Abstract
he purpose of this study was to compare the mechanical properties of a non- cushioned minimalistic shoe and cushioned shoe during walking at 6 and running at 10 and 14 km·h −1 in habituated female runners. Twelve habituated female runners completed two trials (cushioned shoe vs. minimalist shoe) with three within-trial speeds (6, 10, and 14 km·h −1 ) in a counter-balanced design. Flexible pressure insole sensors were used to determine kinetic variables (peak vertical impact force, average loading rate, active vertical peak force, time to active peak vertical force, and impulse) and spatiotemporal variables (stride duration, cadence, ground contact time, swing time, and time to midstance). Cush- ioned running shoes exhibited greater energy absorption (690%), recovered energy (920%), and heat dissipation (350%). The cushioned shoes significantly reduced peak vertical impact (~12%) and average loading rate (~11%) at running speeds 10–14 km·h −1 . However, these effects were not observed during walking, nor did the cushioned shoes influence peak active force, impulse, stride duration, ground contact or swing time. Cushioned running shoes provide significant benefits in energy absorption, energy recovery, and
dissipation (350%). The cushioned shoes significantly reduced peak vertical impact (~12%) and average loading rate (~11%) at running speeds 10–14 km·h −1 . However, these effects were not observed during walking, nor did the cushioned shoes influence peak active force, impulse, stride duration, ground contact or swing time. Cushioned running shoes provide significant benefits in energy absorption, energy recovery, and heat dissipation, which decrease impact-related forces and loading rates in female runners without changing the spatiotemporal variables of gait. Keywords:gait; running; females; injury; ground reaction forces 1. Introduction On a global scale, walking [1] and running [2] are some of the most popular physical activities undertaken by the general population. The collision between foot and ground during fast walking or running generates a shockwave of energy on every step, necessitating passive attenuation processes to protect vital systems [3–6]. Both activities face challenges as these passive processes are highly sensitive to factors such as impact force magnitude, loading rate, and repetition [7,8]. All of these are exacerbated at faster paces, particularly at speeds >12 km·h −1 , which involve increases in stride length and/or stride frequency [9–14]. To reduce these forces, midsole cushioning serves as an important feature of footwear in providing a foam layer between the outsole and innersole. Its functional definition revolves around the ability to reduce vertical ground reaction force upon impact [15,16] and to enhance energy absorption during loading [17]. Holistically, the properties focus Appl. Sci.2025,15, 1120 https://doi.org/10.3390/app15031120
Appl. Sci.2025,15, 1120 2 of 12 on absorbed, lost, and recovered energy. To this end,in vitromechanical tests show that midsoles are effective at absorbing impact energy [18]. However, the findings in the literature regarding the effectiveness of such cushioning capabilities while running are somewhat inconclusive [11,19–22]. Moreover, few research articles report the actual cushioning properties of the shoes being tested, as per industry standards [23–26], making it hard to establish a cause. Early studies indicated that midsole softness did not reduce peak impact [11,27]. How- ever, it was later found that runners adapt their technique (joint kinematics) to compensate for changes in surface-impact-absorbing characteristics [28] and shoe cushioning [26]. Shoes with greater cushioning tend to result in a narrower range of motion at the ankle in the transverse plane, less internal rotation at the hip, and reduced knee abduction [29]. Con- sequently, it is believed that runners operate within a personal kinetic bandwidth when responding to impact stresses [30]; they adapt their technique to cope with impact stresses, suggesting that footwear plays a significant role. Importantly, running or walking barefoot, or with minimal cushioning, alters gait through decreasing stride length and increasing stride frequency, which, in turn, reduces ground reaction forces and their