Transcutaneous spinal cord stimulation (tSCS) is a noninvasive neural stimulation technique that can be used to activate the dorsal roots of the spinal cord. By delivering current via electrodes placed on the surface of the skin, spinal cord excitability can be inferred by measuring spinal reflexes. One such reflex is called the Posterior Root Muscle (PRM) reflex, which is evoked by activating the dorsal roots of the spinal cord. In this research project, the PRM reflex was used to investigate differences in spinal cord excitability across people of different ages. These data were used as a control to determine how spinal cord excitability changes after lower-limb amputation. A stimulation electrode was placed on the back over the T12-L1 spinal vertebrae and a return electrode on the ipsilateral anterior superior iliac spine. Muscle responses were recorded from the tibialis anterior, medial gastrocnemius, lateral gastrocnemius, and soleus muscles using electromyography. Electrical pulses were delivered at amplitudes ranging from each participant's PRM reflex threshold (lowest amplitude at which a PRM reflex was evoked) and maximum (amplitude at which the magnitude of the PRM response no longer increased). Preliminary data indicates that PRM reflex thresholds may increase naturally with age, suggesting a decrease in spinal cord excitability over the lifespan (R² = 0.017). It is expected that age-matched comparisons of PRM thresholds between controls and individuals with a lower-limb amputation will indicate a further decrease in spinal cord excitability post-amputation. Conclusions from this study will aid in assessing the effects of chronic use of tSCS in populations with lower-limb amputation and how it may reduce phantom limb pain.