The arch support insoles show benefits to people with flatfoot on stance time, cadence, plantar pressure and contact area

Yu-ping Huang; Hsien-Te Peng; Xin Wang; Zong-Rong Chen; Chen-Yi Song

doi:10.1371/journal.pone.0237382

. 2020 Aug 20;15(8):e0237382. doi: 10.1371/journal.pone.0237382

The arch support insoles show benefits to people with flatfoot on stance time, cadence, plantar pressure and contact area

Yu-ping Huang ^1,^2,^#, Hsien-Te Peng ^2,^#, Xin Wang ³, Zong-Rong Chen ^2,⁴, Chen-Yi Song ^5,^*

Editor: Gianluca Vernillo⁶

PMCID: PMC7446821 PMID: 32817709

Abstract

Background

Pes planus (flatfoot) is a common deformity characterized by the midfoot arch collapses during walking. As the midfoot is responsible for shock absorption, persons with flatfoot experience increased risk of injuries such as thumb valgus, tendinitis, plantar fasciitis, metatarsal pain, knee pain, lower-back pain with prolonged uphill, downhill, and level walking, depriving them of the physical and mental health benefits of walking as an exercise.

Methods

Fifteen female college students with flatfoot were recruited. A wireless plantar-pressure system was used to measure the stance time, cadence, plantar pressure, and contact area. Parameters were compared between wearing flat and arch-support insoles using a two-way repeated measures ANOVA with on an incline, decline, and level surface, respectively. The significance level α was set to 0.05. The effect size (ES) was calculated as a measure of the practical relevance of the significance using Cohen’s d.

Results

On the level surface, the stance time in the arch-support insole was significantly shorter than in the flat insole (p<0.05; ES = 0.48). The peak pressure of the big toe in the arch-support insole was significantly greater than in the flat insole on the uphill (p<0.05; ES = 0.53) and level surfaces (p<0.05; ES = 0.71). The peak pressure of the metatarsals 2–4 and the contact area of the midfoot in the arch-support insole were significantly greater than in the flat insole on all surfaces (all p< 0.05).

Conclusions

These results imply that wearing an arch-support insole provides benefits in the shortened stance time and generation of propulsion force to the big toe while walking on uphill and level surfaces and to the metatarsals 2–4 while walking on the level surface. More evenly distributed contact areas across the midfoot may help absorb shock during uphill, downhill and level walking.

Introduction

The foot is an integral component of the human skeletal system and plays an important role in walking. Pes planus (flatfoot) is a very common symptom frequently encountered among many diseases associated with the foot. Previous study has estimated the prevalence of mild and severe cases of the flatfoot to be 16.2% among males and 11.7% among females which was close to each other in gender [1]. Nevertheless, females are more likely to suffer from risks of lower extremity injuries in running [2] and lack of flexible foot/shank coupling coordination compared to males [3]. Approximately 1% of the population suffers from rigid flatfoot, i.e., the arch height of the foot does not change between the weight-bearing and non-weight-bearing states [4, 5]. Many cases are isolated to the period while the skeletal structure is still developing: around 46% of children aged 2 to 6 years but only 14% of those 8 to 13 years suffer from the flexible flatfoot [6].

Flatfoot deformity is related to a lack of foot arch support and insufficient flexibility of the plantar ligaments and tendons [5, 7], and the collapse in the medial arch of the foot [8]. It reduces the ability to absorb the impact on the foot while walking or running [8] and can further increase the risk of foot injury and even lead to thumb valgus, tendinitis, plantar fasciitis, metatarsal pain, knee pain, lower-back pain because of the high impact forces [5, 9–12]. In people with flatfoot, the foot pronation is abnormal or excessive while walking [11–13], leading to increased fatigue in the lower extremities [8], which contributes to increased risk of the lower-extremity injury [14, 15]. As a result, people with flatfoot usually have troubles engaging in prolonged walking or running because of the lack of the load-bearing structure of the foot arch, shock dissipation and stable support of the lower extremity [9].

Foot orthoses can alleviate the symptoms of medial tibial stress [16] and significantly reduce the pain in the lower extremities [17]. They also mitigate the symptoms of lower-back pain [18] and plantar fasciitis [19]. Furthermore, orthopedic insoles demonstrated a 75.5% symptom improvement of excessive leg internal rotation, leg length discrepancy, patellofemoral pain syndrome, and plantar fasciitis symptoms [20]. Arch-support structures are often incorporated into foot orthoses for the flatfoot [17]. Previous studies have shown that arch-support insoles can reduce the peak vertical ground reaction force (GRF) in the heel by 6.9% of the body weight and increase the peak vertical GRF by 7% of the body weight [21]. They also lead to better medial-lateral control of the center of pressure of the foot, provide stability during walking [21], enable faster stair ascent time, and improve basic mobility, physical health, and comfort [17].

In daily life, people walk and run on surfaces with different slopes (i.e., inclines and declines). However, it is still unknown whether flatfoot groups can keep the aforementioned advantages when walking on different slopes with arch support insoles, despite previous research evidence showed positive effects of the arch-support insole for the flatfoot [4, 16]. Hence, the purpose of this study was to investigate the effects of the arch-support insoles on stance time, cadence, peak pressure, and contact area of the foot with the ground while walking uphill, downhill, and on a level surface, respectively. We hypothesized that wearing arch-support insoles would decrease stance time, cadence, peak pressure, and contact area on each slope walking compared to wearing flat insoles.

Materials and methods

Participants

Since females tended to suffering from lower extremity injuries [2] and lack of flexible foot/shank coupling coordination compared to males [3], the current study only recruited 15 female college students diagnosed as flatfoot. The average age was 19.7 ± 4.3 years, the average height was 160.9 ± 6.0 cm, and the average weight was 56.5 ± 6.7 kg. Among them, the foot width was 7.7 ± 0.5 cm at the widest point and 5.0 ± 0.7 cm at the narrowest point, on average. A priori sample size calculation was performed using GPower (version 3.1.9.2, Franz Faul, University of Kiel, Kiel, Germany), with a power level of 80% and an α level of 0.05 [22]. The expected effect size was calculated using means (15.47 and 6.52) and standard deviation (6.87 and 4.7) of the midfoot contact area under soft and hard insole conditions [23]. It revealed that the sample size of 15 participants would be sufficient for the analysis. The static arch index for each participant was calculated as the foot width at the narrowest point divided by that at the widest point times 100% [8, 24]. This is also called the Chippaux and Smirakarc index (CSI) developed by Chippaux and Smirakarch [25]. The average arch indices was 64 ± 9%. Participants with arch indexes larger than 45% on both feet were considered to have flatfoot [24]. All participants were in good health and had no prior injuries or surgeries on their lower extremities.

All participants gave written informed consent prior to the experiment. The institutional review board of Antai Medical Care Corporation, Antai Tian-Sheng Memorial Hospital (TSMH, approval number 16-107-B1) reviewed and approved the study protocol.

Equipment

A wireless plantar-pressure insole system (Tekscan, Inc., Boston, MA, USA) was used to monitor the plantar pressure at a sampling rate of 100 Hz while each participant was walking. Wireless pressure insole with the F-Scan sensor (Model #3000E Tekscan, Inc., Boston, MA, USA) were placed above either the tested flat insole or arch-support insole of each foot to detect participant’s plantar pressure. The insole consists of 960 individual pressure measuring sensors, which are referred to as sensing elements.

Experimental protocols

The participants were instructed to walk on a treadmill with each of three slopes, a 9 degree incline (uphill walking), a -9 degree decline (downhill walking), and a level surface (level walking) [26, 27] at 0.75 m/s (2.7 km/h) speed for all slopes [26–28]. Uphill and downhill walking were performed on different days, since walking on uphill and downhill slopes should be performed on separate days with a lapse of 24 hours to avoid interference of concentric (uphill walking) and eccentric (downhill walking) contraction [29]. Level walking was assigned to be performed with either uphill or downhill walking on a same day. Participants performed a 3 min warm-up period on the treadmill at self-selected pace. Then, they walked on the adjusted treadmill for 30 seconds at one slope. There was a 6 min resting period between uphill/downhill and level walking trials.

