Technology-Based Feedback and Its Efficacy in Improving Gait Parameters in Patients with Abnormal Gait: A Systematic Review

This systematic review synthesized and analyzed clinical findings related to the effectiveness of innovative technological feedback for tackling functional gait recovery. An electronic search of PUBMED, PEDro, WOS, CINAHL, and DIALNET was conducted from January 2011 to December 2016. The main inclusion criteria were: patients with modified or abnormal gait; application of technology-based feedback to deal with functional recovery of gait; any comparison between different kinds of feedback applied by means of technology, or any comparison between technological and non-technological feedback; and randomized controlled trials. Twenty papers were included. The populations were neurological patients (75%), orthopedic and healthy subjects. All participants were adults, bar one. Four studies used exoskeletons, 6 load platforms and 5 pressure sensors. The breakdown of the type of feedback used was as follows: 60% visual, 40% acoustic and 15% haptic. 55% used terminal feedback versus 65% simultaneous feedback. Prescriptive feedback was used in 60% of cases, while 50% used descriptive feedback. 62.5% and 58.33% of the trials showed a significant effect in improving step length and speed, respectively. Efficacy in improving other gait parameters such as balance or range of movement is observed in more than 75% of the studies with significant outcomes. Conclusion: Treatments based on feedback using innovative technology in patients with abnormal gait are mostly effective in improving gait parameters and therefore useful for the functional recovery of patients. The most frequently highlighted types of feedback were immediate visual feedback followed by terminal and immediate acoustic feedback.

Developments in technology and information technology (IT) have enabled the development of new techniques for gait re-training based on feedback supplied by electronic devices. This has been demonstrated by authors such as Druzbicki et al. [5], Basta et al. [9], Zanoto et al. [10] and Segal et al. [11].
The basic principle of feedback is the ability to voluntarily control and change certain bodily functions or biological processes when information is provided about them [12]. The main advantage of feedback is the supply of information about a specific biological process about which the patient does not consciously have information [13]. Table 1. Mesh and Decs Terms put into groups by mean.

Terms and Strategies Identifier
feedback or biofeedback or neurofeedback or proprioception 1 treatment or program * or exercise * or rehabilit * or training or educat * or "stimulation training" or teaching or learning 2 software or program * or technology or "biomedical technology" or system 3 gait or walking or ambulation or locomotion or "stair navigation" 4 Randomiza * or study or "clinical trial" 5 Trata * or program * or rehabilit * 6 feedback or biofeedback or neurofeedback or retroalimentación 7 marcha or ambul * or locomoción 8

Database Search Strategy Simplified Strategy
PubMed (treatment or program * or exercise * or rehabilit * or training or educat * or "stimulation training" or teaching or learning) and (feedback or biofeedback or neurofeedback or proprioception) and (gait or walking or ambulation or locomotion or "stair navigation") and (software or program * or technology or "biomedical technology" or system) 2 and 1 and 4 and 3 PEDro feedback and gait 1 and 4 WOS (feedback or biofeedback or neurofeedback or proprioception) and (gait or walking or ambulation or locomotion or "stair navigation") and (software or program * or technology or "biomedical technology" or system) and (randomiza * or study or "clinical trial") 1 and 4 and 3 and 5 CINAHL (feedback or biofeedback or neurofeedback or proprioception) and (gait or walking or ambulation or locomotion or "stair navigation") 1 and 4 Dialnet (trata * or program * or rehabilit *)and (feedback or biofeedback or neurofeedback or retroalimentación) and (marcha or ambul * or locomoción) 6 and 7 and 8

