Influence of rearfoot and forefoot midsole hardness on ...

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Influence of rearfoot and forefoot midsole hardness on biomechanical and perception variables during heeltoe running a

Thorsten Sterzing , Vreni Schweiger Brauner a

a b

a

a

, Rui Ding , Jason Tak-Man Cheung & Torsten

b

Li Ning Sports Science Research Center, Beijing, China

b

Faculty of Sports & Health Science, Conservative & Rehabilitative Orthopedics, Technische Universität, München, Germany Version of record first published: 04 Mar 2013.

To cite this article: Thorsten Sterzing , Vreni Schweiger , Rui Ding , Jason Tak-Man Cheung & Torsten Brauner (2013): Influence of rearfoot and forefoot midsole hardness on biomechanical and perception variables during heel-toe running, Footwear Science, DOI:10.1080/19424280.2012.757810 To link to this article: http://dx.doi.org/10.1080/19424280.2012.757810

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Footwear Science, 2013 http://dx.doi.org/10.1080/19424280.2012.757810

Influence of rearfoot and forefoot midsole hardness on biomechanical and perception variables during heel-toe running Thorsten Sterzinga*, Vreni Schweigera,b, Rui Dinga, Jason Tak-Man Cheunga and Torsten Braunerb a

Li Ning Sports Science Research Center, Beijing, China; bFaculty of Sports & Health Science, Conservative & Rehabilitative Orthopedics, Technische Universit€ at M€ unchen, Germany

Downloaded by [Dr Thorsten Sterzing] at 16:40 04 March 2013

(Received 16 August 2012; final version received 9 December 2012) Purpose: Running shoe cushioning research has focused widely on rearfoot (RF) characteristics, whereas forefoot (FF) characteristics have been rather neglected. However, altered cushioning may affect running biomechanics and respective subjective perception at RF and FF. Thus, this research compared the effect of running shoes with different midsole hardnesses at RF and FF. Methods: Twenty-eight heel-toe runners were tested in five experimental shoe conditions that featured three segmented EVA midsoles (RF, midfoot (MF), FF). Three conditions had the same midsole hardness at RF and FF (soft (SS), medium (MM), hard (HH)). Two conditions had different RF and FF midsole hardness (soft-RF/hard-FF (SH), hard-RF/soft-FF (HS)). All midsoles featured the same MF segment of medium hardness. Vertical ground reaction forces and lower extremity kinematics during stance, subjective cushioning of the heel-toe transition and the overall comfort were quantified. Data were analysed using Kolmogorov-Smirnov tests, repeated measures ANOVA, Bonferroni post-hoc tests (p < 0.05), and effect size analyses (ph2). Results: The consistent midsole shoe conditions showed increased maximum loading rates of impact and propulsion peaks from SS to HH. Respective maximum loading rates of SH were similarly to SS, and respective maximum loading rates for HS were similar to HH. Subjectively, the consistent midsole conditions were rated according to their mechanical properties and softer shoes were preferred over harder shoes. In the varied midsole shoe conditions, SH was perceived similar to SS, whereas HS was perceived similar to MM. Conclusion: The examined biomechanical variables were influenced almost entirely by respective RF cushioning properties. The hard FF did not negatively affect cushioning perception as long as the RF was soft. Combining a soft FF with a hard RF improved inferior cushioning perception associated with shoes being hard at RF and FF. Keywords: footwear; cushioning; pronation; biomechanics; perception

1. Introduction When running, the human body is exposed to repetitive impacts resulting from sudden decelerations at initial ground contact. These accumulated impacts are considered a risk factor for the development of overuse running injuries (James et al., 1978; Clarke et al., 1983; Milner et al., 2006). Consequently, injury prevention by reducing these is claimed to be a major function of running shoe cushioning. However, further research suggests that high impact forces and high loading rates during running are not necessarily linked to injuries (Nigg, 2001). Instead, improvement of footwear comfort and regulation of soft tissue vibration are stated as additional purposes of running shoe cushioning by some authors (Nigg & Wakeling, 2001; Nigg et al., 2003; Nigg, 2010). Thus, running shoe cushioning is associated with multiple functions and consequently it resembles a strong demand of runners. In a recent running shoe questionnaire, cushioning was rated among the most important properties of running shoes *Corresponding author. Email: [email protected] Ó 2013 Taylor & Francis

