A Review of the Plantar Pressure Distribution Effects from Insole Materials and at Different Walking Speeds
by
, ,
Fahni Haris
1,2
,
Ben-Yi Liau
3, 
Yih-Kuen Jan
4,5,6
,
Veit Babak Hamun Akbari
7,
Yanuar Primanda
1,
Kuan-Han Lin
2 and
Chi-Wen Lung
4,7,*
1
School of Nursing, Universitas Muhammadiyah Yogyakarta, Yogyakarta 55183, Indonesia
2
Department of Healthcare Administration, Asia University, Taichung 41354, Taiwan
3
Department of Biomedical Engineering, Hungkuang University, Taichung 433304, Taiwan
4
Rehabilitation Engineering Lab, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
5
Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
6
Computational Science and Engineering, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
7
Department of Creative Product Design, Asia University, Taichung 41354, Taiwan
*
Author to whom correspondence should be addressed.
Appl. Sci. 2021, 11(24), 11851; https://doi.org/10.3390/app112411851
Submission received: 18 November 2021
/
Revised: 8 December 2021
/
Accepted: 9 December 2021
/
Published: 13 December 2021
Abstract
:Featured Application
(A) Walking speeds and insole material are common modulating factors that decrease peak plantar pressure (PPP) in different foot regions; (B) the appropriate walking speed for reducing PPP of the forefoot in DM was slower than non-DM; (C) at a similar walking speed, DM had higher PPP than non-DM; (D) the EVA is more prevalent in investigating reduced PPP in DM compared with other materials; (E) cushioning, resilience, and stiffness may be the essential mechanical properties in insole material for DM.
Abstract
Among people with diabetes mellitus (DM), the two common strategies for decreasing peak plantar pressure (PPP) to reduce diabetic foot ulcers (DFUs) risks are to modify walking speeds and to change insole materials. This study reviewed the PPP reduction based on various walking speeds and insole materials. The articles were retrieved from four major scientific databases and manual search. We identified 1585 articles, of which 27 articles were selected for full-text analysis. We found that in faster walking speeds, the forefoot PPP was higher (308 kPa) than midfoot (150 kPa) and rearfoot (251 kPa) PPP. The appropriate walking speed for reducing the forefoot PPP was about 6 km/h for non-DM and 4 km/h for DM people. The forefoot PPP in DM people was 185% higher than that of non-DM people. Ethylene–vinyl acetate (EVA) insole material was the most popular material used by experts (26%) in the forefoot and reduced 37% of PPP. In conclusion, the suitable walking speed for DM was slower than for non-DM people, and EVA was the most common insole material used to decrease the PPP under the forefoot. The clinicians might recommend DM people to walk at 4 km/h and wear EVA insole material to minimize the DFUs.
1. Introduction
The prevalence of diabetes mellitus (DM) has been reported to increase every year. Uncontrolled DM will increase morbidity, mortality, and economic burdens [1]. The prevalence of DM in 2019 was expected to be 463 million people, growing to 10.2% (578 million people) by 2030 and 10.9% (700 million people) by 2045 [2]. One of DM complications is diabetic foot ulcers (DFUs). It was predicted that one-third of people with DM will experience DFUs in their lives [3,4] and will develop recurrent ulcers about 0.4 times in the first year [5]. Furthermore, the risk of DFUs will increase 3 times for those who have DM more than 10 years, 7 times higher for those who have a level of glycated hemoglobin (HbA1c) above 86 mmol/mL, and 10 times higher for those who have body mass index (BMI) above 25 kg/m2 [6]. Moreover, the annual health expenses for DM, especially for diabetic foot ulcers treatment, was more than USD 10 billion in the United States [7]. Due to its high costs, DM prevention is a primary concern worldwide.
Exercise plays an essential role in DM prevention [8]. The American Diabetes Association (ADA) [9] advises that people with DM should accomplish adequate exercise to decrease the high levels of HbA1c [10] or excess BMI [11]. Exercise has also demonstrated its importance in maintaining a healthy body weight [11], decreasing the risk of cardiovascular diseases [12], and improving glycemic management [10]. The ADA recommends people with DM engage in vigorous aerobic exercise for at least 75 min per week or perform moderate-intensity aerobic exercise for at least 150 min per week [13]. In addition, people may perform aerobic exercise regularly to improve their health.
Healthcare professionals recommend walking as one aerobic exercise, as it is not limited by race, gender, and age [14]. For nearly four decades, walking has been the most popular exercise in physical activity [15,16,17]. There is a paradigm transformation regarding recommended walking to achieve health, from light–moderate exercise [16] to moderate–vigorous exercise [13]. Several studies have extensively documented that walking increases the incidence of DFUs in people with DM due to increased peak plantar pressure (PPP) [18,19,20]. Moreover, to resolve the increased PPP, several studies confirmed that wearing a proper insole decreases the PPP and thus the risk of DFUs [21,22,23]. However, as walking is performed to improve health, on the other hand, it increases the incidence of DFUs. This presents the need to decrease the PPP in walking exercises for people with DM [24]. As an answer, there are two often used strategies by researchers to decrease the PPP—namely, (1) suitable walking speed [25] and (2) suitable insole material [26].