Study Selection and Inclusion Criteria
The papers included in this review had to meet the following criteria: -Population: Mainly patients with a modified or abnormal gait (i.e., spatiotemporal gait parameters) due to a pathology such as cerebral palsy, hip orthoprosthesis, lower member amputation, knee ligamentoplasty, etc. -Interventions: application of technology-based feedback (haptic and/or visual and/or acoustic) to assist functional gait recovery as much as possible. The feedback had to be received by the patient directly (external feedback). -Comparisons: Any comparison between different kinds of feedback (visual, haptic, immediate/concurrent, retarded/terminal, etc.) applied using technology. Or any comparison between technological and non-technological feedback, usual care or an alternative exercise therapy/intervention not based on feedback. -Outcomes: Any validated measures of parameters or aspects associated to gait, such as: pain, functionality, balance, unload weight bearing, spatiotemporal parameters (speed, cadence, step length), kinematic data (range of movement-ROM) and score by specific gait assessment test or scale (i.e., Up and Go, chair-stand time). -Study design: Randomised controlled trials (RCTs). - Measure of methodological quality of RCT: A minimum of 4 points according to PEDro Scale. That is, "fair" and "high" quality studies [32] (see Quality Appraisal). -Language: Studies reported in English or Spanish. -Setting: Not limited to a particular setting.
The titles and abstracts of the search results were screened to check if a study met the pre-established inclusion criteria. We obtained the full text article of those studies which met the criteria, and documented the causes for any exclusions at this stage.

Data Extraction
Data extraction was carried out by one reviewer (A.J.M.) and checked for accuracy by a second reviewer (G.C.M.), using a table designed to detail information on study features, participant characteristics, feedback modality, technology employed (for feedback and assessment), interventions, comparisons, and outcome measurements.
Apposite studies were assessed for methodological quality using the Physiotherapy Evidence Database (PEDro) critical appraisal tool [33]. This method was valid and reliable for assessing the internal validity of a study (criteria [2][3][4][5][6][7][8][9]. We also evaluated the adequacy of the statistical information for interpreting the results (criteria [10][11] [34][35][36]. PEDro consists of 11 criteria overall; although criterion 1 refers to the external validity of the trial and is not included in the final score [34]. Each criterion could be Yes (one point) or No (0 points), with a maximum score out of ten. Only "fair" (scores 4/5) and "high" (scores ≥ 6/10) quality studies [32] were included in this review.

Search Results
We found 884 articles in the electronic databases. Most of them in Pubmed (404), and the rest in PEDro (61), WOS (16), Cinahl (339) and Dialnet (64). Following the removal of duplicates, 776 articles were screened by title, abstract and full-text, due to: not including feedback technology, not applying the feedback directly to the patient, not being RCT, not using feedback for gait functional recovery, not having ≥4 score in PEDro Scale. After the screening, 20 studies were left for inclusion in this review. Figure 1 shows the search and study selection process, which was based on PRISMA [37] guidelines.

Characteristics of Included Studies
A detailed summary of the features and results of each selected study is shown in Table 3.

