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Original research
Biomechanical variables and perception of comfort in running shoes with different cushioning technologies Roberto C. Dinato a , Ana P. Ribeiro a , Marco K. Butugan a , Ivye L.R. Pereira a , Andrea N. Onodera b , Isabel C.N. Sacco a,∗ a b
University of Sao Paulo, School of Medicine, Physical Therapy, Speech and Occupational Therapy Department, Brazil Biomechanics Laboratory, DASS Sport & Style Inc., Ivoti, Brazil
a r t i c l e
i n f o
Article history: Received 1 February 2013 Received in revised form 4 November 2013 Accepted 20 December 2013 Available online xxx Keywords: Plantar pressure Ground reaction force Comfort Running Biomechanics
a b s t r a c t Objectives: To investigate the relationships between the perception of comfort and biomechanical parameters (plantar pressure and ground reaction force) during running with four different types of cushioning technology in running shoes. Design: Randomized repeated measures. Methods: Twenty-two men, recreational runners (18–45 years) ran 12 km/h with running shoes with four different cushioning systems. Outcome measures included nine items related to perception of comfort and 12 biomechanical measures related to the ground reaction forces and plantar pressures. Repeated measure ANOVAs, Pearson correlation coefficients, and step-wise multiple regression analyses were employed (p ≤ 0.05). Results: No significant correlations were found between the perception of comfort and the biomechanical parameters for the four types of investigated shoes. Regression analysis revealed that 56% of the perceived general comfort can be explained by the variables push-off rate and pressure integral over the forefoot (p = 0.015) and that 33% of the perception of comfort over the forefoot can be explained by second peak force and push-off rate (p = 0.016). Conclusions: The results did not demonstrate significant relationships between the perception of comfort and the biomechanical parameters for the three types of shoes investigated (Gel, Air, and ethylene-vinyl acetate). Only the shoe with Adiprene+ technology had its general comfort and cushioning perception predicted by the loads over the forefoot. Thus, in general, one cannot predict the perception of comfort of a running shoe through impact and plantar pressure received. © 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction The popularity and the practice of running have considerably increased worldwide over the last 30 years.1–3 This has initiated much scientific interest for the development of new products and technologies to reduce potential risk factors of injuries associated with running, such as improvement of running shoes. Up until the1980s, research focusing on the development of running shoes adopted only approaches related to the results of mechanical tests of the shoes midsole materials. In addition to the mechanical tests usually performed, more complex biomechanical analyses were included with the purpose of developing better cushioning technologies after the 80s. The comprehension of how the body interacts with the running
∗ Corresponding author. E-mail address: [email protected] (I.C.N. Sacco).
shoes material, obtained by analyzing the resultant external forces produced by this interaction, was believed to be important for the development of specific technologies to attenuate the impact forces. The measurement of the ground reaction forces4 and the calculation of loading rates,5–7 both used as indirect methods for assessing these impacts during running, were found to be effective to identify how the these loads are attenuated by the use of various running shoes, and what is their relationship with histories of running injuries.7–9 In addition to the ground reaction force, measurement of plantar pressure appeared to be efficient in distinguishing differences between the characteristics of shoe cushioning,10 and thus, became a potential approach for the appropriate prescriptions of running shoes.11 Some researchers have recommended this approach to investigate the risk of running injuries.11,12 Recently, Clinghan et al.13 concluded from the measure of plantar pressures during gait, that the capacity of attenuating the loads was not related to the cost of the shoes. Considering that the indicators of impact,