The PPP in the plantar region may vary at different walking speeds [27]. For example, moving forward at faster walking speeds engages the plantar surface to a pronated position that might increase PPP under the forefoot [28,29]. This condition is believed to be a significant factor in affecting abnormally high PPP and further developing to the DFUs [30]. However, Lung et al. have shown that slower walking speed increases PPP in the forefoot [24]. Thus, one factor contributing to high PPP at slower walking speed was the increased foot-to-floor contact time, leading to increased PPP in the central and medial forefoot region [24,27]. Furthermore, the issue of reducing PPP at the plantar region is essential for DFUs prevention. Therefore, appropriate walking speeds may decrease the PPP for DM subjects under the forefoot, midfoot, and rearfoot [31,32].
The ethylene–vinyl acetate (EVA), Poron, Plastazote, and polyurethane were developed based on their function to reduce the PPP in the plantar region [33,34,35]. The insole has functions such as cushioning, resilience, and stiffness. The EVA has been used as an insole material in different plantar regions (forefoot, midfoot, and rearfoot) [36,37,38]. Single EVA as a foam-based material was excellent for energy absorption to support the rearfoot pressure reduction [39]. In addition, a combination of EVA and Poron used as foam-based insole was reported excellent as arch support and optimizing insole plugs. The insole can be customized by removing the square plugs to reduce the PPP in the forefoot region [40]. Additionally, Plastazote and polyurethane (PU) were identified as suitable materials for pressure distribution in the forefoot and rearfoot of a multi-layer Shore A insole [41]. Moreover, with its resilience, Professional Protective Technology (PPT), which provides the material strength necessary for resisting wear and tear, is reported as a high-pressure absorber to reduce the PPP in the forefoot [42]. However, foam-based Poron insole materials were reported as pressure reduction under the forefoot [43]. Therefore, insole materials are current solutions for managing the plantar region with high PPP to decrease DFUs risk [44].
Suitable walking speed, one of the aerobic exercises, is more popular and advantageous in DM people for DFUs prevention. Yet, walking still has a high risk for DFUs development in different walking speeds and plantar regions. On the other hand, different insole material properties may reduce the PPP in different plantar regions. However, to the best of our knowledge, no study investigates the reduction in PPP based on the plantar region in different walking speeds and different insole materials. Therefore, this study analyzes previous studies on PPP in suitable walking speeds among DM and non-DM people to find the DFUs risk features and evaluate the insole material used for DM people providing different functions for plantar regions.
2. Materials and Methods
We searched for published articles through four databases in April 2021, ProQuest (1983 to 2021), PubMed (1976 to 2021), ScienceDirect (1998 to 2021), and Web of Science (1977 to 2021). Search protocols were made based on search guidelines using the Patient, Intervention, Comparison and Outcome model (PICO) with the search terms: diabetes AND foot AND pressure AND insole AND walking. We performed inclusion criteria and exclusion criteria to answer the research objective. We identified additional studies based on Google Scholar conducted by previous studies [45,46].
The data were processed using the SPSS 22 program. Cohen’s Kappa statistics and percentage agreement were calculated to determine whether the two reviewers agreed with the selected papers [47].
The inclusion criteria for this study were as follows: (1) participants had diabetes aged ≥18 years old or healthy people; (2) studies written in English; (3) type of studies: an experimental study, non-experimental study; (4) types of exposure: had activities wearing insoles; (5) types of outcomes: at least one of walking speed, plantar pressures, plantar pressures reductions, and insole materials. The study’s exclusion criterion was regarding the type of studies—namely, abstract-only publications (symposium, conference, proceeding book), protocols, review papers, systematic reviews, meta-analysis studies, and literature reviews were excluded.
The selection process based on the titles and abstracts of the studies identified in the literature against the inclusion and exclusion criteria was conducted independently by two researchers (F.H. and C.W.L.). Further, they (F.H. and C.W.L.) independently analyzed the selected studies. The agreement between two independent reviewers for screening titles and abstracts (Kappa 0.814, agreement percentage 99.2%), full-text screening (Kappa 0.773, agreement percentage 91.9%). A third researcher (K.H.L.) consulted disagreement between two researchers, who provided the final decision. There was no disagreement on the articles selected for this review.
A matrix table was developed to extract the data from the selected studies. The leading information to be collected was related to the two PPP aspects: (1) plantar pressure distribution at different walking speed selection and (2) insole mechanical properties.
3. Results
3.1. Selected Studies
A total of 1585 papers were found, 1580 from four databases, and five manually identified through other sources using search terms. As many as 1548 studies were included following the elimination of duplicates (n = 37). After reviewing the abstracts, we removed 1511 articles and retrieved 37 papers for full-text analysis. We excluded ten studies; eight studies lacked specific insoles, one discussed artificial intelligence, and one analyzed insole cost effectiveness. We included 27 articles for the final analysis. Figure 1 describes the flow diagram for the selection process of studies included in this review. Figure 2 describes the published paper on PPP reduction strategies.