Characteristics of Included Studies
A detailed summary of the features and results of each selected study is shown in Table 3.      Pedography (Colored graphs simulating foot placement) + emed-q100 pressure platform with 6080 sensors over a sensor area of 475 × 320 mm 2 [21] To examine the effects of auditory feedback during gait on the weight bearing of patients with hemiplegia resulting from a stroke N = 25 Sex = 6 female (24%); 19 male (76%) Age = 57.7 ± 10.75 years Inclusion criteria: Stroke minimum 6 months previously, mini-mental test ≥ 24, walk autonmously at least 10 m unassisted, no orthopedic aids Exclusion criteria: Not specified Pressure meter Ped-AlertTM120 (ORBITEC, Madison, WI, USA)/Acoustic descriptive and terminal (KR) Assessment Technology: GAITRite (CIR Systems Inc, Franklin, NJ, USA) + software GAITRite GOLD, version 3.2b CG (n = 13): walk on GAITrite without feedback + treatment of neurodevelopment IG (n = 12): idem + acoustic feedback (a beep every time 50% of the patient's body weight was exceeded on the paretic leg) Frequency and duration: the training period was a total of 4 weeks Pre-test vs. Post-test Significant and effective: Duration of the Stance Phase (%), Duration of the Single Limb Stance (%), TUG test (sec) Not significant: None  [14] To examine whether gait training with a gait-assistance robot (GAR) improves gait disturbances in subacute nonambulatory hemiplegic stroke patients more than over-ground conventional gait training N = 26 Sex = 6 female (23.1%); 20 male (76.9%) Age = 63.65 ± 9.8 years Inclusion criteria: first stroke less than five weeks prior to the study, unilateral hemispheric brain damage confirmed by computed tomography (CT) or magnetic resonance imaging (MRI), age 40-85 years, serious palsy of lower limbs (level III), Functional Ambulation Classification (FAC) ≤ 2, autonomous gait before stroke, informed consent Exclusion criteria: height < 145 cm or > 180 cm, body weight ≥ 100 kg, marked limitation in ROM of lower limbs, cardiovascular, respiratory, kidney or muscular-skeletal illnesses, difficult communication Load sensors inserted between the sole of the foot and the foot bed of the shoe (the visual feedback regarding the stance phase and load amount)/Visual prescriptive and concurrent (KR) a GAR (Gait-assisted robot) a Treadmill Overground conventional gait training group (OCGT) (n = 13): physiotherapeutic treatment (ROM and muscle strengthening exercises), speech therapy and occupational therapy + OCGT therapy (gait with parallel bars with orthesis of knee-ankle) and gait without parallel bars using forearm crutches) GAR-assisted gait training group (GAGT) (n = 13): idem (except OCGT) + GAGT therapy (lights for the foot pressure biofeedback system). Frequency and duration: 5 days per week for 4 weeks. Session of 60´for physiotherapy, 60´for speech therapy and 60´for occupational therapy and 20f or GAGT or OCGT therapies

Quality Assessment
The results of the PEDro scoring are shown in Table 4. All the selected papers rated "fair" and "high" quality (≥4 points).         Criteria: 1 Eligibility criteria were specified (not used for score); 2 Subjects were randomly allocated to groups; 3 Allocation was concealed; 4 Groups were similar at baseline regarding the most important prognostic indicators; 5 There was blinding of all subjects; 6 There was blinding of all therapists who administered the therapy; 7 There was blinding of all assessors who measured at least one key outcome; 8 Measures of at least one key outcome were obtained from more than 85% of the subjects initially allocated to groups; 9 All subjects for whom outcome measures were available received the treatment or control condition as allocated or, where this was not the case, data for at least one key outcome was analyzed by 'intention-to-treat'; 10 The results of between-group statistical comparisons are reported for at least one key outcome; 11 The study provides both point measures and measures of variability for at least one key outcome). The item "Subjects were randomly allocated to groups" (2) was scored by all papers because it was an inclusion criterion. Besides, the items "Eligibility criteria were specified" (1) and "The results of between-group statistical comparisons are reported for at least one key outcome" (10) were scored in all studies apart from 2.

USV Symbol Macro(s) Description
Although the studies were considered to be of "fair" and "high" quality, there were two items with 0 scores: "Blinding of all subjects" (5) and "Blinding of all therapists who administered the therapy" (6).
All participants were adults bar one [17].

Feedback Technology
Four studies [10,[14][15][16] stood out due to their use of exoskeletons, although only 2 of them produced feedback, Alex II [10] and Lokomat [16]. The others used complementary technology which only assists gait: Gar [14] and Lokomat [15] in this case without feedback.

Feedback Technology
Four studies [10,[14][15][16] stood out due to their use of exoskeletons, although only 2 of them produced feedback, Alex II [10] and Lokomat [16]. The others used complementary technology which only assists gait: Gar [14] and Lokomat [15] in this case without feedback.

Feedback Modalities
The studies used different types of feedback: visual, acoustic and haptic; terminal/retarded and concurrent/immediate; descriptive and prescriptive; with both KR and KP. Visual feedback was used in 60% of the papers, acoustic in 40% and haptic in 15%. Terminal/retarded feedback was used in 55% and concurrent/immediate in 65%. Descriptive feedback was used in 50% of cases, with prescriptive in 60%. KP was featured in 45% and KR in 70% (Table 5).