(24.8%), besides fit (49.6%) and comfort (15.8%) (Schubert et al., 2011). Running shoe cushioning can be modified by their mechanical midsole properties and may be additionally quantified by biomechanical and subjective testing procedures (Clarke et al., 1983; Milani et al., 1997; Hennig, 2011). Strong relationships between biomechanical and subjective cushioning variables were observed in running shoes that varied in their midsole material hardness at the heel and midfoot (Milani et al., 1997). Often, the loading rate of the first impact peak of the vertical ground reaction force curve is used in biomechanical analyses for kinetic quantification of cushioning characteristics during heel-toe running. This variable has been shown to consistently correlate with rearfoot hardness of running shoes (Clarke et al., 1983; De Wit et al., 1995; Heidenfelder et al., 2008). The loading rate was also able to characterize rearfoot cushioning differences of running shoes featuring different crash-pad heights (Heidenfelder


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et al., 2010). Kinematic analyses demonstrated that runners adapt their running style in response to shoe and surface hardness (Tenbroek et al., 2011). For barefoot running some researchers showed that runners changed their strike pattern from rearfoot to midfoot or forefoot (De Wit et al., 2000; Divert et al., 2005; Lieberman et al., 2010; Hamill et al., 2011). However, also in a comparison of shod running it has been shown that differences in mechanical heel hardness of running shoes may lead to heel strike adaptation of runners. When rearfoot hardness of running shoes is increased runners reduce their sagittal shoe-ground contact angle (Heidenfelder et al., 2008). Regarding sex and age subgroup kinematics of the lower extremity, it has been shown that the influence of different midsole hardness of running shoes was subject-independent (Nigg et al., 2012). Subjectively, runners were shown to perceive differences in running shoe hardness according to its mechanical properties. Thereby, soft shoes were preferred over hard ones and shoes having harder forefoot characteristics were perceived as particularly uncomfortable (M€ undermann et al., 2002). However, assessment of preferred cushioning characteristics are strongly dependent on the range of material stiffness of test shoes used and results may not be seen as absolute but rather study specific. The FF has been widely neglected in the analysis of running shoe cushioning. The majority of biomechanical running shoe cushioning studies has focused on RF characteristics. This is probably due to the majority of athletes running heel-toe (Hasegawa et al., 2007), only switching to midfoot and forefoot strike patterns at higher velocities (Keller et al., 1996). Furthermore, it is noteworthy that research examining the subjective assessment of running shoe cushioning, in most cases, does not distinguish between RF and FF characteristics. Therefore, the purpose of this research was to examine the influence of mechanically different RF and FF midsole hardness on cushioning, stability and foot-roll by usage of biomechanical and subjective variables. It was hypothesized that biomechanical variables are dependent on RF hardness alone, whereas subjective variables are dependent on both RF and FF hardness.