3.2. The PPP at Different Walking Speeds
Of the 27 studies, 18 investigated the walking speed at which participants felt comfortable. The walking distance among the subjects was allowed to walk in 8–20 m of length with 15–20 steps and was repeated 2–6 times [48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65]. Three studies did not mention the participants’ walking speed, but subjects had to walk to gain the data [66,67,68]. However, Even-Tzur et al. calculated heel pad pressure using a finite element method and did not perform walking intensities [69]—the insole material used by Even-Tzur et al. had EVA viscoelastic properties [69].
The PPP at different walking speeds in non-DM in five studies was integrated into these results. Ryu et al. asked their subjects to walk at 4 km/h and 6 km/h [70], while Burnfield et al. set the walking speed at 6 km/h [71]. Other walking tests were conducted at 8 km/h and 12 km/h [72], 10 km/h [73], and 12 km/h speed [74]. See Table 1 for more detail.
Figure 3 shows the PPP distribution in people with DM and non-DM at different walking speeds [48,55,70,72,73,74]. The mean forefoot PPP at a walking speed of 4 km/h was 185% higher in DM than non-DM people. In addition, the mean PPP under the midfoot and the rearfoot were 135% and 124%, respectively, greater among DM people. However, among non-DM, we found that the lowest PPP at the three regions was achieved at a walking speed of 6 km/h. The PPP at 6 km/h walking speed was lower than at 4 km/h, 66% under the forefoot, 57% under the midfoot, and 78% under the rearfoot. On the other hand, the PPP at 8 km/h walking speed was remarkably higher than at 4 km/h was 236% under the forefoot, 224% under the midfoot, and 123% under the rearfoot.
3.3. Insole Materials Used in Various Regions
Figure 4 illustrates the insole materials that have been prescribed in three regions in people with DM [48,49,50,51,52,53,54,55,56,57,59,60,61,62,63,64,65,66,67,68]. The most common insole materials used at the forefoot regions were EVA (26%), followed by Poron (13%), Plastazote (11%), PU (9%), PPT (5%), and others (36%). Similarly, insole materials used at the midfoot and rearfoot region were EVA (26% and 27%, respectively), followed by Poron, Plastazote, PU, PPT, and others. See the detail of each insole material used for DM people based on the reviewed studies (Table 2, Table 3 and Table 4). Four studies found that the average PPP reduction using EVA insole material was 38% on the whole foot and 37% on the forefoot region (Table 5).
3.4. Insole Mechanical Properties
Chatzistergos et al. used polyurethane foam as an insole with a mechanical stiffness ranging from 35 kPa to 350 kPa, and from 2 to 20 Shore A. The pressure reduction was around 5–29% in walking speed ranging between 4.3 km/h and 5.8 km/h (Figure 5A) [58]. The insole material was 3D printed in thermoplastic polyurethane conducted by Chatzistergos et al. (2020), formed at different densities (10–20%), with the stiffness ranging from 110 kPa to 350 kPa with pressure reduction ranging from 20% to 38% at selected walking speeds (Figure 5B) [62]. Even et al. used EVA in a finite element study to predict a reduction of 2 kPa with 10% thickness and 8 kPa with 50% thickness on peak heel pad stress compared to without EVA. The peak heel pad stress was predicted to be reduced by 13.5 kPa (125% of insole elastic modulus) and 13 kPa (150% of insole elastic modulus) (Figure 5C) [69]. Table 6 describes the material of the insole based on their character and function used in plantar regions.
4. Discussion
This study analyzed the available data on the PPP effect at different walking speeds and various insole materials in healthy people and people with DM. Our results have important implications that the appropriate walking speed for healthy people was around 6 km/h. In contrast, an appropriate walking speed for DM people was around 4 km/h. Moreover, the forefoot pressure at 4 km/h walking speed in people with DM was nearly two times higher than that for non-DM people. The EVA was the most often used insole material for walking at the forefoot region (26%). EVA reduced the PPP by 37% on the DM forefoot region.
Our results showed that 6 km/h was the appropriate walking speed for non-DM, with the lowest PPP in the forefoot, midfoot, and rearfoot regions (Figure 2). McClymont et al. demonstrated that when walking faster, the mean square error, one of the variability metrics of plantar pressures, increased considerably [75]. Elevated plantar pressures may accumulate tension abnormally over the plantar soft tissue [76]. Therefore, to reach the lowest PPP, DM people and non-DM may have different suitable walking speeds [31,32,77]. Non-DM appropriate walking speed was closely correlated with the neutral subtalar joint position, neither pronated nor supinated, which may reduce PPP [78]. Moreover, a walking speed above 6 km/h in non-DM has a high PPP on the forefoot region (Figure 2). Martinez et al. stated that ankle joint position changed into high pronation during faster walking [79]. The transformation into a pronated position at faster walking speeds might be due to muscle fatigue-inducing high pressure under the forefoot [28,29]. In addition, a walking speed of less than 6 km/h showed increased PPP on the heel (Figure 2). One reason why the rearfoot region has a high PPP may be founded on the increased contact time of slow walking due to severe internal distortion between bone and soft tissue [80].
