are stimulated to provide a standing posture. kralj's approach was extended by graupe et al. into a digital fes system that employs the power of digital signal processing to result in the parastep fes system, based on us patents 5,014,705 (1991), 5,016,636 (1991), 5,070,873 (1991), 5,081,989 (1992), 5,092,329 (1992) and related foreign patents. the parastep system became the first fes system for standing and walking to receive the us fda approval (fda, pma p900038, 1994) and become commercially available. the parastep's digital design allows a considerable reduction in rate of patient-fatigue by drastically reducing of stimulation pulse-width (100–140 microseconds) and pulse-rate (12–24 per sec.), to result, in walking times of 20–60 minutes and average walking distances of 450 meters per walk, for adequately trained thoracic-level complete paraplegics patients who complete training that includes daily treadmill sessions, with some patients exceeding one mile per walk. also, parestep-based walking was reported to result in several medical and psychological benefits, including restoration of near-normal blood flow to lower extremities and holding of bone density decline. walking performance with the parastep system greatly depends on rigorous upper body conditioning-training and on a completing 3–5 months of a daily one–two-hour training program which includes 30 of more minutes of treadmill training. an alternative approach to the above techniques is the fes system for walking developed using the compex motion neuroprosthesis, by popovic et al. . compex motion neuroprosthesis for walking is an eight to sixteen channel surface fes system used to restore voluntary walking in stroke and spinal cord injury individuals. this system does not apply peroneal nerve stimulation to enable locomotion. instead, it activates all relevant lower limb muscles in a sequence similar to the one that brain uses to enable locomotion. the hybrid assistive systems (has) and the rgo walking neuroprostheses are devices that also apply active and passive braces, respectively. the braces were introduced to provide additional stability during standing and walking. a major limitation of neuroprostheses for walking that are based on surface stimulation is that the hip flexors cannot be stimulated directly. therefore, hip flexion during walking must come from voluntary effort, which is often absent in paraplegia, or from the flexor withdrawal reflex. implanted systems have the advantage of being able to stimulate the hip flexors, and therefore, to provide better muscle selectivity and potentially better gait patterns. hybrid systems with exoskeleton have been also proposed to solve this problem. these technologies have been found to be successful and promising, but at the present time these fes systems are mostly used for exercise purposes and seldom as an alternative to wheelchair mobility. stroke and upper limb recovery in the acute stage of stroke recovery, the use of cyclic electrical stimulation has been seen to increase the isometric strength of wrist extensors. in order to increase strength of wrist extensors, there must be a degree of motor function at the wrist spared following the stroke and have significant hemiplegia. patients who will elicit benefits of cyclic electrical stimulation of the wrist extensors must be highly motivated to follow through with treatment. after 8 weeks of electrical stimulation, an increase in grip strength can be apparent. many scales, which assess the level of disability of the upper extremities following a stroke, use grip strength as a common item. therefore, increasing strength of wrist extensors will decrease the level of upper extremity disability. patients with hemiplegia following a stroke commonly experience shoulder pain and subluxation; both of which will interfere with the rehabilitation process. functional electrical stimulation has been found to be effective for the management of pain and reduction of shoulder subluxation, as well as accelerating the degree and rate of motor recovery. furthermore, the benefits of fes are maintained over time; research has demonstrated that the benefits are maintained for at least 24 months. drop foot drop foot is a common symptom in hemiplegia, characterized by a lack of dorsiflexion during the swing phase of gait, resulting in short, shuffling strides. it has been shown that fes can be used to effectively compensate for the drop foot during the swing phase of the gait. at the moment just before the heel off phase of gait occurs, the stimulator delivers a stimulus to the common peroneal nerve, which results in contraction of the muscles responsible for dorsiflexion. there are currently a number of drop foot stimulators that use surface and implanted fes technologies. drop foot stimulators have been used successfully with various patient populations, such as stroke, spinal cord injury and multiple sclerosis. the term "orthotic effect" can be used to describe the immediate improvement in function observed when the individual switches on their fes device compared to unassisted walking. this improvement disappears as soon as the person switches off their fes device. in contrast, a "training" or "therapeutic effect" is used to describe a long term improvement or restoration of function following a period of using the device which is still present even when the device is switched off. a further complication to measuring an orthotic effect and any long term training or therapeutic effects is the presence of a so-called "temporary carry over effect". liberson et al., 1961 was the first to observe that some stroke patients appeared to benefit from a temporary improvement in function and were able to dorsiflex their foot for up to an hour after the electrical stimulation had been turned off. it has been hypothesised that this temporary improvement in function may be linked to a long term training or therapeutic effect. this image describes functional electrical stimulation therapy for walking. the therapy was used to help retrain incomplete spinal cord injured individuals to walk . stroke hemiparetic stroke patients, who are impacted by the denervation, muscular atrophy, and spasticity, typically experience an abnormal gait pattern due to muscular weakness and the incapacity to voluntary contract certain ankle and hip muscles at the appropriate walking phase. liberson et al., (1961) were the first to pioneer fes in stroke patients. more recently, there have been a number of studies that have been conducted in this area. a systematic review conducted in 2012 on the use of fes in chronic stroke included seven randomized controlled trials with a total of 231 participants. the review found a small treatment effect for using fes for the 6-minute walking test. multiple sclerosis fes has also been found to be useful for treating foot drop in people with multiple sclerosis. the first use was reported in 1977 by carnstam et al., who found that it was possible to generate strength increases through using peroneal stimulation. a more recent study examined the use of fes compared to an exercise group and found that although there was an orthotic effect for the fes group, no training effect in walking speed was found. further qualitative analysis including all participants from the same study found improvements in activities of daily living and a reduced number of falls for those using fes compared with exercise. a further small scale (n=32) longitudinal observational study has found evidence for a significant training effect through using fes. with nmes treatment there were measurable gains in ambulatory function. however, a further large observational study (n=187) was supportive of previous findings and found a significant improvement in orthotic effect for walking speed. cerebral palsy fes has been found to be useful for treating the symptoms of cerebral palsy. a recent randomised controlled trial (n=32) found significant orthotic and training effects for children with unilateral spastic cerebral palsy. improvements were found in gastrocnemius spasticity, community mobility and balance skills. a recent comprehensive literature review of the area of using electrical stimulation and fes to treat children with disabilities mostly included studies on children with cerebral palsy. the reviewers summarised the evidence as the treatment having the potential to improve a number of different areas including muscle mass and strength, spasticity, passive range of motion, upper extremity function, walking speed, positioning of the foot and ankle kinematics. the review further concludes that adverse events were rare and the technology is safe and well tolerated by this population. the applications of fes for children with cerebral palsy are similar to those for adults. some common applications of fes devices include stimulation of muscles whilst mobilizing to strengthen muscle activity, to reduce muscle spasticity, to facilitate initiation of muscle activity, or to provide a memory of movement. national institute for health and care excellence guidelines (nice) (uk) nice have issued full guidelines on the treatment of drop foot of central neurological origin (ipg278). nice have stated that "current evidence on the safety and efficacy (in terms of improving gait) of functional electrical stimulation (fes) for drop foot of central neurological origin appears adequate to support the use of this procedure provided that normal arrangements are in place for clinical governance, consent and audit". in popular culture mark coggins' novel no hard feelings (2015) features a female protagonist with a spinal cord injury who regains mobility via advanced fes technology developed by a fictional biomedical startup.