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Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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measured by means of biomechanical approaches, could help the prescription of appropriate running shoes,11 it would be important to investigate if runners are capable of perceiving if the running shoes attenuates impact forces, similarly to the biomechanical assessments. These perceptions of comfort are closely related to the sense that the runners have regarding the loads imposed on their bodies during running practices. The perception of load attenuation (perception of cushioning) has been the focus of studies.14–16 Milani, Hennig, and Lafortune14 andHennig, Valiant, and Liu17 observed strong association between the runners’ perception of the shoe’s cushioning properties and the indicators of resultant impacts, assessed by ground reaction forces and plantar pressures, while using shoe with various ethylenevinyl acetate (EVA) midsole densities. Interestingly, based on these results, a better perception of cushioning was related to a higher magnitude of impact forces. Some authors suggested that the body perceptive–sensory systems are able to distinguish impacts of various frequencies and magnitudes, as a function of the characteristics of the shoe, particularly in the stiffness of their midsole. Thus, the runners adopted kinematic adjustments in their running techniques to reduce impact levels on the anatomical structures of their feet.14,17 It is important to note that previous studies13,16 only investigated how the different levels in stiffness of the EVA midsole altered the users’ perception and the biomechanical variables, and did not include nor specify the cushioning technologies of the running shoes. Wegener, Burns, and Penkala15 investigated in-shoe plantar pressure loading and comfort during running in two cushioning technologies running shoes, Gel and Hydro Flow only for athletes with cavus feet. Some technologies, such as air, gel, wave, amongst others, have been introduced in the midsole of the shoe with the purpose of optimizing the reductions of the impact forces. Therefore, it is important to conduct a biomechanical investigation that seeks potential relationships between the perception of impact modifications and load reductions in running shoes with technology cushioning midsoles. The objective of this study was to investigate the relationship between the perception of comfort and biomechanical variables related to impact during running with four different shoe cushioning technology types. The study’s hypotheses were: (i) running shoe with EVA midsole would lead to lower load rates, but lower levels of comfort; (ii) Gel, Air, and Adiprene shoes would result in lower load rates and higher levels of comfort, since the aggregate midsole materials would have the potential of optimizing load attenuation; and (iii) there would be significant correlations between rearfoot impacts and forefoot forces and the perception of comfort with these cushioning technology running shoes. 2. Methods Twenty two men, who were recreational runners with mean age of 39.4 ± 6.6 years; body mass of 76.1 ± 9.2 kg; height of 1.73 ± 0.04 m were evaluated, according to the following criteria:
Were aged between 18 and 45 years; had running experience of at least one year; a training volume of at least 20 km per week; a shoe size of 40; rearfoot contact running technique; a neutral static foot alignment, as determined by the Foot Posture Index-618 (FPI6), evaluated by a trained physiotherapist; and had not suffered any musculoskeletal injuries over the last six months. All participants provided written consent, based upon approval by the Ethics Committee of the School of Medicine of the University of Sao Paulo (329/11). All of the acquired running shoes were of known market brands, cost between (BRL 200–300), and to the characteristics of available shoes (Table 1). The shoes were masked with a black adhesive tape, so that any brand identification was eliminated, and were randomly numbered after being blinded, so neither the runners nor the examiners could identified them. In this way, the assessments of both comfort and biomechanical parameters were double blinded. Simple drawing randomized the order of assessments for each runner and this order was kept for the both comfort and biomechanical evaluations. The runners underwent a pre-trial adaptation phase for the each shoes for 10 min.17 Visual Analog Scale (VAS) evaluated the perception