The study concluded that the forefoot PPP at 4 km/h walking speed was nearly two times (185%) higher in DM people than non-DM people (Figure 2). The high PPP at 4 km/h walking speed may have three reasons: increased contact time, ankle joint stiffness, and soft tissue stiffness. First, DM people lose ankle movement perception, owing to increasing step time to walk carefully to keep their balance at 4 km/h walking speed [27,81]. Hence, DM people decreased their step length, gained slower walking speeds, and had higher PPP in the forefoot region than non-DM [27,32]. Second, high PPP at 4 km/h walking speed on DM people was due to ankle joint stiffness (severe DM; 0.236 N·m/deg compared with normal DM: −0.113 N·m/deg) [82]. Ankle plantar flexor (equinus) in DM becomes contracture, produced by stiff tissue causes the heel to rise earlier than normal, employing higher pressure on the forefoot [83]. Third, DM people have high PPP at 4 km/h walking speed due to tissue stiffness. Sun et al. demonstrated that soft tissue stiffness in the forefoot of people with DM was around 1.5 times higher (155%) than non-DM [84]. Increases in diabetic soft tissue stiffness may be attributed to the accumulation of cross-linked collagen molecules, which are abundant in soft tissue [85]. Electron microscopy shows evidence of regular collagen alignment loss, increased collagen fibril density, and increased fibril adhesion in patients with DM [86,87].
This study revealed that the most commonly used insole material in the forefoot was EVA (26%). EVA decreased the forefoot pressure by about 37% during walking in people with DM (Figure 3 and Table 5). The EVA insole, a foam-based material that provides high resilience, is excellent for reusing mechanical energy at the forefoot on the push-off phase during walking [44,88,89]. The typical rebound resilience of polyethylene foam ranged from about 30% to 40% [90]. In addition, the cushioning function of the insole provides extra resilience to the EVA insole material. Kwon et al. stated that when the resilience of EVA reached 63%, the insole was softer compared with 17% that was stiffer [91]. Furthermore, the Australian Diabetic Association suggested that DM people wear soft but sufficiently resilient insole because it redistributes plantar pressure and increases contact time between the foot and insole [22]. It means that EVA materials might be excellent in reusing mechanical energy by adjusting greater resilience [92].
Aside from EVA, PU is a good insole material for pressure reduction in the forefoot [43]. This study discovered that the mechanical properties of the PU insole have almost the same PPP reduction as EVA (37%) (Figure 4B). The mechanical properties of the PU insole reduced the pressure by around 30% at 14 Shore A and about 40% in 10–16% 3D printing infill density. Cushioning and stiffness optimization of the PU insole has been approved for decreasing the PPP in the forefoot [58,62]. Some researchers argued that PU has some advantages in its mechanical properties [93,94]. Nonetheless, PU is more expensive than EVA [93,95,96]. Thus, PU could be the multi-insole in part of the plantar region combined with another insole material [41,97].
This study has two limitations. First, our study was limited to discussing EVA and PU in pressure reduction but not in Plastazote and Poron as the second and third most commonly used insole materials. Only a few researchers examined Plastazote and Poron because they need longer walking duration to induce pressure reduction. For example, after a month of use, a single Plastazote has the pressure reduction result [98], and Poron has the pressure reduction after 50,000 steps [43]. If four insole materials are compared in the same procedure, the results may show different PPP reductions. Thus, the walking duration effect to induce pressure reduction should be conducted in further studies. Second, our study focused on the three regions of PPP reduction in walking speeds and insole materials—forefoot, midfoot, and rearfoot. Since the first and second metatarsal heads in the forefoot medial region change pronated positions, alongside the three regions in this study, DFUs may occur in other smaller regions. Due to other smaller regions being at high risk for DFUs, future work may be arranged to investigate the other foot regions such as the first toe.
5. Conclusions
This study is essential in better understanding the insole materials that improve PPP reduction in various walking speeds in people with DM. We established that the appropriate walking speed for non-DM people is 6 km/h. Four km/h is the appropriate walking speed for DM people, with 185% forefoot pressure higher than non-DM. The EVA is the most commonly used material with 37% forefoot pressure reduction. Therefore, the clinician may recommend people with DM to walk at an appropriate speed and wear proper insole material to minimize the DFUs risk.
Author Contributions
Conceptualization, F.H. and C.-W.L.; methodology, F.H. and C.-W.L.; validation, B.-Y.L., Y.P., and K.-H.L.; investigation, F.H. and C.-W.L.; writing—original draft preparation, F.H. and C.-W.L.; writing—review and editing, Y.P., V.B.H.A., B.-Y.L., and Y.-K.J.; supervision, Y.-K.J. and C.-W.L.; funding acquisition, C.-W.L. All authors have read and agreed to the published version of the manuscript.