All participants were asked to wear the same type of shoe (Arthur Ashe Int Low Python All Over, le coq sportif, France) with either a flat insole or arch-support insole (FOOTDISC, Global Action Inc., Taipei, Taiwan). The hardness values of the forefoot, midfoot, and heel parts of the flat insole and arch-support insole were measured using a hardness tester (Teclock GS-709N Type A; Teclock Co., Tokyo, Japan). The hardness tester was hold with both hands and pressed perpendicular to the plane of the forefoot, midfoot, and heel parts of the insole for five times, respectively. The value on the tester was recorded immediately each time. The averages of the hardness of each part of the insole are shown in Table 1.

Table 1. Hardness of the insole.

	Flat insole	Arch-support insole
Forefoot (pointer)	34.2±0.8	20.6±1.1
Midfoot (pointer)	19±1.2	60.0±0.7
Heel (pointer)	34.8±0.8	20.6±1.5

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Data processing

Tekscan software (Tekscan Inc., Boston, MA., USA) was used to analyse the stance time, cadence, peak plantar pressure, and plantar contact area from the pressure data of trial. The stance time was evaluated as the elapsed time from when the foot contacted the ground to when it was lifted again. Cadence means the number of steps taken per minute. The peak pressure was calculated for the big toe (BT), metatarsals 1–5 (M1-M5), midfoot (MF), medial heel (MH) and lateral heel (LH). The contact areas of the forefoot (FF), MF, and heel (H) were calculated and normalized to the sum of the contact areas of the FF, MF, and H; all values are expressed as percentages of the whole contact area. The calculation for the contact area was referred to Cavanagh’s (1987) arch index formula that was usually used to determine a flatter foot in a static standing posture [30]. Nevertheless, the current study used the formula to determine the contact area changes of the distribution of the FF, MF, and H when the foot was supported by the arch-support insole in dynamic walking movement. The aforementioned parameters were analysed for both feet, and the values from the two feet were averaged [31] to avoid discrepancies caused by the difference between the dominant and non-dominant legs.

Statistical analysis

SPSS 18.0 for Windows (SPSS Science Inc., Chicago, IL, USA) was used for the statistical analyses. A two-way repeated measures ANOVA was performed to compare the parameters between trials with participants wearing flat versus arch-support insoles for each slope. Levene’s test was used to test the homogeneity of the variances. A Kolmogorov-Smirnov test was used to evaluate the normality of the data, a Wilcoxon test was used when the data were not normally distributed. The Bonferroni’s method was used in post-hoc tests where applicable. The significance level was set at α = 0.05. The effect size (ES) for the difference between each pair of groups was calculated for each variable as a measure of the practical relevance of the significance using Cohen’s d; ES values between 0.20 and 0.49 were considered small, those between 0.50 and 0.79 were considered moderate, and those 0.80 and above were considered large [32].

Results

Stance time, cadence and step frequency

Table 2 shows the comparison of stance time, cadence and step frequency between the arch support insole and flat insole in each slope. The interaction with marginal significance between insoles and slopes was found in the stance time (p = 0.050). Simple main effects of slopes showed that the stance time in the arch-support insole was significantly shorter than that in the flat insole (p = 0.002, ES = 0.48) on the level surface. Simple main effects of insoles showed that the stance time of the uphill and level surfaces was significantly longer than that of the downhill surface in the arch-support (p = 0.019, ES = 0.89; p = 0.001, ES = 1.33, respectively) and flat (p = 0.009, ES = 1.04; p<0.001, ES = 1.77, respectively) insole. There was no interaction between insoles and slopes in the cadence. The main effect of slopes showed that the cadence of the downhill surface was significantly shorter than the uphill and level surfaces (p = 0.007; p<0.001, respectively). There was no statistically significant difference found between the insoles (p = 0.169). In addition, the interaction with marginal significance between insoles and slopes was found in the step frequency (p = 0.044). Simple main effects of insoles showed that the step frequency of the uphill and level surfaces was significantly shorter than that of the downhill surface in the arch-support (p< 0.001, ES = 1.22; p< 0.001, ES = 2.05, respectively) and flat (p = 0.004, ES = 1.02; p< 0.001, ES = 1.75, respectively) insole. Simple main effects of slopes showed that the step frequency has no difference among uphill (p = 0.132, ES = 0.10), downhill (p = 0.346, ES = 0.10), and level (p = 0.053, ES = 0.28) surface.

Table 2. Comparison of stance time, cadence and step frequency.

		Flat insole			Arch-support insole
		Left foot	Right foot	Average	Left foot	Right foot	Average
Stance time ^† (ms)
	Uphill	748.0±92.1	734.7± 86.2	741.3±88.6 ^a	740.0± 99.7	720.7±112.0	730.3±104.6 ^a
	Downhill	659.3±79.1	646.0±87.6	652.7±81.9 ^a, ^b	656.0±67.6	645.3±79.7	650.7±72.4 ^a, ^b
	Level ^*	795.3±66.6	776.0±70.5	785.7±67.7 ^b	766.0±79.9	735.3±80.1	750.7±77.9 ^b
Cadence ^# (step/min)
	Uphill ^a	51.2±6.0	51.2±5.9	51.2±5.9	50.7±6.2	51.3±7.3	51.0±6.6
	Downhill ^a, ^b	57.3±7.1	57.1±6.9	57.2±7.0	57.0±5.9	57.0±5.8	57.0±5.8
	Level ^b	47.9±4.3	48.2±4.1	48.0±4.2	49.4±4.9	50.2±4.7	49.8±4.7
Step frequency ^† (step/min)
	Uphill	-----	-----	103.7±11.8 ^a	-----	-----	102.5±12.4 ^a
	Downhill	-----	-----	116.1±12.5 ^a, ^b	-----	-----	117.3±11.8 ^a, ^b
	Level	-----	-----	97.5±8.3 ^b	-----	-----	100.1±10.0 ^b

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^† interaction found between the insole and slope,

* significant difference found between the flat insole and arch-support insole,

^# significant difference found among the slopes,

^a significant difference found between the uphill and downhill,

^b significant difference found between the downhill and level, p < 0.05.

Peak pressure

Table 3 shows the comparison of peak pressure between the arch-support insole and flat insole in each part of the foot for each slope. The interaction between insoles and slopes was found in the BT (p = 0.030) and MH (p = 0.007).

Table 3. Comparison of peak pressure.