associated metrics [31,32]. Thus, it is hypothesized that the change in stride kinematics, rather than the absence of shoes, leads to the reduction in impact forces [33]. Moreover, the effects of wearing minimalistic shoes whilst running have provided mixed results. Some studies have shown significantly lower impact forces compared to maximally cushioned shoes [34], while others have found no difference or even increased loading rate or peak impact forces compared to cushioned shoes worn when running and/or walking [21,35–38]. The proposition that cushioning does not attenuate impact is not tenable [18] and can be related to force plates reflecting whole-body acceleration rather than lower extremity to predict ground reaction forces [18]. However, the use of pressure insoles alignin vivowith in vitro, where comparisons between minimalist and traditional running shoes in female- only populations have shown considerably greater peak pressure and maximum mean pressures for the forefoot, midfoot,
is not tenable [18] and can be related to force plates reflecting whole-body acceleration rather than lower extremity to predict ground reaction forces [18]. However, the use of pressure insoles alignin vivowith in vitro, where comparisons between minimalist and traditional running shoes in female- only populations have shown considerably greater peak pressure and maximum mean pressures for the forefoot, midfoot, and rearfoot in minimalist shoes [19]. Further, maximally cushioned shoes decrease in-shoe plantar loading forces from a total perspective and at the forefoot when compared with minimalist shoes [39]. However, there is currently no link between plantar pressures and impact forces in minimalist and maximally cushioned shoes. It is no surprise that researchers are calling for more biomechanical studies involv- ing gait kinetics in relation to shoe cushioning [18] and based on gender [40], as female runners are at an increased risk of running-related injuries compared to their male coun- terparts[7,41,42] , have slightly different patterns of gait [40], and present greater shock attenuation than males [43]. This could mean either lower tolerance to peak impact forces or they are experiencing greater forces on impact and may respond differently to different shoe conditions based on gait and anatomy [19,39,44,45]. The popularity of running, combined with the potential negative health effects, par- ticularly for female runners, due to the shockwave generated upon ground contact with every step, underscores the necessity of exploring shoe material properties to mitigate these risks. Whilein vitrotests show that midsole cushioning is beneficial, these results do not consistently translate to real-world running, where equivocal findings are attributed to factors such as changes in kinematics, running speed, challenges related to habituation to multiple conditions, and protocol design. This study aims to address these issues by comparing the mechanical properties of a non-cushioned minimalistic shoe with those of a cushioned shoe. Using the same footwear, it will also assess the spatiotemporal and kinetic variables of gait via pressure-
Appl. Sci.2025,15, 1120 3 of 12 sensitive insoles whilst walking at 6 km·h −1 and running at 10 and 14 km·h −1 in a group of habituated female runners. 2. Materials and Methods 2.1. Participants Twelve recreational to nationally competitive female endurance runners (mean±SD; age (yrs.) 24.2±6.2, height (cm) 167.0±4.4, body mass (kg) 62.3±6.6, and Body Mass Index 22.3±2.1) free of injury participated, after giving written consent in accordance with University Human Ethics Committee approval. All participants grew up in New Zealand where barefoot activity is socially normal [46], and all still participate actively barefoot, to some extent. They were also accustomed to running on asphalt using modern (circa 2023) cushioned shoes. This sample size was based on an a priori power analysis using G*power (Ver- sion 3.1.9.7, Heinrich-Heine University, Dusseldorf, Germany) and the findings of Shorten et al. [18] . The effect size for peak impact force between a minimalist shoe and a less cushioned shoe than used for this study, running at 14.4 km·h −1 , was 0.51. For the analysis of variance (ANOVA) with repeated measures within factors, there was an alpha value of 0.05, power of 0.95, and effect size of 0.51. The output suggested 8 participants, providing an actual power of 0.964. A further power analysis using peak pressure on impact [39], where participants were free to run at a self-selected speed using minimalist and maximal cushioned shoes, pre- sented an effect size of 0.7 with an output sample size of 5 (actual power 0.97). Considering these findings, we aimed for the inclusion of twelve participants. 