Funding
This study was funded by the Ministry of Science and Technology of the Republic of China (MOST-110-2221-E-468-005, MOST-110-2813-C-468-134-E, and MOST-110-2637-E-241-002). The funding agency did not have any involvement in data collection, data analysis, and data interpretation.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Informed consent was obtained from all subjects involved in the study.
Data Availability Statement
The dataset used for analysis during the current study are available from the corresponding author on reasonable request.
Acknowledgments
The authors wish to express gratitude to Ferry Fadzlul Rahman for the assistance.
Conflicts of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Figure 1.
Flow diagram for study selection.
Figure 2.
Published paper for reduction peak plantar pressure strategies. DM, diabetes mellitus; non-DM, healthy people; EVA, ethylene–vinyl acetate.
Figure 2.
Published paper for reduction peak plantar pressure strategies. DM, diabetes mellitus; non-DM, healthy people; EVA, ethylene–vinyl acetate.
Figure 3.
The PPP at three regions (A) forefoot, (B) midfoot, and (C) rearfoot. The speed was categorized as preferred walking speed in people with DM (4 km/h) and five different speeds in non-DM people (4, 6, 8, 10, and 12 km/h, respectively). PPP, peak plantar pressure; DM, diabetes mellitus; non-DM, healthy people.
Figure 3.
The PPP at three regions (A) forefoot, (B) midfoot, and (C) rearfoot. The speed was categorized as preferred walking speed in people with DM (4 km/h) and five different speeds in non-DM people (4, 6, 8, 10, and 12 km/h, respectively). PPP, peak plantar pressure; DM, diabetes mellitus; non-DM, healthy people.
Figure 4.
Published paper used insole material under plantar area: (A) forefoot, (B) midfoot, and (C) rearfoot. EVA, ethylene–vinyl acetate; PU, polyurethane; PPT, Professional Protective Technology. The percentage of insole used in the foot region is based on “summary” divided by the total insole used. The term “other” summarizes 11–13 items that do not represent the most used insole material.
Figure 4.
Published paper used insole material under plantar area: (A) forefoot, (B) midfoot, and (C) rearfoot. EVA, ethylene–vinyl acetate; PU, polyurethane; PPT, Professional Protective Technology. The percentage of insole used in the foot region is based on “summary” divided by the total insole used. The term “other” summarizes 11–13 items that do not represent the most used insole material.
Figure 5.
Pressure reduction in different insole material properties: (A) PU foam, (B) 3D-printed thermoplastic PU, and (C) EVA. PU, polyurethane; 3D, three dimensions; EVA, ethylene–vinyl acetate.
Figure 5.
Pressure reduction in different insole material properties: (A) PU foam, (B) 3D-printed thermoplastic PU, and (C) EVA. PU, polyurethane; 3D, three dimensions; EVA, ethylene–vinyl acetate.
Table 1.
The peak plantar pressure in preferred walking speed in people with DM and different walking speeds in non-DM people.
Table 1.
The peak plantar pressure in preferred walking speed in people with DM and different walking speeds in non-DM people.
| Region | Clinical Finding (Reference) | Walking Speed | |||||
|---|---|---|---|---|---|---|---|
| DM | Non-DM | ||||||
| 4 km/h | 4 km/h | 6 km/h | 8 km/h | 10 km/h | 12 km/h | ||
| Forefoot (kPa) |
| 217 | -- | -- | -- | -- | -- |
| 221 | 183 | -- | -- | -- | -- | |
| -- | 53 | 46 | -- | -- | -- | |
| -- | -- | -- | 278 | -- | 302 | |
| -- | -- | -- | -- | 261 | -- | |
| -- | -- | -- | -- | -- | 315 | |
| -- | -- | 110 | -- | -- | -- | |
| Mean | 219 | 118 | 78 | 278 | 261 | 308.5 | |
| Midfoot (kPa) |
| 95 | -- | -- | -- | -- | -- |
| 100 | 116 | -- | -- | -- | -- | |
| -- | 28 | 32 | -- | -- | -- | |
| -- | -- | -- | 161 | -- | 177 | |
| -- | -- | -- | -- | 150 | -- | |
| -- | -- | -- | -- | -- | 124 | |
| -- | -- | 50 | -- | -- | 124 | |
| Mean | 97.5 | 72 | 41 | 161 | 150 | 150.5 | |
| Rearfoot (kPa) |
| 171 | -- | -- | -- | -- | -- |
| 256 | 240 | -- | -- | -- | -- | |
| -- | 104 | 128 | -- | -- | -- | |
| -- | -- | -- | 212 | -- | 199 | |
| -- | -- | -- | -- | 216 | -- | |
| -- | -- | -- | -- | -- | 303 | |
| -- | -- | 140 | -- | -- | 124 | |
| Mean | 213.5 | 172 | 134 | 212 | 216 | 251 | |
Note: DM, diabetes mellitus; km/h, speed units.
Table 2.