of comfort for each shoe characteristic evaluated. After each pre-trial adaptation, the runner rated nine aspects of the shoe related to its comfort perceived. The comfort scale used lengths 100 mm with the left end labeled ‘not comfortable at all’ (0 comfort point) and the right end ‘most comfortable condition imaginable’ (10 comfort points). Since many aspects of footwear may influence comfort, specific comfort ratings were included: forefoot cushioning, heel cushioning, arch height, heel height, shoe heel width, shoe forefoot width, shoe length, medio-lateral control and overall comfort, following Mundermann et al.19 study. The biomechanical measurement was carried out in two phases after the comfort evaluation. The first phase consisted of the acquisition of the plantar pressures during running on a flat asphalt surface at the University campus. The second phase consisted of measuring the ground reaction forces inside the laboratory. In both locations, the participants ran at 3.3 m/s (±5%) and were monitored by means of two photoelectrical sensors (Speed Test Fit Model, Nova Odessa, Brazil). The asphalt track was 40 m long and the plantar pressures were acquired in the intermediate 20 m. The plantar pressure was recorded at 100 Hz with the Pedar® in-shoe pressure measurement system (Novel, Munich, Germany), with a spatial resolution of approximately one sensor/cm.2 Three running trials were obtained for each shoe condition. The ground reaction forces were acquired with an AMTI force plate (AMTI OR-6-1000, Watertown, EUA) at 1 kHz. Before data acquisition, all participants were familiarized with the equipment, the laboratory setting, and the required speed. Nine valid trials were analyzed. The peak pressure (kPa), contact area (cm2 ), and the pressure time-integral (kPa s) were measured over three plantar areas: rearfoot (30% of foot length), midfoot (30% of foot length), and forefoot and toes (40% of foot length).20
Table 1 Specifications of the investigated footwear. Specifications
Air
Gel
Adiprene
EVA
Sole material Density of the rearfoot EVA (g/cm3 ) Impact absorption system on the rear and forefoot
Rubber 0.160
Rubber 0.153
Rubber 0.164
Rubber 0.238
Uretano-based chamber with capsulated gas under pressure Neutral 309
Adiprene in the rearfoot and Adiprene+ in the forefoot (viscous elastic foam) Neutral 322
EVA layers of various densities
Type of footstep Mass (g)
Gel cushioning units (silicon/polyurethane composite) Neutral 263
Neutral 320
EVA: ethylene-vinyl acetate.
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Five variables from the ground reaction force were analyzed: first peak force (body weight – BW), second peak (BW), loading rate 80 [N ms−1 ], defined as the force rate between 20 and 80% of the contact of the foot with the ground during the first peak; loading rate 100 [N ms−1 ], as determined by the force rate between 0 and 100% of the first peak; push-off rate [N ms−1 ], as defined as the rate of the second peak force, between the minimal values until the second peak. The force data were analyzed by a MatLab (version R2009a) routine, filtered with a fourth-order Butterworth filter with cut-off frequency of 30 Hz, and normalized by the body weight. All outcome measures showed normal distributions (Shapiro–Wilk test) and homogeneity of variances (Levene’s test). The 14 biomechanical variables (nine from plantar pressure and five from the ground reaction forces) and the VAS scores were compared between shoes using repeated measures ANOVAs, followed by Neuman–Keuls post hoc tests. Pearson correlation coefficients were calculated to investigate the relationship between the perception of comfort and the biomechanical variables for all shoes. The coefficients were classified as weak (r < 0.10); moderate (0.11 < r < 0.30); strong (0.31 < r < 0.60); and perfect (r > 0.60).21 For all analyses, we adopted p < 0.05. The 14 biomechanical variables were reduced and only those, whose correlation coefficients ≥0.20 entered into the model. Stepwise regression analyses were employed to determine which group of the biomechanical variables could best predict general running shoes comfort. The variables related to the rearfoot impact were also reduced to enter into the model to predict perceived of comfort over the rearfoot. Finally, the same procedures were applied to the variables related to push-off to enter the model to predict perceived of comfort over the forefoot.