		Flat insole			Arch-support insole
		Left foot	Right foot	Average	Left foot	Right foot	Average
BT ^† (kpa)
	Uphill ^*	303.8±186.0	284.4±173.4	294.1±172.0 ^a	458.5±317.1	356.9±236.1	407.7±250.0 ^a
	Downhill	288.6±119.6	281.1±140.9	284.8±111.1 ^b	370.9±208.5	274.5±135.3	322.7±133.9 ^b
	Level ^*	198.9±109.0	143.5±82.7	171.2±74.7 ^a, ^b	237.6±97.7	215.2±150.2	226.4±80.7 ^a, ^b
M1 ^# (kpa)
	Uphill ^c	245.6±87.1	246.3±112.2	245.9±96.9	244.1±116.3	275.3±155.0	259.7±119.5
	Downhill	189.7±104.6	213.3±129.7	201.5±110.0	228.2±149.7	212.3±147.2	220.2±138.8
	Level ^c	208.3±96.3	202.9±72.3	205.6±77.1	193.3±93.2	238.9±111.1	216.1±93.1
M2 ^* (kpa)
	Uphill	313.9±221.4	294.1±192.9	304.0±196.3	326.3±239.6	294.9±188.5	310.6±212.2
	Downhill	245.6±168.6	256.8±206.6	251.2±182.0	304.1±206.3	276.6±207.2	290.4±196.4
	Level	354.1±216.9	310.5±187.2	332.3±196.5	382.9±276.7	351.6±239.1	367.3±250.5
M3 ^*, ^#(kpa)
	Uphill	284.0±132.9	302.2±189.1	293.1±154.5	320.8±156.4	298.2±171.6	309.5±156.3
	Downhill ^b	211.5±120.6	225.5±145.4	218.5±128.6	279.8±166.3	256.8±165.6	268.3±158.7
	Level ^b	349.6±164.9	350.7±211.4	350.2±176.9	368.0±208.7	399.1±224.1	383.6±211.4
M4 ^*, ^#(kpa)
	Uphill	192.0±86.1	205.9±110.6	199.0±85.1	217.4±115.8	197.2±84.0	207.3±89.7
	Downhill ^b	121.8±48.4	142.1±61.0	132.0±45.8	150.5±74.0	153.5±80.4	152.0±66.2
	Level ^b	223.9±88.7	228.7±100.6	226.3±75.6	236.5±97.6	275.1±141.0	255.8±98.0
M5 ^# (kpa)
	Uphill	133.5±83.6	164.3±77.1	148.9±73.4	149.8±86.7	144.4±55.6	147.1±65.2
	Downhill ^b	95.7±38.2	114.2±51.4	105.0±39.2	111.1±48.0	114.0±55.5	112.6±46.7
	Level ^b	153.9±44.8	154.8±63.7	154.3±49.9	152.4±60.3	173.5±83.3	162.9±48.3
MF (kpa)
	Uphill	140.6±91.5	140.2±49.8	140.4±56.5	148.2±98.2	122.9±46.2	135.6±64.2
	Downhill	96.1±30.6	113.8±48.1	105.0±34.4	120.1±38.4	120.8±53.6	120.4±40.2
	Level	119.9±56.4	123.3±47.8	121.6±36.7	108.3±27.4	122.4±49.4	115.3±31.8
MH ^† (kpa)
	Uphill ^*	165.2±67.3	169.5±61.5	167.3±60.2 ^c	147.8±74.5	140.9±62.3	144.3±64.4 ^c
	Downhill ^*	232.5±156.2	211.8±116.5	222.1±134.2	197.1±136.1	138.7±98.4	167.9±114.2
	Level ^*	206.5±80.4	179.4±52.2	193.0±63.0 ^c	165.7±90.0	161.7±71.2	163.7±72.6 ^c
LH ^*, ^# (kpa)
	Uphill ^c	131.5±63.6	146.1±102.0	138.8±71.7	111.7±61.8	112.2±52.4	112.0±49.1
	Downhill	202.3±130.2	161.5±80.7	181.9±103.1	164.5±111.4	152.7±96.9	158.6±99.0
	Level ^c	173.7±82.0	165.1±103.3	169.4±76.1	129.3±51.7	189.1±162.6	159.2±90.5

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^† interaction found between the insole and slope,

* significant difference found between the flat insole and arch-support insole,

^# significant difference found among the slopes,

^a significant difference found between the uphill and downhill,

^b significant difference found between the downhill and level,

^c significant difference found between the uphill and level, p < 0.05; BT = big toe, M1 = metatarsal 1, M2 = metatarsal 2, M3 = metatarsal 3, M4 = metatarsal 4, M5 = metatarsal 5, MF = midfoot, MH = medial heel, LH = lateral heel.

BT

Simple main effects of slopes showed that the peak pressure of the BT in the arch-support insole was significantly greater than that in the flat insole on the uphill (p = 0.002, ES = 0.53) and level surface (p = 0.019, ES = 0.71). Simple main effects of insoles showed that the peak pressure of the BT of the uphill and downhill surfaces was significantly greater than that of the level surface in the arch-support (p = 0.016, ES = 0.98; p = 0.033, ES = 0.87, respectively) and flat (p = 0.018, ES = 0.59; p = 0.007, ES = 1.20, respectively) insole.

MH

Simple main effects of slopes showed that the peak pressure of the MH in the arch-support insole was significantly smaller than that in the flat insole on the uphill (p = 0.003, ES = 0.37), downhill (p<0.001, ES = 0.44) and level surface (p = 0.024, ES = 0.43). Simple main effects of insoles showed that the peak pressure of the MH on the uphill surface was significantly smaller than that of the level surface in the flat insole (p = 0.037, ES = 0.42).

There was no interaction between insoles and slopes in the peak pressure of the M1, M2, M3, M4, M5, MF and LH. The main effect of insoles showed that the peak pressure of the M2 (p = 0.036), M3 (p = 0.013) and M4 (p = 0.013) in the arch-support insole was significantly greater than that in the flat insole, while the LH (p = 0.013) in the arch-support insole was significantly smaller than that in the flat insole. The main effect of slopes showed that the peak pressure of the M1 (p = 0.028) on the uphill surface was significantly greater than that of the level surface, while the peak pressure of the LH (p = 0.028) on the uphill surface was significantly smaller than that of the level surface. The main effect of slopes showed that the peak pressure of the M3 (p = 0.006), M4 (p = 0.001) and M5 (p = 0.005) on the level surface was significantly greater than that on the downhill surface.

Contact area

Table 4 shows the comparison of contact areas of the FF, MF and H. There was no interaction between insoles and slopes in the FF, MF and H. The main effect of insoles showed that the contact area of the MF (p = 0.001) in the arch-support insole was significantly greater than that in the flat insole, while the contact area of the FF (p = 0.001) in the arch-support insole was significantly smaller than that in the flat insole.

Table 4. Comparison of contact area.

		Flat Insole			Arch-support insole
		Left foot	Right foot	Average	Left foot	Right foot	Average
FF ^* (%)
	Uphill	44.0±6.2	40.5±6.4	42.2±5.3	42.5±6.1	40.0±4.3	41.3±4.5
	Downhill	43.3±6.0	40.4±3.7	41.8±4.1	41.3±7.1	39.9±5.7	40.6±6.0
	Level	43.4±4.6	41.2±4.6	42.3±4.4	41.2±4.2	40.1±4.8	40.6±3.8
MF ^* (%)
	Uphill	28.6±7.7	30.1±6.3	29.4±6.2	30.8±6.6	31.0±5.1	30.9±5.2
	Downhill	31.0±4.5	27.4±9.6	29.2±6.1	32.1±4.1	28.0±10.3	30.0±5.4
	Level	30.2±6.4	27.7±7.4	29.0±6.1	32.1±5.1	29.0±7.9	30.5±4.8
H (%)
	Uphill	28.4±4.0	28.4±2.9	28.4±2.2	28.4±3.5	27.2±4.1	27.8±2.3
	Downhill	29.0±3.2	28.9±3.2	28.9±2.5	31.4±3.9	27.3±5.4	29.4±2.3
	Level	27.9±2.5	29.5±3.6	28.7±2.5	29.4±5.3	28.3±2.2	28.8±2.6

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* significant difference found between the flat insole and arch-support insole, p< 0.05; FF = forefoot, MF = midfoot, H = heel.

Discussion

The results of the current study showed that wearing the arch-support insole shortened the stance time compared with wearing the flat insole. Furthermore, the arch-support insole reduced the peak pressure on the medial heel when the foot contacted the surface during uphill, downhill and level walking. It also increased the peak pressure on the big toe, thus assisting the foot propulsion during uphill and level walking. Moreover, the arch-support insole also increased the peak pressures on metatarsals 2–4 to assist the propulsion during walking. The arch-support insole increased the contact area of the midfoot compared with the flat insole, providing support to the medial arch, which is important for people with flatfoot.