2.2. Procedures and Measurements The experimental protocol consisted of two trials (cushioned shoe vs. minimalist- control shoe) and three condition walk–run treadmill speeds (6, 10, and 14 km·h −1 ) that were typically used by the participants in their everyday running shoe. These speeds have also been shown to produce significant differences in vertical ground reaction forces [12]. Each trial was performed in one session on the same day, performed in a counter- balanced order of shoe conditions, and separated by 15 min to minimise the sequence effect on
) that were typically used by the participants in their everyday running shoe. These speeds have also been shown to produce significant differences in vertical ground reaction forces [12]. Each trial was performed in one session on the same day, performed in a counter- balanced order of shoe conditions, and separated by 15 min to minimise the sequence effect on the dependent variables of interest. Upon arrival at the laboratory, the participants were measured, weighed, and had their footwear size determined for each foot (Figure) by a shoe specialist to ensure best fit based on participant input and expertise. The mean (range) in a United States women’s size was 8.5 (7.5–9.5) for the cushioned shoe and 8 (6–10) for the non-cushioned shoe.Appl. Sci. 2025, 15, x FOR PEER REVIEW 3 of 12 footwear, it will also assess the spatiotemporal and kinetic variables of gait via pressure- sensitive insoles whilst walking at 6 km·h −1 and running at 10 and 14 km·h −1 in a group of habituated female runners. 2. Materials and Methods 2.1. Participants Twelve recreational to nationally competitive female endurance runners (mean ± SD; age (yrs.) 24.2 ± 6.2, height (cm) 167.0 ± 4.4, body mass (kg) 62.3 ± 6.6, and Body Mass Index 22.3 ± 2.1) free of injury participated, after giving written consent in accordance with Uni- versity Human Ethics Committee approval. All participants grew up in New Zealand where barefoot activity is socially normal [46], and all still participate actively barefoot, to some extent. They were also accustomed to running on asphalt using modern (circa 2023) cushioned shoes. This sample size was based on an a priori power analysis using G*power (Version 3.1.9.7, Heinrich-Heine University, Dusseldorf, Germany) and the findings of Shorten et al. [18]. The effect size for peak impact force between a minimalist shoe and a less cush- ioned shoe than used for this study, running at 14.4 km∙h −1 , was 0.51. For the analysis of variance (ANOVA) with repeated measures within factors, there was an alpha value of 0.05, power of 0.95, and effect size of 0.51. The output suggested 8
The effect size for peak impact force between a minimalist shoe and a less cush- ioned shoe than used for this study, running at 14.4 km∙h −1 , was 0.51. For the analysis of variance (ANOVA) with repeated measures within factors, there was an alpha value of 0.05, power of 0.95, and effect size of 0.51. The output suggested 8 participants, providing an actual power of 0.964. A further power analysis using peak pressure on impact [39], where participants were free to run at a self-selected speed using minimalist and maximal cushioned shoes, presented an effect size of 0.7 with an output sample size of 5 (actual power 0.97). Consid- ering these findings, we aimed for the inclusion of twelve participants. 