2. Methods Twenty-eight male, heel-toe runners (23.8 2.0 years, 1.77 0.04 m, 70.2 7.4 kg), being injury free at the time of testing, participated in this study. Average running experience of participants was 6.7 2.4 years and weekly running distance was 22.6 7.8 km. Participants had Brannock foot size 9.0 0.5 (The Brannock Device Co., Liverpool, NY, USA). All of them provided written informed consent prior to participation in this research. Five experimental running shoes (US men size 9.0) with identical, flexible mesh uppers and identical outsoles were used in this study. Their midsoles were preselected and featured three separate sections (RF, MF, FF) with distinct mechanical hardness characteristics (Figure 1, Table 1). All midsoles featured similar hardness of 501 Asker C at the MF segment. FF and RF sections differed in hardness within the range of common running shoe cushioning properties. Three shoe conditions had consistent hardness at RF and FF (soft-RF/soft-FF (SS), mediumRF/medium-FF (MM), hard-RF/hard-FF (HH)). Two shoe conditions had varied midsole hardness at RF and FF (softRF/hard-FF (SH), hard-RF/soft-FF (HS)). Participants were not told about the specific nature of the experimental shoe conditions, which all had the same visual appearance. Mechanical midsole characterization The EVA foam midsoles of the experimental shoes were pre-selected based on mechanical hardness. They had a total length of 291 mm, RF thickness of 26 mm and FF thickness of 16 mm for all shoe conditions. Midsole mass differed slightly due to respective material density. A Dial Durometer, 1600 Asker C, SP-698 (Rex Durometers, Rex Gauge Co., Buffalo Grove, IL, USA) was used to determine material hardness. Midsole hardness was measured at five locations (ASTM D 2240) on the EVA skin of RF, MF, and FF (Figure 1). Mechanical impact characteristics of the RF were measured with an impact tester (Exeter Research V2.6, Brentwood, NH, USA) by taking the average of the last 5 impacts from a total of 30 repetitive impacts. Drop height was 50 mm and drop mass was 8.5 kg. MF was not impact tested due to its uneven shape and FF

Table 1. Mean ( SD) of right midsole mechanical characteristics, left midsoles in similar range. RF Impact

RF Hardness

MF Hardness

FF Hardness

Shoe

Weight [g]

Peak Acceleration [g]

Time to Peak Acceleration [ms]

Energy Return [%]

Durometer Points [Asker C]



SH SS MM HH HS

309 299 312 327 312

9.85 ± 0.09 10.19 ± 0.05 11.51 ± 0.06 13.80 ± 0.04 13.98 ± 0.05

15.8 ± 0.1 14.1 ± 0.1 11.7 ± 0.0 9.4 ± 0.2 9.5 ± 0.2

53.1 ± 0.7 51.3 ± 0.6 44.1 ± 0.4 48.2 ± 0.2 49.1 ± 0.3

43.8 ± 1.1 47.1 ± 0.2 54.2 ± 1.1 62.0 ± 0.7 62.8 ± 0.8

49.0 ± 0.7 50.2 ± 0.8 52.2 ± 0.5 49.4 ± 1.4 51.0 ± 0.7

60.0 ± 1.0 48.0 ± 0.8 52.4 ± 0.9 61.7 ± 0.4 45.6 ± 1.1


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Figure 1. Midsole dimensions and impact measurement location at RF (left); hardness measurement locations on RF, MF, and FF (right).

was not impact tested due to its small thickness causing mechanical bottoming out when tested without other shoe components. Mechanical testing of the midsoles was performed under controlled environmental conditions (temperature: 23.0 1.3 C, humidity: 47.2 3.1%RH). Biomechanics Laboratory measurements were carried out on a 13m runway. Running speed was set to 3.3 0.1 m/s and controlled by timing gates (Brower Timing Systems, Salt Lake City, UT, USA) located 120 cm in front and behind a force plate (1000 Hz, 9060 cm, AMTI, Watertown, MA, USA). Participants performed five valid trials per shoe condition by striking the force plate with their right foot. Experimental shoe conditions were tested in randomized order. Prior to actual data collection, subjects warmed up individually, wearing their own shoes. They

were then familiarized to the procedure and testing equipment. Lower extremity kinematics were collected using a six-camera motion capture system (200 Hz, Vicon, Metrics Ltd, Oxford, UK). Reflective markers were placed at anatomical landmarks of the pelvis and the right leg. Four segments were defined: Pelvis, thigh, shank, and foot. Calibration markers were affixed on the right and left posterior superior iliac spine and anterior superior iliac spine, the great trochanter, lateral and medial knee epicondyles, lateral and medial malleoli, and metatarsal heads I and V (shoe markers). A five-marker tracking cluster was attached at the lateral side of the thigh and a four-marker tracking cluster at the lateral side of the lower leg. Additional tracking markers (shoe markers) were attached at the distal and proximal posterior heel and to the lateral rearfoot (Heiderscheidt et al., 2002). Kinetic analysis of vertical ground reaction force included ground contact time, peak vertical force I,