The result of the current study showed that the stance time had an interaction effect across insole and slope. However, the stance time of the arch-support being shorter than the flat insole only occurred in level walking, but not in uphill and downhill walking. The change in the stance time upon wearing the arch-support insole could reflect a change from a pathological gait to a normal one with respect to multiple characteristics [33]. Longer stance time reflects lower gait speed that is predictive of increased mortality in middle-aged and elderly people in level walking [34]. Previous studies indicated that mid-soles composed of harder materials provide better foot support and, thereby, shorten the stance time in level walking [35]. Moreover, greater insole hardness has been shown to not only improve the efficiency of each stance but also enhance the physiological sensation during level walking [36]. The midfoot of the arch-support insole used in the current study was harder than that of the flat insole and, as a result, the arch-support insole was associated with a significantly shorter stance time than the flat insole during level walking on a treadmill. It was suggested that the arch-support insole provided better support for the midfoot, which effectively shortened the stance time when walking on a level treadmill and may increase the gait speed when walking on the level ground [34].

Although the peak pressure of the MH demonstrated an interaction effect across insole and slope, it was significantly reduced in the arch-support insole during uphill, downhill and level walking compared to the flat insole. Walking requires periodic motion of the lower extremities, and many injuries to the lower extremities are related to the loading impact and over-pronation of the foot [13, 37]. Previous studies have shown that most of the physical stresses associated with walking are concentrated around the medial calcaneal tubercle [38]. Furthermore, the flatoot is closely associated with pain in the medial calcaneal tubercle [39, 40]. The function of the arch-support insole is thought to help restore the elasticity of the foot arch [41] for people with flatfoot, thereby reducing the foot pronation during uphill, downhill and level walking. The reduced medial heel peak pressure in the arch-support insole was speculated to reduce the heel striking impact and further facilitate the transfer of loading to improve stability and comfort [42] that would benefit people with flatfoot.

The peak pressure of the BT has an interaction effect across insole and slope in the current study. It was significantly greater in the arch-support insole than in the flat insole during uphill and level walking. Most people used the heel-strike strategy, in which the midfoot is responsible for transferring the plantar weight-bearing from the heel to the forefoot. The forefoot plays a crucial role in propulsion in the last phase of a stride [23, 43]. The BT of the forefoot in the arch-support insole was suggested to provide propulsion in uphill and level walking. Moreover, participants exhibited greater peak pressures on metatarsals 2–4 of the forefoot while wearing the arch-support insole than with the flat insole during level walking. This effect can be explained as an optimization of the heel lift by sharing a part of the heel load and assisting the foot propulsion during walking [43]. The arch-support insole may restore the function of medial foot arch, thereby facilitating the natural elastic stretch of the plantar fascia tension associated with the windlass mechanism [38, 44].

In the current study, the proportion of the contact area of the midfoot to that of the whole foot was greater with the arch-support insole than with the flat insole during uphill, downhill, and level walking. The finding is in agreement with a previous study showing that foot orthotics with a 30° inverted angle can increase the contact area of the medial midfoot [45]. Using the arch-support insole like using the foot orthotics inserted beneath the midfoot makes the contact area of the midfoot increased during walking. This increase in midfoot contact area in people with flatfoot may be associated with the support of the medial longitudinal foot-arch [46]. It was suggested that arch-support insoles can extend the contact area more evenly across in the forefoot, midfoot, and heel and, therefore, may better disperse the cumulative foot pressure over time to reduce the risk of soft-tissue injuries to the foot [47] during walking.

There were some limitations in the current study. The uphill, downhill, and level walking were performed on a treadmill in a laboratory, which did not realistically replicate the performance in an outdoor environment. Our finding did not apply to the male counterpart and people without the flatfoot problem. Only the static footprint index was used to evaluate the flatfoot in the current study, even though there are many methods, such as the navicular drop, rear foot eversion, foot posture index values, and many others, to determine the flatfoot population in the clinic [48]. The current study did not assess arch deformation in any way, thus discussion regarding the windlass mechanism were only speculations. In addition, the arch support insole did have higher hardness in the midsole and the flat insole was harder in the forefoot and the heel. This difference in stiffness could be a confounding variable to the results in the study and therefore, we cannot conclude that the differences were due to differences in hardness or the presence vs absence of an arch support.

Conclusions

These results imply that wearing an arch-support insole provides benefits in the shortened stance time. The arch-support insole helps absorb shock at the medial heel during uphill, downhill, and level walking, provided big toe propulsion during uphill and level walking, and applied metatarsals 2–4 propulsion during level walking compared with the flat insole. Furthermore, it facilitates more evenly distributed contact area over the entire foot. Based on these findings, we recommend that people with flatfoot wear arch-support insoles to restore the function of an elastic foot arch.

Supporting information

S1 Data

(ZIP)

Click here for additional data file.^{(240.7KB, zip)}

Data Availability

All relevant data are within the manuscript.

Funding Statement

The research leading to these results has received funding from the Ministry of Science and Technology of Taiwan (Grant No. MOST 106-2410-H-034-036), Doctoral Science and Research of Nantong University (Grant No. 135419619022) and Public Welfare Research Fund of Department of Science and Technology of Liaoning (Grant No. 20170027). No authors received a salary from any of the funders. All the funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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PLoS One. doi: 10.1371/journal.pone.0237382.r001

Decision Letter 0

Gianluca Vernillo

7 Apr 2020

PONE-D-20-05316

The arch support insoles show benefits to people with flatfoot on gait process time, plantar pressure and contact area

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Reviewer #1: General comments:

I would like to thank the editor for inviting me to review the manuscript entitled “The arch support insoles show benefits to people with flatfoot on gait process time, plantar pressure and contact area”. This study compared various plantar pressure measurements while walking on three slopes and while wearing two different types of insoles. Please find below my comments, which may aid the authors with submitting a revised version of their manuscript.

- I think that the authors made a great attempt to link their variables of interest to measures of importance to people with flatfeet. However, the authors attempted to link simple plantar pressure variables to mobility and walking benefits without describing what is meant by these terms. I would recommend to clearly state what is meant by the terms “mobility” and “benefits” and how improvements in mobility look like.

- One of the authors’ main conclusions, namely that increased midfoot area relative to total area in the arch-support insole is representative of the restoring of a “normal” arch is, in my opinion, an incorrect statement. If the loaded midfoot area increases, it means that more of the midfoot is in contact with the ground. This would mean that the foot is actually in a more flattened position. I would strongly recommend revising the statements made upon these findings.

- Lastly, I would recommend removing figure 1, as it does not provide valuable information to the understanding of the methods of this paper. I would also recommend providing all units within tables 1-4 instead of including them in the table headings. The units in table 1 are unclear. Also, the p-values and Cohen’s d effect sizes should be provided for all comparisons in all tables.

Specific comments:

Line 43: In the introduction of the main text, you have not mentioned any previous study investigating increased pressure at the hip, knee, or ankle joints in people with flat feet; but you talk about it in the background section of the abstract. Please either introduce the observed changes at the hip, knee, and ankle joints from the previous studies in the introduction of the main text or delete this statement from the background section of the abstract. Also, I would strongly recommend to change the wording from “pressure on the lower back, hip, …” to “loading on the lower back, hip, …”.

Line 44: “… and risk serious damage to these joints …”. You have not provided any evidence for this statement in the main text. Please either remove this statement from the abstract or elaborate on this and provide references in the main text.

Line 51: Please consider rephrasing the sentence to “The significance level α was set to 0.05.”

Lines 52-58: Please include Cohen’s d effect sizes for the reported comparisons. Also, please reorder the results section so that you always mention the same insole first in your comparisons. This would make it easier for the reader to follow your findings.