2.2. Procedures and Measurements The experimental protocol consisted of two trials (cushioned shoe vs. minimalist- control shoe) and three condition walk–run treadmill speeds (6, 10, and 14 km·h −1 ) that were typically used by the participants in their everyday running shoe. These speeds have also been shown to produce significant differences in vertical ground reaction forces [12]. Each trial was performed in one session on the same day, performed in a counter- balanced order of shoe conditions, and separated by 15 min to minimise the sequence effect on the dependent variables of interest. Upon arrival at the laboratory, the participants were measured, weighed, and had their footwear size determined for each foot (Figure 1) by a shoe specialist to ensure best fit based on participant input and expertise. The mean (range) in a United States women’s size was 8.5 (7.5–9.5) for the cushioned shoe and 8 (6–10) for the non-cushioned shoe. Figure 1. Photographic representation of (A) the minimalist shoe and (B) the cushioned shoe. Figure 1B shows the cushioned shoe (Asics Gel-Nimbus 25, Asics Corporation, Kobe, Japan), which had a 40.5 mm heel and a 32.5 mm forefoot (8 mm drop) midsole featuring Figure 1.Photographic representation of (A) the minimalist shoe and (B) the cushioned shoe. FigureB shows the cushioned shoe (Asics Gel-Nimbus 25, Asics Corporation, Kobe, Japan), which had a 40.5 mm heel and a 32.5
the cushioned shoe (Asics Gel-Nimbus 25, Asics Corporation, Kobe, Japan), which had a 40.5 mm heel and a 32.5 mm forefoot (8 mm drop) midsole featuring Figure 1.Photographic representation of (A) the minimalist shoe and (B) the cushioned shoe. FigureB shows the cushioned shoe (Asics Gel-Nimbus 25, Asics Corporation, Kobe, Japan), which had a 40.5 mm heel and a 32.5 mm forefoot (8 mm drop) midsole fea- turing a single layer of FlyteFoam BLAST TM ECO Plus foam cushioning with an extra PureGEL TM insert in the rearfoot, and had a rocker (manually measured using Kinovea,
Appl. Sci.2025,15, 1120 4 of 12 version 0.9.5 [47]) angle of 15 ◦ , rocker radius of 45 ◦ , apex position of 70%, apex angle of 75 ◦ , and a weight of 235±9 g. The midsole hardness scale C, measured with a durometer (HC), was 30.1±0.1 HC. FigureA shows the minimalist shoe [ 48], which had a 0 mm heel–toe drop, a 5 mm PVC rubber outsole (H&S, The Warehouse, Auckland, New Zealand), and weighed 206±14 g, with a midsole durometer reading of 55.0±6.1 HC. Trial order was selected, and the appropriate footwear was fitted with a flexible pressure insole to record kinetic data (LoadSol ® Pro, Novel GmbH, Munich, Germany), whereupon each insole (left and right) was configured for the specific participant and followed the manufacturer’s bipedal calibration process. Each trial consisted of a 5 min warm-up period on the treadmill (Life Fitness, Hamilton, New Zealand) at the participant’s preferred running speed. Each condition (shoe*speed) was performed for a period of 1 min, with data logged throughout and analysed during the last 10 s of each condition [49]. The participants were blind to any dependent variables being measured. LoadSol ® time*force data (200 Hz) were uploaded into MATLAB (R2022b, MathWorks, Inc., Natick, MA, USA), re-sampled to 1000 Hz, and processed using force threshold values of 20–30 N to determine the initial foot contact and toe-off [50]. From these outputs, the following dependent variables were calculated using techniques previously described for walking [51] and running [52] and expressed per body weight (N) where appropriate: (a) Peak vertical impact force (N·BW −1 ), identified as the first peak between initial contact and the active peak. If the first peak was not present in running (mid-forefoot strike), it was defined as the force at 13% of the stance phase; (b) Active peak vertical force (N·BW −1 ), which was the second peak for walkers and heel strike runners, or the highest force reading of each step for mid-forefoot strikers. In running, this point (mid-stance) was described where the foot was directly below the centre of mass. In walking, the midstance
as the force at 13% of the stance phase; (b) Active peak vertical force (N·BW −1 ), which was the second peak for walkers and heel strike runners, or the highest force reading of each step for mid-forefoot strikers. In running, this point (mid-stance) was described where the foot was directly below the centre of mass. In walking, the midstance occurs at the lowest vertical force reading between the two peaks; (c) Time to mid-stance (s), which was the time to the lowest force value between peak 1 and 2 in walking, and the time to the active peak force in running; (d) To calculate the average rate of loading (N·BW −1 · s −1 ), the difference between forces at 20% and 