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maximum loading rate I, peak vertical force II, and maximum loading rate II. Kinematic variables were sagittal shoe-surface angle at initial ground contact and maximum plantar flexion velocity, rearfoot range of motion, rearfoot pronation velocity, knee flexion angle at initial ground contact and maximum knee flexion angle during stance.


Perception For subjective assessment participants ran two times 300 m in each shoe condition on a 100 m outdoor running loop at individual preferred speeds. Running speed was kept constant between shoe conditions, which were randomized among participants. Assessed variables were perceived cushioning intensity and cushioning preference (NSRL, 2003) during the first 300 m, which were marked on visual analogue scales right thereafter. Then, heel to toe transition and overall comfort were assessed during running the second 300 m and were also marked right thereafter. Requested ratings referred to the whole ground contact and were not separated for RF and FF in order to avoid conscious attention to the specific nature of the experimental shoe conditions. The visual analogue scales were anchored as follows: cushioning intensity: very hard (0 cm) to very soft (15 cm), cushioning preference: dislike extremely (0 cm) to like extremely (15 cm), heel-toe transition: very unsmooth (0 cm) to very smooth (15 cm), overall comfort: very uncomfortable (0 cm) to very comfortable (15 cm). Data processing and statistics A fourth-order Butterworth lowpass filter was applied to kinetic data at 150 Hz and to kinematic data at 30 Hz. Kinematic data were processed using Visual 3D software (C-Motion, Rockville, MD, USA). Biomechanical parameters of the repetitive trials for each shoe and subject were averaged. Biomechanical and perception statistics were analysed using Microsoft Excel and IBM SPSS (20, IBM Corp., Armonk, NY, USA). Shoe means and standard deviations were calculated across subjects. All data were normally distributed according to Kolmogorov-Smirnov tests. One-way repeated measures ANOVA and Bonferroni corrected post-hoc tests were performed accordingly. All alpha level were set to p < 0.05 a priori. For evaluation of effect sizes of shoe differences, partial eta square estimates (ph2) were calculated.

3. Results In all experimental conditions all participants showed a functional heel-toe foot strike pattern that is characterized by substantial load bearing at the heel during the phase of initial contact. Thus, vertical ground reaction force curves contained two peaks, a lower first impact peak referring to

