)  Exclusion Criteria:  motoneuron injury; a cardiac condition (history of myocardial infarct, pacemaker use, etc.) an unstable medical condition a pre-existing or confounding neurological condition (e.g., history of Multiple Sclerosis (MS), Traumatic Brain Injury (TBI), Stroke, Parkinson's disease) a condition that prevents lower extremity mobility testing or weight bearing (e.g. fracture, severe sprain/strain, botox muscular injection) (orthotic knee hyperextension is not excluded; in severe cases of knee hyperextension, the brace can be worn during the study sessions) a cognitive impairment that precludes giving informed consent (e.g., severe intellectual disability) use of a functional electrical stimulation (FES) foot-drop stimulator or an FES bicycle on a daily basis (FES applied to the arm is acceptable) deep vein thrombosis within the past 6 months depression (due to potential interference of anti-depressant medication with the intervention and possible reduced participation reliability) pregnancy (due to expected changes in weight and posture and potentially unstable medical condition).