Feedback Modalities
The studies used different types of feedback: visual, acoustic and haptic; terminal/retarded and concurrent/immediate; descriptive and prescriptive; with both KR and KP. Visual feedback was used in 60% of the papers, acoustic in 40% and haptic in 15%. Terminal/retarded feedback was used in 55% and concurrent/immediate in 65%. Descriptive feedback was used in 50% of cases, with prescriptive in 60%. KP was featured in 45% and KR in 70% ( Table 5).

Discussion
The aim of this review was to synthesize clinical findings regarding the effectiveness of technological feedback in assisting functional gait recovery. Studies defending such effectiveness versus non-technological feedback include: Baram et al. [17], Ki et al. [21], El-Tamawy et al. [23] and Sungkarat et al. [41] amongst others. The authors of this study defend the use of technological feedback but not at the cost of usual care such as: mirror therapy [7], assisted gait [7] or verbal feedback [19], etc. In other words, technological feedback and traditional physiotherapy complement each other in assisting the functional recovery of the patient. To a lesser degree, other authors such as Brasileiro et al. [18], Byl et al. [19] or Hunt et al. [20], state that technological feedback did not obtain positive, or at least significant, results, in relation to other treatments.
In Physiotherapy, the current trend is to improve treatments using new technologies adapted as much as possible to the user needs. Furthermore, it is not only the system that must be individualized, but also the type of feedback used. To exemplify this trend, consider the GCH Control System [27], an instrumented forearm crutch that controls the loads exerted on the crutch when the patient has to partially discharge his/her affected limb. It includes a feedback mechanism to send information about these loads to both the physiotherapist and the patient. When the patient has deficiencies in their coordination skills, the first sessions are usually started with indirect feedback. That is, the therapist receives feedback from the system and verbalizes it to the patient. The patient finds it easier to understand the information through the physiotherapist, who verbally adapts it to their individual conditions (e.g., "Load a little more", "Try to keep that same load", "Be careful that you load more with the right stick than with the left", etc.). The system also has the possibility of adapting the type of feedback (immediate, delayed, visual, auditory, etc.) according to the user's needs. For instance, based on our experience, the use of immediate feedback is easier for the patient and leads to a faster but less lasting result, so it is used when the patient has fewer skills. The delayed feedback is, on the contrary, more complex for the patient and the results come later, although they are more durable [43]. On the other hand, in the case of the GCH System the visual feedback is much simpler than the auditory feedback, which can only be used when the user completely dominates the former.
The articles analyzed in this review highlight how the feedback used when the subject is healthy is more complex [10,22] than when he/she is sick [7,15,17]. Also, in the present review, it is observed how there are parameters such as the cadence that can be easily corrected by means of a sound signal such as that emitted by a digital metronome or a more complex one by means of an exoskeleton [15,21,41]. On the other hand, deviations from the center of gravity are better worked by means of images [11,25].
However, it is worth mentioning that, again according to our experience, current technological systems have the tendency to personalize their treatments but without even nuancing the exact needs of the patient. It will be the therapist who makes the decision to use the technology in one way or another, always based on an initial and continuous assessment of the process and taking into consideration the coordinating, proprioceptive abilities of the user. The feedback received by the therapist for decision-making will be not only through technological means, but also through observational analysis. Both assessments, the technological and the visual or manual, are again complementary in the process of functional recovery of gait.
The technological devices, based on feedback, used by the different authors range from the complex to the basic. The complex group would include, for example: Biodex [5,18], Gaitway [11], GAR [14] or LOKOMAT [15]. The specific characteristics of each device means they each have pros and contras in terms of functionality. For example, LOKOMAT requires much more preparation time than GAR [14]. The basic devices include: heel switches [23], virtual glasses (used as computer monitor) and headphones [17], or a cane with a step-counting sensor [7]. The latter has been rendered obsolete as it has been superseded by other canes [27,44] with much more advanced technology and functions. These devices even have their own software designed specifically for functional gait recovery [27].