The published paper discussed selected insole materials on the forefoot region.
| Clinical Finding (Reference) | EVA | Poron | Plastazote | PU | PPT | Other |
|---|---|---|---|---|---|---|
| -- | 1 | 1 | -- | -- | -- |
| 1 | -- | -- | -- | -- | 2 |
| 1 | -- | -- | -- | -- | 5 |
| -- | 1 | 1 | 1 | -- | |
| 1 | 1 | -- | -- | -- | 1 |
| -- | -- | -- | 1 | -- | |
| 1 | -- | -- | 1 | -- | 2 |
| 1 | -- | -- | -- | -- | 1 |
| 1 | 1 | -- | -- | -- | -- |
| 1 | -- | -- | -- | 1 | -- |
| -- | -- | -- | -- | -- | 3 |
| -- | -- | 1 | -- | -- | 1 |
| 1 | 1 | 1 | -- | -- | 1 |
| 1 | 1 | -- | -- | -- | -- |
| 1 | 1 | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | 1 |
| 1 | -- | -- | -- | -- | -- |
| 1 | -- | -- | 1 | -- | 1 |
| 1 | -- | 1 | -- | 1 | 1 |
| 1 | -- | 1 | 1 | 1 | 1 |
| Summary | 14 | 7 | 6 | 5 | 3 | 20 |
| Percentage | 26% | 13% | 11% | 9% | 5% | 36% |
Note: DM, diabetes mellitus; DFUs, diabetic foot ulcers; PPP, peak plantar pressure; EVA, ethylene–vinyl acetate; PU, polyurethane; PPT, Professional Protective Technology.
Table 3.
The published paper discussed selected insole materials on the midfoot region.
| Clinical Finding (Reference) | EVA | Poron | Plastazote | PU | PPT | Other |
|---|---|---|---|---|---|---|
| 1 | -- | -- | -- | -- | 2 |
| 1 | -- | -- | -- | -- | 5 |
| -- | 1 | 1 | 1 | -- | -- |
| 1 | 1 | -- | -- | -- | 1 |
| -- | -- | -- | 1 | -- | -- |
| 1 | -- | -- | 1 | -- | -- |
| 1 | -- | -- | -- | -- | 1 |
| 1 | -- | -- | -- | -- | -- |
| 1 | -- | -- | -- | 1 | -- |
| -- | -- | -- | -- | -- | 3 |
| -- | -- | 1 | -- | -- | 2 |
| 1 | 1 | 1 | -- | -- | 1 |
| 1 | 1 | -- | -- | -- | -- |
| 1 | 1 | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | 1 |
| 1 | -- | -- | -- | -- | -- |
| 1 | -- | -- | 1 | -- | 1 |
| 1 | -- | 1 | -- | 1 | 1 |
| 1 | -- | 1 | 1 | 1 | 1 |
| Summary | 14 | 7 | 6 | 5 | 3 | 19 |
| Percentage | 26% | 13% | 11% | 9% | 6% | 35% |
Note: DM, diabetes mellitus; DFUs, diabetic foot ulcers; PPP, peak plantar pressure; EVA, ethylene–vinyl acetate; PU, polyurethane; PPT, Professional Protective Technology.
Table 4.
The published paper discussed selected insole materials on the rearfoot region.
| Clinical Finding (Reference) | EVA | Poron | Plastazote | PU | PPT | Other |
|---|---|---|---|---|---|---|
| 1 | -- | -- | -- | -- | 5 |
| -- | 1 | 1 | 1 | -- | -- |
| 1 | 1 | -- | -- | -- | 1 |
| -- | -- | -- | 1 | -- | -- |
| 1 | -- | -- | 1 | -- | -- |
| 1 | -- | -- | -- | -- | 1 |
| 1 | -- | -- | -- | -- | -- |
| 1 | -- | -- | -- | 1 | -- |
| -- | -- | -- | -- | -- | 3 |
| -- | -- | 1 | -- | -- | 2 |
| 1 | 1 | 1 | -- | -- | 1 |
| 1 | 1 | -- | -- | -- | -- |
| 1 | 1 | -- | -- | -- | -- |
| -- | -- | -- | -- | -- | 1 |
| 1 | -- | -- | -- | -- | -- |
| 1 | -- | -- | 1 | -- | 1 |
| 1 | -- | 1 | -- | 1 | 1 |
| 1 | -- | 1 | 1 | 1 | 1 |
| Summary | 13 | 5 | 5 | 5 | 3 | 17 |
| Percentage | 27% | 10% | 10% | 10% | 7% | 36% |
Note: DM, diabetes mellitus; DFUs, diabetic foot ulcers; PPP, peak plantar pressure; EVA, ethylene–vinyl acetate; PU, polyurethane; PPT, Professional Protective Technology.
Table 5.
EVA insole materials reduce the PPP in the plantar region.
| Clinical Finding (Reference) | Whole Foot Reduced PPP | Forefoot Reduced PPP |
|---|---|---|
| 16% | -- |
| -- | 32% |
| 60% | -- |
| -- | 42% |
| Mean reduced PPP | 38% | 37% |
Note: PPP, peak plantar pressure.
