Rehabilitation options for bone health after SCI focus on the application of electrical stimulation of the lower limb muscles and encouraging weight-bearing. This section includes six modalities: NMES, FES, standing and walking, treadmill training, ultrasound and physical activity/exercise. NMES is characterized by the application of high intensity, intermittent stimulation to produce strong visible isometric muscle contractions to elicit regional gains in strength with repeated stimulus exposure. (Maffiuletti et al. 2017). In contrast, FES consists of delivering moderate surface stimulation over specific muscles to replicate voluntary movements such as cycling, walking or rowing with the main goal of restoring function (Maffiuletti et al. 2017). These lifelong types of NMES and FES protocols are dedicated to maintaining neuromusculoskeletal health and are intended to be a substitute for a functional activity for patients that can no longer perform these movements by themselves in the absence of the device. On the other hand, FES-therapeutic (FES-T) is a form of FES where voluntary movement of a limb is initiated prior to application of the electrical stimulation in a specific pattern to augment voluntary movement, with the aim of withdrawing the device after 3-6 months of therapy and persistence of the movement is anticipated thereafter.
Weight-bearing activities, such as walking and standing, are also used for bone health after SCI; these modalities include either passive (tilt-table or standing frame) or active weight-bearing activities with or without assistance from FES. Many FES studies and weight-bearing studies have enrolled participants with both acute and chronic injuries and are therefore difficult to classify as pure prevention or treatment interventions. For this review, studies that enrolled participants that ranged from the acute phase to > 1 year were included with the treatment literature, as the majority of their participants were in the chronic phase.