On the other hand, the high cost of these devices means that their everyday use is unfeasible despite their effectiveness [20]. Many authors [10,20,26], including those writing this article, favour efficiency versus the effectiveness of clinical technology in relation to financial, spatiotemporal and human resources [45]. In other words, clinical professionals require assessment and treatment systems which are feasible for everyday clinical practice, allowing adequate development of a process of functional [1,22] gait recovery. For instance, Quinzaños et al. [15] highlight the efficacy of the acoustic stimulus for re-training gait cadence and symmetry. As a result, a basic metronome [18] can be highly useful for functional gait recovery.
As this paper's introduction shows, there are many different classifications of feedback. For example, depending on the sense used, it will be acoustic, visual or haptic [28]. Relating to the moment of the stimulus, there is immediate/concurrent or retarded/terminal feedback. Finally, if the information provides data about performance or result we would be talking about KP or KR [30]. The results of this review show that authors do not just use one isolated type of feedback, instead they sometimes prefer to combine them. The one used most on its own is visual feedback [5,10,11,14,[16][17][18][19][20]39,40,42], which is also concurrent [5,10,11,14,[16][17][18][19][20]23,38,40,42]. In contrast, combined, we find four articles with visual and acoustic feedback at the same time [5,10,17,38]: prescriptive and again concurrent visual feedback; and descriptive, concurrent or terminal, acoustic feedback. Summing up, of the RCTs selected in this review, 55% of the articles featured prescriptive and concurrent visual feedback [5,10,11,14,[16][17][18][19][20]40,42], and 30% descriptive and terminal acoustic feedback [5,7,10,15,17,21,41]. Although many of the devices used in the clinical trials had more types of feedback available (for example, haptic [23,26]), the authors opted for concurrent feedback, either terminal acoustic or concurrent visual which are the most effective according to Agresta et al. [6].
Thus, it has been demonstrated that concurrent feedback produces the best short-term results [24], while retarded feedback obtains the best results in the long-term [46,47]. However, other authors such as Parker et al. [24] or Salmoni et al. [48] stress that feedback can be counterproductive for learning a complex task if the procedure is applied in too detailed a manner. In other words, detailed feedback can make it more difficult for the participant to understand or process other sensory information.
We must clarify that this statement refers especially to short-term learning, particularly if complex information is offered to patients with limited coordination skills. If we consider a long-term learning the patient has more time to assume complex information although the authors of this study advocate the progression in difficulty based on a continuous assessment of the process. Another handicap of complex and prolonged feedback is the creation of the patient's dependence on receiving feedback. In this sense, the patient responds to feedback automatically in a specific task but does not integrate the learning so it is unable to extrapolate it to other similar tasks [49].
On the other hand, all the information received by the patient can be descriptive (it simply states and describes the error) or prescriptive (it provides data on how to correct the error) [24]. When the correction is simple like in the aforementioned case of the instrumented forearm crutch, just by describing the load exerted the patient knows that he/she must exert more or less force. In other cases, the description and prescription of the correction are not so obvious. When a patient touches the ground with the foot in the swing phase of a step, the correction depends on the cause and this is multifactorial (kinematics, poor coordination, etc.). The patient may not flex the hip, knee or ankle sufficiently, either due to joint limitation or muscle weakness of the tibialis anterior in the case of dorsiflexion of the ankle, hamstrings for knee flexion or iliopsoas and anterior rectus of the quadriceps in the case of the hip. Another cause would be the lack of proprioception of the patient that prevents her/him from making the gesture or even carrying it out simultaneously (step and triple flexion of the lower limb at a time). In this case, the prescription must be offered by the physiotherapist based on the causes, in a progressive and individualized manner. Selective muscle strengthening exercises, manual therapy to gain range of motion in some joint or working the patient's balance independently to the walking session may be prescribed.