80% of the peak impact force was divided by the corresponding time interval (s) between these two points; (e) Impulse (N·s), the area under the force–time curve; (f) Ground contact time (s), the time the foot remained in contact with the floor; (g) Swing time (s), the time the foot had no contact with the ground; and (h) Stride duration, which was the time from one initial impact to the next initial impact for the same foot. Mechanical Testing A shoe cushioning property assessment was performed post running trials using a modified industry standard test (ISO 20344:2021 (5.17)) [53]. The Instron (4467, Instron, Norwood, MA, USA) was programmed to compress the midsole in the vertical direction at a deformation rate of 10 mm per minute and applied a maximum force of 2.2 kN. Following 20 conditioning cycles, 5 cycles were performed while recording deformation (mm) and load (N). Energy absorption (J) was calculated as the area under the load–extension curve until peak extension was met. Recovered energy (J) was calculated as the area under the load–extension curve from the peak extension to the return to zero extension. The recovered energy (%) is calculated as (recovered energy/energy absorbed) *100, while heat dissipation (J) is the difference between the energy absorbed and the recovered energy. All dependent variable data were calculated per step, with the number of steps, overall
(J) was calculated as the area under the load–extension curve from the peak extension to the return to zero extension. The recovered energy (%) is calculated as (recovered energy/energy absorbed) *100, while heat dissipation (J) is the difference between the energy absorbed and the recovered energy. All dependent variable data were calculated per step, with the number of steps, overall mean±SD, and the mean±SD of the coefficient of variation (CV (%)) per independent variable presented. Differences between shoes and speed were analysed using a two-way repeated-measures ANOVA, with 2 within-subject variables (speed*shoe). Where signifi-
Appl. Sci.2025,15, 1120 5 of 12 cant difference was found, Sidak’s post hoc multiple comparisons testing was performed. All statistics were performed using GraphPad Prism (V 8.4, GraphPad Software, San Diego, CA, USA). Significance was set atp< 0.05. 3. Results 3.1. Mechanical Properties The mechanical testing resulted in a deformation of 3.39 mm, and 22.37 mm for the fifth cycle in the minimalist-control and cushioned shoe, respectively. The deformation curves and relevant data for the two shoes are presented in Figure.Appl. Sci. 2025, 15, x FOR PEER REVIEW 5 of 12 variable presented. Differences between shoes and speed were analysed using a two-way repeated-measures ANOVA, with 2 within-subject variables (speed*shoe). Where signifi- cant difference was found, Sidak’s post hoc multiple comparisons testing was performed. All statistics were performed using GraphPad Prism (V 8.4, GraphPad Software, San Di- ego, CA, USA). Significance was set at p < 0.05. 3. Results 3.1. Mechanical Properties The mechanical testing resulted in a deformation of 3.39 mm, and 22.37 mm for the fifth cycle in the minimalist-control and cushioned shoe, respectively. The deformation curves and relevant data for the two shoes are presented in Figure 2. Figure 2. Force deformation curves and corresponding values of energy absorption, energy return, heat dissipation, and elastic return (%) for the minimalist-control shoe (−) and the cushioned shoe (--). 3.2. Kinetic Data Analysis A two-way ANOVA of kinetic data identified significant interaction (speed*shoe) for peak vertical impact (F (2,22) = 11.44, p = 0.005, Figure 3A), with a main effect for speed (F (2,22) = 22.93, p < 0.0001) but not shoes (F (1,11) = 0.916, p = 0.361). Key post hoc multiple comparison between shoes indicated decreased impact differences for cushioned shoes versus mini- malistic control at both 10 km·h −1 (1.42 vs. 1.32 N·BW −1 , p = 0.009) and 14 km·h −1 (1.72 vs. 1.51 N·BW −1 , p = 0.005). There was also a significant interaction (speed*shoes) for average loading rate (F (2,22) = 5.456, p = 0.013, Figure 3C), with main effects for both speed (F (2,22) = Figure 2.Force deformation curves and corresponding
Description
This study compares shoe cushioning effects on gait parameters in female runners.