heel strike and a higher second peak characterising further foot unroll and forefoot push-off (Figures 2 and 3). Biomechanics Kinetic variables of this study are displayed in Table 2. Ground contact time did not differ between experimental conditions. Shoe differences were observed for loading rate max I (p < 0.001) and loading rate max II (p < 0.001) (Figure 4). The shoe conditions featuring soft or medium RF hardness (SH, SS, MM) showed significantly reduced loading rates max I compared to shoe conditions featuring a hard RF hardness (HH, HS). Loading rate max II values were approximately one third of loading rate max I values in all shoe conditions. For loading rate max II, SH showed significantly reduced values compared to MM, HH, and HS. SS showed significantly reduced values compared to HH and HS. MM showed a significant reduction compared to HH. Although not significant, HS showed a decrease in loading rate max II compared to HH (p ¼ 0.313). Among all other kinetic variables, only one shoe comparison (SH to HH) indicated a significant difference regarding peak vertical force I, however, effect size for this variable was low (ph2 ¼ 0.112). Kinematic analysis exhibited shoe differences for various variables (Table 3). Maximum plantar flexion velocity was lower for shoe conditions featuring softer RF hardness (p < 0.001). Sagittal shoe surface angle was slightly lower for MM compared to SH and HS, however effect size was low (ph2 ¼ 0.199). Pronation velocity was reduced in shoe conditions featuring softer RF hardness (p < 0.001). However, rearfoot range of motion was lower only for SS compared to three other shoe conditions (p < 0.001). Maximum knee flexion angle was not affected by shoe conditions over stance and only SS compared to MM displayed a significant reduction of knee flexion angle at initial ground contact. Perception All perception variables revealed differences between shoe conditions (Table 4, Figure 5). Cushioning intensity for shoe conditions with consistent midsole hardness at the RF and FF were perceived significantly different (p < 0.001) and according to their mechanical material characteristics (SS softer than MM, MM softer than HH). SH was perceived similarly to SS. HS was perceived softer than HH and similar to MM. Cushioning preference ratings (p < 0.001) were closely related to cushioning intensity ratings (p < 0.001), revealing that the group of subjects preferred the softer shoe conditions over the harder ones. Heel-toe transition was perceived to be less smooth for HH compared to SH and SS. Overall comfort was rated significantly lower for HH compared to all other shoe conditions (p < 0.001). No significant overall comfort differences were observed between the other shoe conditions.

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Figure 2. Mean vertical ground reaction force curves with stance normalized to 101 data points.

Figure 3. Mean vertical ground reaction force curves with stance normalized to 101 data points (exploded view of first peak characteristics).

out that the examined biomechanical and perception variables were influenced mainly by RF cushioning properties. A minor influence of FF cushioning properties was observed for certain shoe conditions and variables.

4. Discussion This study examined the influence of running shoe cushioning on biomechanical and perception variables. RF and FF cushioning characteristics of running shoes were modified by variation of midsole hardness. It turned Table 2. Kinetic variables (mean SD), significant ANOVA in bold.

ANOVA p-Value

Effect Size

249.9 16.8

0.321

0.042

1.70 0.25

1.72 0.24

0.015

0.112

SH > HH

106.8 32.6

116.2 28.2

119.7 32.8

SS, SS < HH, SS < HS

456.2 137.6

501.4 161.1

547.4 167.1

558.8 151.9

< 0.001

0.479

SH < HH, SH < HS, SS < MM, SS < HH, SS < HS, MM < HH, MM < HS

10.2 4.9

9.4 5.0

10.5 4.9

10.5 4.3

9.9 4.8

0.020

0.102

SS < MM

41.6 6.4

41.0 6.7

41.2 6.2

41.3 5.9

40.9 6.5

0.246

0.049

SH

SS

MM

HH

HS

Sagittal Shoe Surface Angle [ ]

25.3 4.8

25.8 4.5

24.3 4.6

25.3 4.4

Plantar Flexion Velocity max [ /s]

913.4 61.0

933.5 69.4

936.2 63.5

Rearfoot Range of Motion [ ]

17.6 4.2

16.0 4.0

Pronation Velocity [ /s]

455.7 123.6

Knee Flexion Angle at Initial Contact [ ] Knee Flexion Angle max [ ]

Table 4. Perception variables (mean SD), significant ANOVA in bold. ANOVA p-Value

Effect Size

Post-hoc

7.2 2.9

p < 0.001

0.337

SH > MM, SH > HH, SH > HS, SS > HH, MM > HH, HH < HS

5.8 2.8

8.3 3.0

p < 0.001

0.321

SH > MM, SH > HH, SS > HH, MM > HH, HH < HS

8.7 2.9

6.8 2.5

8.4 3.0

p < 0.001

0.193

8.6 3.0

6.1 2.4

8.5 3.0

p < 0.001

0.288

SH

SS

MM

HH

HS

Cushioning Intensity [15 cm]

10.1 3.1

9.0 3.1

7.4 2.8

5.0 2.5

Cushioning Preference [15 cm]