The first peak force and the loading rate100 were 7.2 and 9.5%, respectively lower for the Adiprene, in relation to the Gel shoe. The Adiprene shoe demonstrated lower peak levels of pressure across the forefoot, in comparison with those of the Air (p < 0.001), Gel (p < 0.001), and EVA (p < 0.001), and lower integrals of pressure, when compared to those of the Air (p < 0.001), Gel (p < 0.001), and EVA (p < 0.001). Higher peak levels (p < 0.001) and integral of pressure (p < 0.001) were found for the EVA shoe, compared to those of all the others (Table 3). No significant correlations were found between the biomechanical variables and perception of comfort for the four investigated running shoes. The multiple linear regression analyses to predict general comfort reduced the number of variables to eight: Peak of pressure over the forefoot, integrals of pressure over the forefoot, contact areas over the forefoot, loading rate 80, loading rate 100, first and second peak forces, and push-off, based upon correlation coefficients ≥0.20. Only the model for the Adiprene shoe was significant (p = 0.015; R2 = 0.75; and R2 adjusted = 0.56. This model revealed that 56% of the perceived comfort was explained by the variables related to the push-off (ˇ = 0.62) and the integral of pressure over the forefoot (ˇ = 1.15). No significant differences were found for the other models. Regarding the regression models for the prediction of perception of comfort over the rearfoot and forefoot, the only one related to the perception of comfort over the forefoot for the Adiprene shoe was significant (p = 0.016; R2 = 0.63; and R2 adjusted = 0.33. This model revealed that 33% of the perception of comfort over the forefoot was explained by the second peak force (ˇ = −0.72) and push-off (ˇ = 0.77).
3. Results
This study attempted to identify the relationships between the perception of general comfort and biomechanical variables during running with shoes with four different cushioning technologies. In general, the results confirmed the first hypothesis and showed that the EVA shoe of various densities provided less comfort, independent of the shoes regions (forefoot and midfoot) and lower loading rate. Among the running shoes with impact cushioning technologies, the Adiprene provided the best comfort, independent of the shoes areas, and lower loading rate, confirming the second hypothesis. However, different from what was expected for
The EVA was significantly less comfortable compared to the other running shoes (p = 0.03). There were no significant differences between the shoes regarding the perception of comfort over the rearfoot and forefoot areas (p > 0.05) (Table 2). The highest first peak forces were observed for the Gel shoe, compared to those of the Air (p = 0.03) and Adiprene (p = 0.01). As shown in Table 2, the loading rate 100 were significantly lower for the Adiprene, in comparison with those of the Gel (p = 0.02).
4. Discussion
Table 2 Descriptive data (means ± SD) and comparisons between the four investigated footwear brands regarding vertical force variables and perception of comfort. pa
Variable
EVA
Ground reaction force 1st Vertical peak (BW) Loading rate 80 (N ms−1 ) Loading rate 100 (N ms−1 ) 2nd Vertical peak (BW) Push-off rate (N ms−1 )
1.88 67.1 53.4 2.5 15.8
± ± ± ± ±
0.3 15.8 11.0 0.2 2.3
1.94 69.6 56.2 2.5 15.2
± ± ± ± ±
0.3b,c 21.1 14.9c 0.2 3.2
1.81 65.7 51.3 2.5 15.6
± ± ± ± ±
0.3c 16.2 11.0c 0.2 2.9
1.84 70.5 54.5 2.5 16.0
± ± ± ± ±
0.3b 18.6 13.0 0.2 3.2
0.008 0.17 0.025 0.88 0.54
Comfort perception categories Heel cushioning Shoe heel width Heel height Forefoot cushioning Length of the shoe Shoe forefoot width Medio-lateral control Arch height Overall comfort
6.19 5.2 5.40 5.15 4.45 4.95 4.82 5.25 4.71
± ± ± ± ± ± ± ± ±
2.3 2.1d 2.3 2.8 2.5e 2.3 2.6e 2.0 2.5e
6.11 6.66 6.53 5.78 6.47 5.65 6.71 6.14 6.20
± ± ± ± ± ± ± ± ±
2.1 2.2c,d 2.1 2.6 2.6 2.5 2.0 2.5 2.7
6.59 6.71 6.65 5.91 6.42 5.55 6.7 6.71 6.82
± ± ± ± ± ± ± ± ±
1.6 1.9c 1.8 2.1 2.4 2.4 1.9 1.9 1.9
6.04 5.95 5.80 5.79 6.14 5.70 6.12 6.34 6.10
± ± ± ± ± ± ± ± ±
2.0 2.3 2.3 2.5 2.5 2.0 2.1 2.2 1.9
0.75 0.001 0.91 0.58 0.001 0.06 0.001 0.06 0.001
Gel
Adiprene
Air
EVA: ethylene-vinyl acetate; BW, body weight. a Repeated measure ANOVA. b Significant differences between the Air and Gel shoes. c Significant differences between the Gel and Adiprene shoes. d Significant differences between the Gel and EVA shoes. e EVA shoes different from all.