Table 6.
Insole materials based on their character and function used in plantar regions.
| Material Form | Combination Material | Character | Plantar Region | Region Function | Reference | |
|---|---|---|---|---|---|---|
| Thickness | Shore | |||||
| EVA | ||||||
| Soft, flat compared to molded | PPT | EVA (12.7 mm) PPT (1.5 mm) | 40 Shore A (n/a) | WF | Reduce pressure | [65] |
| Soft, shape based | Plastazote | EVA (n/a) Plastazote (n/a) | 45 Shore A (n/a) | WF | Reduce pressure | [51] |
| Soft, shape based | Poron | EVA (n/a) Poron (n/a) | 35 Shore A (n/a) | WF | Reduce pressure | [51] |
| Extra deep, medium density | Poron | EVA (n/a) Poron (n/a) | (n/a) (n/a) | WF | Insole durability | [67] |
| Extra deep, Soft, and flexible | Poron | EVA (3 mm) Poron (3 mm) | 50 Shore A 25 Shore A | WF | Reduce PPP | [48] |
| Flat, covered soft Poron | Poron | EVA (3 mm) Poron (3 mm) | 50 Shore A 25 Shore A | MTH, RF | Reduce PPP | [48] |
| Elastic | EVA | EVA (n/a) EVA (n/a) | 30 Shore A 50 Shore A | WF | PPP distribution | [61] |
| Molded, MTH bar | (n/a) | (n/a) | 35 Shore A | MTH, MF, RF | Reduce pressure | [55] |
| Molded, MTH bar | (n/a) | (n/a) | 55 Shore A | MTH, MF, RF | Reduce pressure | [55] |
| Soft | EVA, polyethylene | EVA (3 mm) EVA (3 mm) Polyethylene (1.5 mm) | 35 Shore A 45 Shore A 20 Shore A | WF | Decrease shear stress and pressure | [66] |
| Elastic, soft | Silicon, rubbatex, | EVA (n/a) Silicon (n/a) Rubbatex (n/a) | (n/a) (n/a) (n/a) | WF | Frictional resistance | [56] |
| Viscoelastic properties | (n/a) | (n/a) | (n/a) | (n/a) | Estimated PPP reduction | [69] |
| Thick, soft | (n/a) | (n/a) | 50 Shore A | MTH, A | Increase total contact | [63] |
| Thick, soft pad | PPT | EVA (3 mm) PPT (4 mm) | 35 Shore A (n/a) | MTH | Reduce MTH pressure | [63] |
| Soft | EVA | EVA (3 mm) EVA (5 mm) | 20 Shore A 50 Shore A | MTH | Reduce MTH pressure | [59] |
| Cushion | (n/a) | (n/a) | (n/a) | FF, MF, RF | PPP reduction | [74] |
| Flat insole | (n/a) | 5 mm | (n/a) | FF, MF, RF | PPP reduction | [73] |
| Molded insole | arch support | EVA (5 mm) Arch support (n/a) | (n/a) (n/a) | FF, MF, RF, A | PPP reduction | [73] |
| Shock absorber (fusion EVA) | (n/a) | 4–9 mm | (n/a) | FF, H | PPP reduction, comfort | [70] |
| Shock absorber | (n/a) | 4–9.4 mm | (n/a) | FF, H | PPP reduction, comfort | [70] |
| Poron | ||||||
| Soft | EVA, flexible cotton | Poron (4 mm) EVA (4 mm) Flexi cotton (1 mm) | (n/a) (n/a) (n/a) | MTH, RF | Decrease pressure | [54] |
| Soft | EVA | Poron (3 mm) EVA (5 mm) | 20 Shore A 50 Shore A | MTH | Reduce MTH pressure | [59] |
| Plastazote | ||||||
| Total contact, elastic | (n/a) | 10 mm | 35 Shore A | MTH | Redistribute pressure under MTH. | [50] |
| Elastic | Microcellular rubber | Plastazote (8 mm) Microcellular rubber (10 mm) | 25 Shore A 70 Shore A | WF | Reduce pressure | [60] |
| Soft | PPT | Plastazote (n/a) PPT (n/a) | (n/a) (n/a) | WF | Standard insole, pressure resistance | [56] |
| Soft pad | PPT | Plastazote (3 mm) PPT (3 mm) | 25 Shore A (n/a) | MTH | Reduce MTH pressure 30%) | [63] |
| PU | ||||||
| Molded, total contact foam | Combilux Memorix Microvibre | PU 8 mm Combilux 2.3 mm Memorix 3 mm Microvibre 0.7 mm | (n/a) (n/a) (n/a) (n/a) | WF | Pressure redistribution | [52] |
| Lightweight, flexible | (n/a) | 5 mm | (n/a) | WF | Reduce the PPP | [49] |
| Molded, flexible, lightweight | (n/a) | 6 mm | (n/a) | WF | Pressure reduction | [49] |
| Foam and vibrator | vibration devices, merino wool | PU 6–12 mm | (n/a) | FF, A, RF | Reduce the recurrence ulcer (redistribute the pressure) | [64] |
| Soft | (n/a) | (n/a) | (n/a) | WF | Redistribute the pressure | [63] |