10.5 3.0

9.7 3.3

8.4 2.7

Heel-Toe Transition [15 cm]

10.1 3.5

10.0 2.6

Overall Comfort [15 cm]

10.7 3.3

9.8 3.5

SH > HH, SS > HH SH > HH, SS > HH, MM > HH, HH < HS


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Figure 5. Perception variables as mean and standard deviation, repeated measures ANOVA significant for cushioning intensity (p < 0.001) and cushioning preference (p < 0.001), for significance of post-hoc shoe comparisons see Table 4.

natural as the characteristics of most of the applied variables are influenced right from the beginning of ground contact. An exception of this is resembled by peak vertical force II and maximum loading rate II. In general, maximum loading rate II was shown to be increased for shoe conditions having higher RF hardness. This suggests a transfer effect from RF heel strike which might influence the subsequent rollover characteristics. Although not significant, maximum loading rate II tended to be reduced for HS compared to HH and to be similar compared to MM, potentially indicating a reduction of loading characteristics of the second peak. In contrast, loading rate max II for SH did not increase at all compared to SS despite featuring a hard FF. Thus, a systematic behaviour of loading rate max II cannot be derived conclusively from this study. In general the amplitude and loading rate of the second vertical ground reaction force peak are considered to be largely influenced by the runner and only minimally by the shoe. Therefore, variables like peak vertical force II and loading rate max II are mostly ignored in biomechanical research. However, we felt right to analyse these variables in our study to extend the canon of common biomechanical variables by adding those variables representing more specifically the behaviour of the FF. Subjective results showed that the consistent cushioning conditions were rated according to their mechanical

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midsole hardness and impact characteristics. Participants perceived SS softer, MM in between, and HH harder with regard to shoe cushioning intensity. Regarding varied cushioning conditions, shoe condition SH was rated significantly softer compared to MM, HH, and HS. Cushioning of SH was rated similar to SS. These findings indicate that the soft RF dominated cushioning perception in contrast to the hard FF for the SH condition. Nevertheless, it is suggested that a soft RF and a relatively hard FF within one shoe condition may form a valuable shoe cushioning concept. Presumably such a shoe condition would provide a comfortable heel strike followed by a stable push-off. A previous perception study showed that heeltoe runners rated shoes with a hard forefoot, induced by the insole, as particularly uncomfortable (M€undermann et al., 2002). Our study now suggests that this is not necessarily the case if shoes featuring a hard FF are accompanied by a soft RF, as shown by the SH midsole characteristics. However, the discrepancy of the findings of these two studies may be explained by the different methodological approaches, on the one hand altering cushioning through the insole, which is placed right to the foot, and on the other hand altering cushioning by the midsole. The soft FF characteristics of HS affected participants’ cushioning intensity and preference perception considerably. Here a perception of a less hard, more preferred, and quite comfortable running shoe despite its hard RF was triggered. Cushioning preference ratings revealed that softer shoes were preferred over harder shoes, confirming earlier findings (M€undermann et al., 2002). Shoe conditions with soft RF (SH, SS) were perceived to exhibit smoother heel-toe transition only in comparison to HH, which was perceived to induce the least favourable rollover process. The soft RF midsole enabled smoother heel-toe transition perception than the harder RF midsole. However, as the general pattern of heel-toe transition ratings somehow reflected cushioning and comfort ratings, a connection between these subjective variables is likely, as also reported for various running shoe perception variables by Hennig (2011). The clear subjective discrimination of the experimental shoe conditions based solely on different cushioning characteristics underlines the importance of cushioning as an important feature of running shoes. In contrast to previous studies (De Wit et al., 1995; M€undermann et al., 2002; Hardin et al., 2004; Kersting & Br€uggemann, 2006; Nigg & Ge´rin-Lojoie, 2011), the hardness range of the experimental running shoes used in this study was rather narrow. Thereby, a specific reflection of shoe hardnesses of commercially available running shoes was achieved. Considering effects of FF cushioning, it was found that a hard FF did not change biomechanical and perception variables in shoes featuring a soft RF, whereas a soft FF compensated for inferior shoe perception attributed to shoes featuring a hard RF. These findings suggest that, in