Line 60: It is unclear how your reported findings “provide benefits in mobility”. You cannot make this statement with the results that you presented in the above section unless you clearly demonstrate how these variables are related to benefits in mobility.

Line 74: “… suffers from rigid the flatfoot …”: remove “the” from the sentence

Line 80: Please include a reference at the end of the sentence.

Lines 83-84: This sentence suggests that flatfoot can result in damage to internal organs and the brain. This is incorrect. Please remove this statement from the manuscript.

Line 87: Please include a reference at the end of the sentence.

Line 91: I think using the term “cure rate” is inappropriate for two reasons: 1) leg internal rotation and leg length discrepancy is not a “disease” and therefore cannot be “cured”, 2) wearing insoles does not “cure” anything, it may reduce excessive leg internal rotation or offset leg length discrepancy. Please replace the term “cure rate” with a more appropriate term.

Line 95: the peak vertical ground reaction force is not the propulsion force. They are probably related to each other but they are not the same. Therefore, please remove “(i.e., propulsion)” from the sentence.

Lines 102-104: this sentence is the same as the sentence before that. Please remove this sentence and include its references to the previous sentence.

Lines 106-108: this is not a hypothesis. Clearly state how wearing the arch-insole will affect your variables of interest.

Line 112: remove “with” from the sentence.

Line 116: Consider rephrasing the sentence to: “A priori sample size calculation was performed using GPower (Company, City, Country), …”.

Line 118: Why were the means and standard deviations for the medial-lateral COP used to perform the sample size calculations if these are not the variables of interest in your study?

Line 122: the plural of “index” is “indices”

Line 123: “… were considered to have the flatfoot …”. Remove “the” from the sentence.

Lines 125-127: the review board that approved this study is not affiliated with any institution of any of the authors. Could you please elaborate on that?

Line 134-135: Please consider rephrasing the sentence to: “The insole consists of 960 individual pressure measuring sensors.”

Lines 142-143: Please consider rephrasing the sentence to: “Each subject performed a 3 min warm-up period on the treadmill at self-selected pace.”

Lines 143-147: In one sentence you say that participants walked on all slopes one after the other with a 6 min break in between slopes. In the next sentence, however, you state that walking on different slopes was performed on different days. Those are contradicting statements. Which one is true?

Line 151: How was the hardness measured exactly. More information is needed.

Line 158: “gait process time”. This variable is typically referred to as “stance time” or “ground contact time”. Please consider changing this throughout the manuscript to not confuse the reader.

Line 161: remove “each” from the sentence.

Line 177: Please include a reference for how Cohen’s d effect sizes were calculated.

Line 185: was there a difference in stance times for the other slopes? Even if not, please include a sentence stating so and also include the p-value and effect size for the comparison.

Lines 190-212: Please change the order of reporting your comparisons. Sometimes you first mention the arch-support insole and other times you first mention the flat insole. Please pick one insole that you will always mention first in your comparisons. This would confuse the reader less.

Lines 210-211: please include your p-values and ES right after the slope condition.

Lines 217-219: you said that the arch-support insole shortened the time of each gait cycle. This is incorrect. A gait cycle goes from the heel strike of one foot to the heel strike of the same foot. Your findings showed, however, that the stance times were altered. Please revise.

Line 218: you state that mobility was improved. None of your variables of interest is a measure for mobility. At least you did not make good enough of a case that a variable you investigated actually represents mobility. Please provide more evidence that stance times are a legitimate measure for mobility or remove this statement from the paper.

Line 220: you state that the arch-support insole absorbed the shock associated with the foot contacting the ground. Again, this is a pure speculation and you have not provided any evidence that this is the case. Please provide the evidence or delete this statement from the manuscript.

Lines 238-239: I do not understand this sentence. Please elaborate what you want to say here.

Lines 244-245: It is only a speculation that wearing arch-support insoles will “restore a normal, elastic arch in people with flatfoot, …”. Please clearly state that this is only a speculation or include a reference that has shown this in the past. Also, what is a “normal” arch?

Lines 247-249: You cannot make this statement. You have not demonstrated why reducing peak pressures would be a benefit for people with flatfoot. Please make a better case of how you link peak pressure to substantial benefits in people or remove this statement.

Lines 256-258: How does wearing an arch-support insole restore a “normal”, elastic arch? What do you speculate is the mechanism behind it? Again, what is “normal”? Perhaps, you should not use this term.

Lines 258-265: You have not assessed arch deformation in any way in this study; yet, you discuss the windlass mechanism and how the arch may or may not collapse with these insoles. I would strongly recommend highlighting that these are speculations, only, or remove the entire paragraph from the manuscript.

Lines 269: how would the forefoot play a crucial role in the braking during downhill walking if all participants were striking with the heel? The forefoot will mainly still be in the air during the braking period of the stance phase. Therefore, the forefoot cannot contribute to the braking at all. Again, this is a speculation because you have not assessed forefoot motion. Please remove this statement from the paper.

Lines 276-278: If the area of the midfoot increases relative to the total area, then the foot is flatter compared to when the midfoot area is lower compared to the total area. This is also called the arch index (Cavanagh, 1987). Your conclusion, therefore, does not make sense. Please revise.

Line 281: remove “make” from the sentence.

Lines 293-294: you cannot make the statement that wearing the arch-support insole provided many benefits in mobility. You have not provided clear reasoning as to why this would be the case. Please remove this statement from the paper.

Reviewer #2: The purpose of this study was to determine if persons with flatfoot (i.e., per planus) changed the pressure distribution across the foot while walking uphill, downhill, or on even ground in flat or arch supported insoles. The study indicated that the “gait process time”, the pressure distribution, and contact area were different in the flat or arch support insoles, but seemed to be dependent on the walking condition. I believe there needs to be some improvements in the analysis and interpretation before this manuscript is ready for publication.

I have a number of minor comments, but those may become irrelevant after the major comments are addressed. Here are my major comments.

1. The statistics need to change. There was a comparison of insole condition across different levels of incline. The results seemed to indicate that the variables that were different across insole conditions seemed to be dependent on the level of incline. With this observation in mind, the researchers should re-run the statistics on each dependent variable and instead of conducting multiple uncorrected t-tests, they should conduct a two way repeated measures ANOVA with factors INCLINE (uphill, level, downhill) and INSOLE (flat, arch support). This will indicate if there is an interaction effect for the measured pressure and gait variables.

2. Why did you restrict you sample to only females, particularly when the condition seems to be more common in males? Please provide an explanation why there wasn’t any males.

3. Please provide an explanation as to why your static arch index was representative of flatfoot. My understanding is that flat foot would have something to do with the proportion of the foot that is or is not in contact with the ground in a loaded or unloaded condition. What does the narrowest and widest part of the foot have to do with the arch collapsing or per planus?

4. Where was the pressure insole placed relative to the insoles (i.e., underneath or above)? Please provide an explanation why you used on placement method over the other.

5. How much of the results were due to hardness/stiffness of the insole versus it having arch support or not? For example, there was a difference in midsole hardness in the arch support condition and this condition also presented with an increase contact area. The same results applies to the forefoot area such that the harder condition showed increase contact area.

6. Please change “gait process time” to stance time that would be more consistent with the literature.

7. Please present the data across the dominant and non-dominant leg. If in one leg there was higher peak pressure and lower peak pressure in the other, this would average out to no change in pressure. I don’t think your averaging method avoids discrepancies.

Please incorporate these changes and adjust the discussion accordingly. Once those comments are addressed, I will be able to provide more feedback on the minor, or major, comments that remain.