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Table 3 Descriptive data (means ± SD) and comparisons (F and p values) of the contact areas (cm2 ), peak pressures (kPa), and pressure-time integrals (kPa s) during running with the four investigated footwear brands. Plantar areas
Shoes
Area (cm2 )
Rearfoot
Air Gel Adiprene EVA Air Gel Adiprene EVA Air Gel Adiprene EVA
40.7 40.6 40.7 40.6 42.0 42.7 42.7 39.0 70.4 70.1 70.4 70.3
Midfoot
Forefoot
± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.5 0.3 0.4 3.3 2.7 2.3 4.7c 0.4 0.8 0.4 0.9
pe
Peak pressure (kPa)
F = 0.9; p = 0.47
242.7 239.5 246.5 303.0 126.2 141.7 136.2 124.3 313.1 306.7 279.1 314.8
F = 53.1; p < 0.001
F = 2.0; p = 0.11
± ± ± ± ± ± ± ± ± ± ± ±
40.8 40.0 51.6 54.2c 32.9f,g 38.0f,i 28.5g,j 38.1i,j 54.9 63.9 56.8b 68.2
pe
Pressure-time integral (kPa s)
F = 141; p < 0.001
18.2 18.3 18.2 21.6 16.6 18.7 17.8 15.2 44.4 43.3 39.0 43.1
F = 16.8; p < 0,.01
F = 33.7; p < 0.001
± ± ± ± ± ± ± ± ± ± ± ±
3.0 4.1 3.5 3.6c 5.3 5.7d 4.8b 5.9 8.2a 8.0 7.7b 9.1
pe F = 32.9; p < 0.001
F = 28.6; p < 0.001
F = 49.7; p < 0.001
EVA: ethylene-vinyl acetate. a Means that the air shoe were significantly different from the others. b The adiprene shoe was different from the others. c The EVA shoe was different from the others. d The Gel shoe was different from the others. e Repeated measure ANOVAs. f Significant differences between the Air and Gel shoes; g Significant differences between the Air and Adiprene shoes; h Significant differences between the Gel and Adiprene shoes; i Significant differences between the Gel and EVA shoes; j Significant differences between the Adiprene and EVA shoes.
the third hypothesis, there were no significant correlations found between the perception of comfort and the biomechanical variables for any of the investigated running shoes. Fifty-six percent of the general comfort was predicted by two variables, the pushoff and the integrals of pressures, and 33% of the perception of comfort over the forefoot was predicted by the push-offand the second peak force, but only for the Adiprene+ technology running shoe. The general comfort perceived by the runners was not different between the running shoes with the addition of cushioning impact technologies (Gel, Air, and Adiprene). A possible explanation for this result could be their comparable sole characteristics, whose densities were similar to those of the EVA shoes (gel: 0.153 g/cm3 ; air: 0.160 g/cm3 , and adiprene: 0.164 g/cm3 ). The greater levels of rigidity of the sole of the EVA shoe may have generated greater discomfort for the runners. Another important factor that may have influenced the perception of comfort of the EVA midsole with various densities were the lower levels of comfort regarding medium–lateral control, which could have changed the contact areas of the feet inside the running shoe and, consequently, altered the proprioceptive perception of these runners, which resulted in general feelings of discomfort. The results showed that none of the impact-related variables were related to the perception of general comfort. Only two previous studies demonstrated relationships between perception of cushioning and biomechanical variables.14,17 Both Milani, Hennig, and Lafortune14 and Hennig, Valiant, and Liu17 reported significant relationships between the perception of cushioning and variables related to the ground reaction forces and plantar pressures during running with predominantly EVA shoe with different densities of the soles. Both studies found lower loading rates in stiffer shoes. In the present study, these relationships held true only for the EVA-based technology shoe, but not for the others, even with the addition of material to the midsole to optimize load reductions. However, these types ofrunning shoes were not studied by Milani, Hennig, and Lafortune14 and Hennig, Valiant, and Liu.17 Therefore, these materials inserted in the midsoles as impact reduction technologies changed the relationships between the biomechanical responses and the perception that the runners had regarding cushioning capacity and general comfort of the running shoes.