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case a rather hard RF construction of running footwear is requested, a comparatively soft FF construction may be used to improve runners’ cushioning and comfort perception. Such findings may be related to foot anatomy and foot sensitivity characteristics of RF and FF. The FF with its more flexible and complex structure built of multiple bones, ligaments, joints, muscles, tendons and soft tissue, is able to accommodate for a harder FF by fine adjustments to external forces. Such adjustments are widely limited at the RF having a less complex anatomical structure, determined by only one bony structure, the calcaneus, and soft tissue. Perception ratings of this study refer to a comprehensive judgement of the whole stance phase of both the RF and FF. However, as the plantar FF was shown to be more sensitive to touch pressure stimuli compared to the RF (Hennig & Sterzing, 2009), one may assume that FF cushioning is particularly important for perceived comfort and of lesser importance for force reduction (Nigg, 2010). Follow-up studies should also examine whether runners can distinguish RF and FF hardness differences of midsole segments according to their actual mechanical properties. As the knee joint did not adjust to the different conditions, it is assumed not to play a noteworthy role in accommodating for the different midsole cushioning characteristics. This is most likely due to the narrow range of midsole hardness of the experimental shoe conditions, for which the foot and ankle complex adaptations were already suitable to provide sufficient shock attenuation. Here, harder RF characteristics increased angular velocities of plantar flexion and rearfoot pronation. For further discussion on this, the ground contact during heel-toe running is regarded as sequential procedure: Heel strike, foot unroll, foot flat, and push-off. Based on this, two perspectives are presented. The first suggests that the experimental shoe conditions are regarded as a purely mechanical interface, thereby influencing the roll over process of foot strike patterns on the basis of mechanical interaction only. A sequential pattern of heel-toe running with RF ground contact followed by FF ground contact needs to be considered, suggesting that there is a faster slapping mechanism in shoes having harder RF properties. The second perspective suggests that the experimental shoe conditions act like interfaces stimulating active foot strike alteration by adjustment of the runners’ biological system, predominantly at their lower extremities. Accordingly, as perception data revealed clear preferences for certain shoe conditions it is assumed that ground contact was actively modified. This effect is interpreted as an effort to achieve the most desirable running situation for a given shoe condition, which should be followed up on by application of muscle activity measurements prior and during ground contact. In addition to cushioning and comfort aspects during foot unroll, running efficiency should be considered with

modified midsole characteristics. Harder and denser midsoles may have increased the longitudinal bending stiffness of our running shoes, which featured only a plain flat outsole underneath the modified midsoles. Therefore, it is speculated that the harder shoes may have potential to increase running economy to some extent (Roy & Stefanyshyn, 2006). Although the total forefoot stiffness, as characterised by the interaction of foot and shoe, is dominated by the foot stiffness (Oleson et al., 2005), this probably illustrates the need for compromising between comfort and performance aspects of running shoes. 5. Conclusion This study reveals that runners are able to perceive differences in RF and FF cushioning characteristics of running shoe midsoles while biomechanically altered ground contact patterns occur. The examined biomechanical variables were largely dependent on running shoe RF characteristics, whereas runners’ perception was influenced by RF and, in part, by FF cushioning properties. Thus, a systematic consideration of interactive RF and FF cushioning could be of benefit for runners and shoe manufacturers. Follow-up research should focus on runners’ perception capacity to discriminate between posterior-anterior and also medio-lateral segmented cushion of running shoes. Individual preferences should be analyzed also with regard to subgroup populations (Schubert et al. 2011; Nigg et al., 2012). Acknowledgements We would like to thank Yuting Qin, Aiwen Wang and Bengang Yu for help during data collection, data processing, questionnaire translation, and subject interaction.

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