Another example is arm movement during gait. Error detection and description can be easily implemented using technology. On the contrary, the prescription for its correction is usually more complex because again the causes are multiple: lack of integration of the arms in the body scheme, lack of dissociation between the scapular and pelvic waists, lack of mobility of the glenohumeral joint, etc. Deepening further, the patient can brace but not fluidly, i.e., without rotation of the shoulder girdle and without transferring the energy from proximal (trunk) to distal (arms), which would be incorrect. Even the patient may not swing arms in an opposing direction with respect to the lower limb, which would lead to an erroneous walking. Again the prescription must be made by the physiotherapist based on the cause and of course on a rigorous initial and continuous assessment.
Other authors such as Sigrist [49] affirm that to provide the idea of a movement, the feedback should be in principle prescriptive. Eventually, when the subject has internalized the action, descriptive feedback may be applied to make the correction more effective. Similarly, Sulzenbruck [50] states that, before the skill is acquired, prescriptive feedback is more effective than descriptive feedback. Still, there are authors such as Ki et al. [21] who use descriptive feedback (a beep to indicate that the weight load has been exceeded in the paretic limb) while others such as Segal et al. [11] opt for prescriptive feedback in his RCT (a graphic representation of the subject by means of a skeleton, on a screen, informs him how the optimal knee movement should be made).
Overall, the selected articles obtained significantly positive results in relation to the use of technological feedback. Even so, it should be noted that some specific parameters were not particularly significant. That is the case of stride speed or time [5,14,17,18,22,40], which can be influenced by complex robotized systems or exoskeletons, treadmills, supports etc., and the focus of the user's attention on other parameters of interest. These show an improvement in overall gait despite not actually increasing speed.
As for the populations covered, most of the technological feedback applications were applied in the neurological field. The results of this review show that 75% came from that area [5,7,[14][15][16][17][18][19]21,23,[38][39][40][41][42]. Hence, feedback is capable of changing motor strategies in patients with neurological lesions [18], with the application of this type of treatment being more appropriate during early stages of rehabilitation [24]. As for other clinical areas, this review has only included 2 articles (10%) based on muscular-skeletal lesions [11,20]. They outlined the limitation of traditional physiotherapy in the recovery of lower-limb functions [51]. Only 3 articles (15%) used a sample of healthy subjects [10,22,26]. Despite being an RCT, it is sometimes necessary to perform research with healthy subjects to ascertain the efficacy of a new technological system before using it with patients requiring treatment. Continuing with the study population, it should be noted that 95% of the reviewed articles included samples of adult subjects [5,7,10,11,[14][15][16][18][19][20][21][22][23]26,[38][39][40][41][42]. Only 5% of the subjects were under 18 [17]. For this reason, we believe more scientific findings need to be generated in other clinical areas and in young population samples.
As a final reflection, the authors of this study recognize that technological progress has led to the development of highly useful tools in the field of physiotherapy which complement conventional therapy. In no case are these technologies considered substitute media, in contrast to the opinion of Parker et al. [24]. Despite the multiple benefits which new technologies offer, a physiotherapist's face-to-face treatment of a patient cannot be equaled by technological means. The personalized and intuitive adaptation of the health-care professional is the key to successful treatment.

Conclusions
Treatment based on feedback using innovative technology in patients with abnormal gait is mostly effective in improving gait parameters and therefore of use in the functional recovery of a patient. Concurrent/immediate visual is the most frequently used type of feedback, followed by terminal/retarded acoustic. Also, prescriptive feedback and knowledge of result are the most frequent alternatives.
Most of the systems used are based on force and pressure sensors, normally accompanied by complementary software.
Walking speed is the most frequently evaluated parameter, with the majority of studies reporting significant improvements (in one study the changes were only significant after 3 months). The positive effect on the stride length is also found significant in most cases. In general, the number of studies with significant outcomes for the other parameters (such as balance or range of movement) is too low.