**********

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Reviewer #1: Yes: Sasa Cigoja

Reviewer #2: No

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PLoS One. 2020 Aug 20;15(8):e0237382. doi: 10.1371/journal.pone.0237382.r002

Author response to Decision Letter 0

27 May 2020

RESPOND to Reviewer #1:

General comments:

RESPOND:

Thank you for your comment. We have changed the term “mobility” to gait speed. Studenski, et al. (2011) indicated that longer stance time reflects lower gait speed that is predictive of increased mortality in middle-aged and elderly people. The shortened stance time found in the current study was speculated to increase the gait speed because of wearing the arch-support insole. In addition, we have removed this statement from conclusion that “wearing the arch-support insole provided many benefits in mobility”. Please refer to lines 242-247. These results imply that wearing an arch-support insole provides benefits in the shortened stance time and generation of propulsion force to the big toe while walking on uphill and level surfaces and to the metatarsals 2-4while walking on the level surface. We have stated these in abstract and conclusion section. Please refer to lines 61-63 and 306-310.

Reference:

Studenski S, Perera S, Patel K, Rosano C, Faulkner K, Inzitari M, et al. Gait speed and survival in older adults. Jama. 2011; 305(1): 50-58. doi:10.1001/jama.2010.1923

RESPOND:

Thank you for your comment. We have revised all the statements and removed the word “normal” throughout the manuscript.

RESPOND:

Thank you for your comment. We have removed figure 1. We provide all units within tables 1-4. We changed the statistical method to a repeat-measures two-way ANOVA according to another reviewer’s comment. There would be many p-values and Cohen’s d effect sizes. It was hard to present them in tables. So they were provided in the text of the manuscript. Please refer to tables 1-4 and results section.

Specific comments:

RESPOND:

Thank you for your comment. We have revised the abstract and mentioned that the flatfoot would increase the risk of foot injury and even lead to thumb valgus, tendinitis, plantar fasciitis, metatarsal pain, knee pain, lower-back pain conducted from previous studies. Please refer to lines 43-44.

RESPOND:

Thank you for your comment. We have removed this statement from the abstract and mentioned that the flatfoot would increase the risk of foot injury and even lead to thumb valgus, tendinitis, plantar fasciitis, metatarsal pain, knee pain, lower-back pain conducted from previous studies. We also elaborated on this and provide references in the main text. Please refer to lines 43-44 and 81-84.

Line 51: Please consider rephrasing the sentence to “The significance level α was set to 0.05.”

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 50-51.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 54-59.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 61-63.

Line 74: “… suffers from rigid the flatfoot …”: remove “the” from the sentence

RESPOND:

Thank you for your comment. We have removed “the” from the sentence. Please refer to line 74.

Line 80: Please include a reference at the end of the sentence.

RESPOND:

Thank you for your comment. We include a reference at the end of the sentence. Please refer to line 80.

Lines 83-84: This sentence suggests that flatfoot can result in damage to internal organs and the brain. This is incorrect. Please remove this statement from the manuscript.

RESPOND:

Thank you for your comment. We have removed this statement from the manuscript. Please refer to lines 82-84.

Line 87: Please include a reference at the end of the sentence.

RESPOND:

Thank you for your comment. We have revised the sentence and include a reference at the end of the sentence. Please refer to line 88.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to line 92.

RESPOND:

Thank you for your comment. We have removed “(i.e., propulsion)” from the sentence. Please refer to lines 94-96.

Lines 102-104: this sentence is the same as the sentence before that. Please remove this sentence and include its references to the previous sentence.

RESPOND:

Thank you for your comment. We have removed this sentence and include its references to the previous sentence. Please refer to lines 98, 100-101.

Lines 106-108: this is not a hypothesis. Clearly state how wearing the arch-insole will affect your variables of interest.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 106-108.

Line 112: remove “with” from the sentence.

RESPOND:

Thank you for your comment. We have removed “with” from the sentence. Please refer to lines 112.

Line 116: Consider rephrasing the sentence to: “A priori sample size calculation was performed using GPower (Company, City, Country), …”.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to line 116.

Line 118: Why were the means and standard deviations for the medial-lateral COP used to perform the sample size calculations if these are not the variables of interest in your study?

RESPOND:

Thank you for your comment. We have changed the variable to “contact area” to perform the sample size calculations. Please refer to lines 117-119.

Line 122: the plural of “index” is “indices”

RESPOND:

Thank you for your comment. We have revised the word. Please refer to lines 123.

Line 123: “… were considered to have the flatfoot …”. Remove “the” from the sentence.

RESPOND:

Thank you for your comment. We have removed the word. Please refer to lines 123-124.

Lines 125-127: the review board that approved this study is not affiliated with any institution of any of the authors. Could you please elaborate on that?

RESPOND:

The experiment was practiced in Chinese Culture University. And all participants were recruited from Chinese Culture University. Chinese Culture University does not have its own review board. Chinese Culture University usually cooperates with Antai Tian-Sheng Memorial Hospital. That’s why the review board approved this study is not affiliated with any institution of any of the authors.

Line 134-135: Please consider rephrasing the sentence to: “The insole consists of 960 individual pressure measuring sensors.”

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 135-136.

Lines 142-143: Please consider rephrasing the sentence to: “Each subject performed a 3 min warm-up period on the treadmill at self-selected pace.”

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 145-146.

RESPOND:

Thank you for your comment. Uphill and downhill walking were performed on different days, since walking on uphill and downhill slopes should be performed on separate days with a lapse of 24 hours to avoid interference of concentric (uphill walking) and eccentric (downhill walking) contraction [27]. Level walking was assigned to be performed with either uphill or downhill walking on a same day. Participants performed a 3 min warm-up period on the treadmill at self-selected pace. Then, they walked on the adjusted treadmill for 30 seconds at one slope. There was a 6 min resting period between uphill/downhill and level walking trials. We have revised the sentences. Please refer to lines 141-145.

Line 151: How was the hardness measured exactly. More information is needed.

RESPOND:

Thank you for your comment. We have increase more information. Please refer to lines 151-156.

RESPOND:

Thank you for your comment. We have revised this throughout the manuscript. Please refer to lines 48, 54, 67, 107, 161, 163, 189, 190, 192, 193, 194, 250, 252, 254 and 258.

Line 161: remove “each” from the sentence.

RESPOND:

Thank you for your comment. We have removed “each” from the sentence. Please refer to lines 161-162.

Line 177: Please include a reference for how Cohen’s d effect sizes were calculated.

RESPOND:

Thank you for your comment. We include a reference in the sentence. Please refer to line 170.

Line 185: was there a difference in stance times for the other slopes? Even if not, please include a sentence stating so and also include the p-value and effect size for the comparison.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 199-200 and table 2.

RESPOND:

Thank you for your comment. We have revised these sentences and always keep the arch-support insole be first mentioned. Please refer to lines 205-237.

Lines 210-211: please include your p-values and ES right after the slope condition.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 208-218.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 242-243.

RESPOND:

Thank you for your comment. We have removed the word “mobility” and revised the sentence. Please refer to lines 243-245 and table 2.

RESPOND:

Thank you for your comment. We delete this statement from the manuscript. Please refer to line 246.

Lines 238-239: I do not understand this sentence. Please elaborate what you want to say here.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 262-263.

RESPOND:

Thank you for your comment. We have revised the sentence and included a reference. Please refer to lines 267-269.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 269-272.

RESPOND:

Thank you for your comment. We have revised the sentence. Please refer to lines 281-283.

RESPOND:

Thank you for your comment. We have removed the entire paragraph from the manuscript. Please refer to lines 284-286.

RESPOND:

Thank you for your comment. We have removed this statement from the paper. Please refer to line 290.

RESPOND:

Thank you for your comment. In the current study, the contact area of the midfoot was measured with pressure insoles with sensors that were placed between the tested insole and foot during walking. The method of the measurement of the contact area for dynamic walking movement is kind of different from that of Cavanagh’s (1987) arch index for a static standing posture that usually uses a scanner with bare foot on it. The measurement of Cavanagh’s (1987) arch index is usually used to determine a flatter foot in a static standing posture. Nevertheless, the current study used Cavanagh’s formula to determine changes of the distribution of the parts of the foot when it was supported by the arch-support insole in walking movement. Using the arch-support insole like using foot arch-support orthotics inserted beneath the midfoot makes the contact area of the midfoot increased during walking. We have elaborated this statement in the method and this paragraph. Please refer to lines 288-293 and 168-172.