| Cushion | (n/a) | 10 mm | (n/a) | WF | Reduce PPP with different density | [62] |
| Various stiffness | (n/a) | (n/a) | (n/a) | WF | Stiffness optimizations reduce PPP | [58] |
| Other | ||||||
| Polyethylene foam (molded, total contact, flexible) | (n/a) | 4 mm | (n/a) | WF | Retain its shape | [50] |
| Cork (cast, elastic) | EVA, Plastazote | Cork (n/a) EVA (n/a) Plastazote (n/a) | (n/a) | MTH | Pressure reduction | [57] |
| Cork (total contact, soft) | Thermoplastic, Plastazote | Cork (n/a) Thermoplastic (n/a) Plastazote (n/a) | (n/a) | MTH | Pressure reduction | [57] |
| Calbino macrofiber (molded) | EVA | Calbino 0.7 mm EVA 4 mm | (n/a) | WF | To reduce PPP | [52] |
| Multi foam (elastic) | Plastazote Microcellular rubber | Multi foam 5 mm Plastazote 8 mm Microcellular rubber 10 mm | 30 Shore A 25 Shore A 70 Shore A | WF | Reduce pressure | [60] |
| Polypropylene shell (thin, molded) | Plastazote | Polypropylene shell (n/a) Plastazote (n/a) | (n/a) | WF | Reduce the PPP | [51] |
| Multicellular rubber (elastic, durable) | (n/a) | 10 mm | (n/a) | WF | Shock absorbent, pressure redistribution | [49] |
| Prefabricated insole (pad and arch support material) | (n/a) | 2 mm | (n/a) | MTH, MF, RF | Reduce pressure | [55] |
| Thin nonstick sheets (grip) | (n/a) | (n/a) | (n/a) | (n/a) | Reduce shear stress | [66] |
| Micro cork (thick molded, elastic) | EVA | Micro cork (5 mm) EVA (n/a) | 35–40 Shore A | WF | Pressure relief | [63] |
| Vacuum insole (cushion dual-density in rocker shoe) | (n/a) | (n/a) | (n/a) | WF | Redistribute pressure in the forefoot | [53] |
| Own shoes | (n/a) | (n/a) | (n/a) | MTH, A, RF, A, T | PPP in walking speed (barefoot and shod) | [71] |
| Fabrication insole (shock absorber) | (n/a) | (n/a) | (n/a) | WF | Mean of PPP and balance | [68] |
| Air insole (cushion) | (n/a) | (n/a) | (n/a) | FF, MF, RF | PPP reduction | [74] |
| Gel (cushion) | (n/a) | (n/a) | (n/a) | FF, MF, RF | PPP reduction | [74] |
| Adiprene (cushion) | (n/a) | (n/a) | (n/a) | FF, MF, RF | PPP reduction | [74] |
| Polyester (traditional army) | viscose fiber, ISOFIX | Polyester (4 mm) Viscose fiber (n/a) ISOFIX (n/a) | (n/a) | FF, MF, RF | PPP reduction | [72] |
| Shock Stop Formthotics (shock absorber) | (n/a) | 15 mm | (n/a) | FF, MF, RF | PPP reduction | [72] |
| Sponge (shock absorber) | (n/a) | 4–9 mm | (n/a) | FF, H | PPP reduction, comfort | [70] |
Note: PPP, peak plantar pressure; T, toes; MTH, metatarsal head; WF, whole foot; FF, forefoot; MF, midfoot; RF, rearfoot; A, arch; EVA, ethylene–vinyl acetate; PPT, Professional Protective Technology; PU, polyurethane; n/a, not applicable.
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Haris, F.; Liau, B.-Y.; Jan, Y.-K.; Akbari, V.B.H.; Primanda, Y.; Lin, K.-H.; Lung, C.-W. A Review of the Plantar Pressure Distribution Effects from Insole Materials and at Different Walking Speeds. Appl. Sci. 2021, 11, 11851. https://doi.org/10.3390/app112411851
AMA Style
Haris F, Liau B-Y, Jan Y-K, Akbari VBH, Primanda Y, Lin K-H, Lung C-W. A Review of the Plantar Pressure Distribution Effects from Insole Materials and at Different Walking Speeds. Applied Sciences. 2021; 11(24):11851. https://doi.org/10.3390/app112411851
Chicago/Turabian StyleHaris, Fahni, Ben-Yi Liau, Yih-Kuen Jan, Veit Babak Hamun Akbari, Yanuar Primanda, Kuan-Han Lin, and Chi-Wen Lung. 2021. "A Review of the Plantar Pressure Distribution Effects from Insole Materials and at Different Walking Speeds" Applied Sciences 11, no. 24: 11851. https://doi.org/10.3390/app112411851
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