Line 281: remove “make” from the sentence.

RESPOND:

Thank you for your comment. We have removed “make” from the sentence. Please refer to line 291.

RESPOND:

Thank you for your comment. We removed this statement from the paper. Please refer to lines 306-30.

RESPOND to Reviewer #2:

1.The statistics need to change. There was a comparison of insole condition across different levels of incline. The results seemed to indicate that the variables that were different across insole conditions seemed to be dependent on the level of incline. With this observation in mind, the researchers should re-run the statistics on each dependent variable and instead of conducting multiple uncorrected t-tests, they should conduct a two way repeated measures ANOVA with factors INCLINE (uphill, level, downhill) and INSOLE (flat, arch support). This will indicate if there is an interaction effect for the measured pressure and gait variables.

RESPOND:

Thank you for your comment. We considered the reviewer’s comment to conduct a two-way repeated measures ANOVA with factors. The purpose of this study was mainly to compare the differences between the arch-support insole and flat insole in each of three slopes, respectively. Therefore, some of significance of the slopes did not discussed in the manuscript. Please refer to lines 178, 189-240 of the methods section, results and tables 2-4.

2. Why did you restrict you sample to only females, particularly when the condition seems to be more common in males? Please provide an explanation why there wasn’t any males.

RESPOND:

Thank you for your comment. We currently only recruit females this time in case of some homogeneity issues. We will further recruit male participants and compare the difference between males and females.

RESPOND:

Thank you for your comment. There are around 30 methods to evaluate the flatfoot (Banwell et. al, 2018; Cavanagh & Rodgers, 1987). There are two conditions of measuring the static arch index. One is in a body-weight loaded condition; another is in an body-weight unloaded condition. The current study used the measurement in a body-weight loaded condition. The static arch index is related to the ratio between the smallest width of the midfoot and the largest width of the metatarsal head area (Gill, Lewis, and DeSilva, 2014). This is also called the Chippaux and Smirakarc index (CSI) developed by Chippaux and Smirakarch. The CSI is correlated with skeletal measures of arch height such as the navicular height. People with flatfoot tend to have lower arch height during a stance based on a footprint. Then, the narrowest part of the foot will increase and change the CSI. The CSI had reliability and validity to measure and define flat foot populations (Gill, Lewis, and DeSilva, 2014).

Reference:

Banwell HA, Paris ME, Mackintosh S, Williams CM. Paediatric flexible flat foot: how are we measuring it and are we getting it right? A systematic review. Journal of Foot & Ankle Research. 2018; 11(1): 21-33. doi:10.1186/s13047-018-0264-3

Cavanagh PR, Rodgers MM. The arch index: a useful measure from footprints. Journal of Biomechanics. 1987; 20(5): 547–51. doi: 10.1016/0021-9290(87)90255-7

Gill SV, Lewis CL, DeSilva JM. Arch Height Mediation of Obesity-Related Walking in Adults: Contributors to Physical Activity Limitations. Physiology Journal. 2014; Article ID 821482 doi: 10.1155/2014/821482

4. Where was the pressure insole placed relative to the insoles (i.e., underneath or above)? Please provide an explanation why you used on placement method over the other.

RESPOND:

Thank you for your comment. Wireless pressure insole with the F-Scan sensor (Model #3000E Tekscan, Inc., Boston, MA, USA) were placed above either the tested flat insole or arch-support insole of each foot to detect participant’s plantar pressure. The pressure insole was placed between the tested insole and foot to measure the contact pressure variables of the foot on the tested insole. If the pressure insole is placed underneath the tested insole, the contact pressure variables would be the tested insole rather than the foot and they may be affected by many other factors such as the thickness and the shape of the insole itself.

RESPOND:

Thank you for your comment. The arch-support insole provide support in the midsole with greater hardness compared with the flat insole. However, the current study cannot show how much of the results were due to hardness of the insole versus it having arch support or not. It has been claimed in the limitation. Please refer to lines 301-303.

6. Please change “gait process time” to stance time that would be more consistent with the literature.

RESPOND:

Thanks for the comment. We have revised this throughout the manuscript. Please refer to lines 48, 54, 67, 107, 161, 163, 189, 190, 192, 193, 194, 250, 252, 254 and 258.

Please incorporate these changes and adjust the discussion accordingly. Once those comments are addressed, I will be able to provide more feedback on the minor, or major, comments that remain.

RESPOND:

Thanks for the comment. We provided the data of dominant and non-dominant leg. Please refer to table 2-4. In addition, foot pressure was collected by F-Scan sensor (Model #3000E Tekscan, Inc., Boston, MA, USA) in the stance phase for each foot. In a stance phase, the F-Scan sensor counted the support foot pressure, while the swing foot pressure did not be counted. We averaged data of dominant and non-dominant leg measured during stance phases.

Attachment

Submitted filename: Response to Reviewers #2 ped 200526.docx

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PLoS One. doi: 10.1371/journal.pone.0237382.r003

Decision Letter 1

Gianluca Vernillo

3 Jun 2020

PONE-D-20-05316R1

The arch support insoles show benefits to people with flatfoot on stance time, plantar pressure and contact area

PLOS ONE

Dear Dr. Chen-Yi Song,

Please submit your revised manuscript by Jul 18 2020 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Gianluca Vernillo, Ph.D.

Academic Editor

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #2: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Reviewer #1: I have only one question left to the authors addressing my first comment of the first round of revisions:

I think that the authors made a great attempt to link their variables of interest to measures of importance to people with flatfeet. However, the authors attempted to link simple plantar pressure variables to mobility and walking benefits without describing what is meant by these terms. I would recommend to clearly state what is meant by the terms "mobility" and "benefits" and how improvements in mobility look like.

Authors' response:

Thank you for your comment. We have changed the term "mobility" to gait speed. Studenski, et al. (2011) indicated that longer stance time reflects lower gait speed that is predictive of increased mortality in middle-aged and elderly people. The shortened stance time found in the current study was speculated to increase the gait speed because of wearing the arch-support insole. In addition, we have removed this statement from conclusion that "wearing the arch-support insole provided many benefits in mobility". Please refer to lines 242-247. These results imply that wearing an arch-support insole provides benefits in the shortened stance time and generation of propulsion force to the big toe while walking on uphill and level surfaces and to the metatarsals 2-4while walking on the level surface. We have stated these in abstract and conclusion section. Please refer to lines 61-63 and 306-310.

Reference:

Studenski S, Perera S, Patel K, Rosano C, Faulkner K, Inzitari M, et al. Gait speed and survival in older adults. Jama. 2011; 305(1): 50-58. doi:10.1001/jama.2010.1923

New question:

How can gait speed be increased if your participants were walking at a set speed on a treadmill? According to your methods in line 141, your participants were walking at 0.75 m/s. I would hope that their gait speed did not change between conditions. The stance times may have changed but this would infer a change in step frequency or swing time as well. Was this the case?

Reviewer #2: Thank you to the authors for making some of the requested changed. The authors will still need to address the following comments:

1. Please provide the rationale as to why only females were recruited in the text of the manuscript under the methods section.

2. You did not provide a sufficient statement of the hardness of the insoles as a limitation. You need to be specific. You should be stating that the arch support insole did have higher hardness in the midsole and the flat insole was harder in the forefoot and the heel. This difference in stiffness could be a confounding variable to the results in the study and therefore, you cannot conclude that the differences were due to differences in hardness or the presence vs absence of an arch support

3. Your purpose statement reads “the purpose of this study was to investigate the effects of the arch-support insoles on stance time, cadence, peak pressure, and contact area of the foot with the ground while walking uphill, downhill, and on a level surface, respectively.” In the discussion, you did not provide much explanation of the interaction effects that were found. You need to perform a post-hoc analysis on the interaction effects to determine the location of the interaction effect. For example, stance time had an interaction effect across insole and slope. It appears that this difference occurred in level walking, but not uphill and downhill walking. This needs to be determined with the post-hoc analysis and then an interpretation should be provided in the discussion. Please complete this type of analysis and interpretation for each interaction effect.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Sasa Cigoja

Reviewer #2: No

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2020 Aug 20;15(8):e0237382. doi: 10.1371/journal.pone.0237382.r004

Author response to Decision Letter 1

7 Jul 2020

Reviewer #1: I have only one question left to the authors addressing my first comment of the first round of revisions:

Response:

Thank you for your comment. We have removed the term "mobility" throughout the discussion. We focused to mention the benefits to the people with flatfeet from wearing the arch-support insole in the shortened stance time when walking on a level treadmill found in the current study. It was speculated to increase the gait speed when walking on the level ground. Studenski, et al. (2011) indicated that longer stance time reflects lower gait speed that is predictive of increased mortality in middle-aged and elderly people. We have stated these in the abstract and conclusion sections. Please refer to lines 71-73, 277-279 and 337-340.

Reference:

1. Studenski S, Perera S, Patel K, Rosano C, Faulkner K, Inzitari M, et al. Gait speed and survival in older adults. Jama. 2011; 305(1): 50-58. doi:10.1001/jama.2010.1923

New question:

RESPOND:

Thank you for your comment. We agreed with the review’s comment that the gait speed would not change when walking at a set speed on a treadmill. We have rephrased the sentence and further investigated changes in step frequency. We found that there was an interaction between the insole and slope in the step frequency. In addition, the interaction with marginal significance between insoles and slopes was found in the step frequency (p=0.044). Simple main effects of insoles showed that the step frequency of the uphill and level surfaces was significantly shorter than that of the downhill surface in the arch-support (p< 0.001, ES=1.22; p< 0.001, ES=2.05, respectively) and flat (p=0.004, ES=1.02; p< 0.001, ES=1.75, respectively) insole. Simple main effects of slopes showed that the step frequency has no difference between the insoles on the uphill (p=0.132, ES=0.10), downhill (p=0.346, ES=0.10), and level (p=0.053, ES=0.28) surface. Please refer to lines 214-221 and Table 2.

Reviewer #2: Thank you to the authors for making some of the requested changed. The authors will still need to address the following comments:

1. Please provide the rationale as to why only females were recruited in the text of the manuscript under the methods section.

RESPOND:

Thank you for your comment. Previous study has estimated the prevalence of mild and severe cases of the flatfoot to be 16.2% among males and 11.7% among females which was close to each other in gender (Tenenbaum et al., 2013). Nevertheless, females are more likely to suffer from risks of lower extremity injuries in running (Alomonroeder & Benson, 2017) and lack of flexible foot/shank coupling coordination compared to males (Noghondar & Yazdi, 2017). We have provided the rational in the introduction. Please refer to lines 83-86 .

References:

(1) Tenenbaum S, Hershkovich O, Gordon B, Bruck N, Thein R, Derazne E, et al. Flexible pes planus in adolescents: body mass index, body height, and gender--an epidemiological study. Foot & Ankle International. 2013; 34(6): 811-817. doi: 10.1177/1071100712472327

(2) Alomonroeder TG, Benson LC. Sex differences in lower extremity kinematics and patellofemoral kinetics during running. J Sport Sci. 2017; 35(16): 1575-1581. doi: 10.1080/02640414.2016.1225972

(3) Noghondar FA, Yazdi NK. Assessment of patterns and variability in lower extremity coordination between genders with different shoe insole stiffness during jump-landing tasks. Human Movement. 2017; 18(1): 37–43. doi: 10.1515/humo-2017-0002

RESPOND:

Thank you for your comment. We have added the review’s comment regarding the hardness of the insoles in the limitation section. Please refer to lines 330-334.

RESPOND:

Thank you for your comment. We have performed a post-hoc analysis on the interaction effects and provided information regarding the interaction effects in the discussion section. Please refer to lines 273-275, 289-291, 301-303, and 305-307.

Attachment

Submitted filename: RESPOND to Reviewer #2 ped 200707.docx

Click here for additional data file.^{(18.5KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0237382.r005

Decision Letter 2

Gianluca Vernillo

16 Jul 2020

PONE-D-20-05316R2

The arch support insoles show benefits to people with flatfoot on stance time, plantar pressure and contact area

PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

Reviewer #1: All comments have been addressed

Reviewer #2: (No Response)

**********

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Reviewer #1: Yes

Reviewer #2: Yes

**********

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Reviewer #2: Yes

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Reviewer #1: Thank you for addressing my comments. I would recommend that the paper is accepted for publication once the set of data that is needed to reproduce the findings and conclusions of this study are made publicly available (e.g., online data repository) as per PLOS Data policy.

Reviewer #2: You have addressed two of my comments thoroughly and one partially. For comment 1 with respect to recruiting only females, you need to state this reason explicitly in the methods section after you mention that only females were recruited. In its current form, this selection criteria is unclear. Please insert a comment at the beginning of the methods section that addresses this choice.

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PLoS One. 2020 Aug 20;15(8):e0237382. doi: 10.1371/journal.pone.0237382.r006

Author response to Decision Letter 2

22 Jul 2020

Response:

Thank you for your comment. We uploaded the data to the online data repository as per PLOS Data policy.

Response:

Thank you for your comment. We have inserted a comment at the beginning of the methods section that addresses this choice. Please refer to lines 124-126.

PLoS One. doi: 10.1371/journal.pone.0237382.r007

Decision Letter 3

Gianluca Vernillo

27 Jul 2020

The arch support insoles show benefits to people with flatfoot on stance time, plantar pressure and contact area

PONE-D-20-05316R3

Dear Dr. Song,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Reviewer #2: All comments have been addressed

**********

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Reviewer #2: Yes

**********

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Reviewer #2: Yes

**********

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Reviewer #2: Yes

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Reviewer #2: Yes

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PLoS One. doi: 10.1371/journal.pone.0237382.r008

Acceptance letter

Gianluca Vernillo

3 Aug 2020

PONE-D-20-05316R3

The arch support insoles show benefits to people with flatfoot on stance time, plantar pressure and contact area

Dear Dr. Song:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

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Thank you for submitting your work to PLOS ONE and supporting open access.

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on behalf of

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Associated Data

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Data Availability Statement

All relevant data are within the manuscript.

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PERMALINK

The arch support insoles show benefits to people with flatfoot on stance time, cadence, plantar pressure and contact area

Yu-ping Huang

Hsien-Te Peng

Xin Wang

Zong-Rong Chen

Chen-Yi Song

Roles

Abstract

Background

Methods

Results

Conclusions

Introduction

Materials and methods

Participants

Equipment

Experimental protocols

Table 1. Hardness of the insole.

Data processing

Statistical analysis

Results

Stance time, cadence and step frequency

Table 2. Comparison of stance time, cadence and step frequency.

Peak pressure

Table 3. Comparison of peak pressure.

BT

MH

Contact area

Table 4. Comparison of contact area.

Discussion

Conclusions

Supporting information

Data Availability

Funding Statement

References

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Gianluca Vernillo

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Author response to Decision Letter 0

Decision Letter 1

Gianluca Vernillo

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Author response to Decision Letter 1

Decision Letter 2

Gianluca Vernillo

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Author response to Decision Letter 2

Decision Letter 3

Gianluca Vernillo

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Acceptance letter

Gianluca Vernillo

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Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

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