Chen and Nigg22 showed that the integral and the peak of pressure variables were sensitive to detect differences in comfort, when the effects of insoles were evaluated during gait, but not during running. Wegener, Burns, and Penkala15 also did not find any relationships between the general comfort of the running shoes and the plantar pressures with runners with cavus feet. Jordan, Payton, and Bartlett23 also did not observe any relationships between measures of pressure and perception of comfort in 15 participants who walked with a variety of usual footwear. Although comfort is an important factor for the purchase of running shoes, the present results, added to the inconsistent findings in the literature, still does not elucidate how the comfort or the perception of cushioning of the running shoes could be associated with impact-related biomechanical variables. A better explanation of these relationships could bring benefits for the design of running shoes for the improvement of comfort and decreased loading rates during running. Another interesting finding of this study was the prediction of general comfort by the push-off and the integral of pressure variables, and the prediction of the perception of comfort over the forefoot by the push-off and the second vertical peak force variables. However, these predictors were observed only for the Adiprene technology, which was also evaluated by the runners as of greater comfort and softness. This technology had also lower density of the sole, which was similar to the Air and Gel shoes, differing from the EVA technology, which was evaluated as of lower comfort, greater rigidity, and a higher density of the sole. Contrary to the present findings, Hennig, Valiant, and Liu17 found higher peaks of pressure over the heel and higher loading rates in softer shoes, compared to harder products. Milani, Hennig, and Lafortune14 also observed that the greater the cushioning, the higher were the loading rates. Both findings reported by Hennig, Valiant, and Liu17 and Milani, Hennig, and Lafortune14 supported the idea that based upon the runners’ perception, there is an adaptation of their techniques with stiffer footwear which avoids high impact rates over the heel. The present results indicated that based upon these abilities, these adaptations did not occur only with stiffer footwear, but also with softer ones, since the evaluated footwear were not comparable regarding the biomechanical variables. Nurse et al.24 demonstrated that the changes of the texture of footwear provoked changes in kinematic gait patterns.
Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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In this way, the differences of the designs and technologies of the evaluated running shoes could have generated subtle kinematic adjustments during running to the point of masking the differences of the impact, or variables that were measured in the shoe–foot interface. In summary, depending upon cushioning technology, the running shoes with better perception of comfort and softness also could generate lower loading rates. However, it was not possible to infer that the results found for the Adiprene technology could be reproduced in other market technologies. It should be noted that only four technologies of running shoes within multiple possibilities were evaluated, therefore, caution should be taken when transferring the present results to other technologies, even if they seem similar. A limitation of this study was that other structural elements of the running shoes, which could interfere with the perception of comfort, such as the types of sewing and the number of fabrics utilized in the design, were not evaluated. Additionally, because the running shoe’s size available was only 40, it was difficult to include women in the study. Our conclusions are also restricted to runners with rearfoot strike pattern. Future research involving the relationships between comfort and biomechanical variables should consider these design characteristics.
5. Conclusions The findings of the present study did not show significant associations between the biomechanical variables and the perception of comfort for three of the four different cushioning technologies (Gel, Air, and EVA with various densities). Only for the Adiprene technology running shoes, the general comfort and the perception of comfort were predicted by the loading rates over the forefoot. Thus, in general, it is not possible to predict general comfort of running shoes by means of received impacts and pressures.
6. Practical implications • High load rates have been associated with the risk of some injuries in recreational runners, however, the choice of running shoes should not be based solely upon perception of comfort, but upon the technology of the sole of the shoes, which provides lower loading rates. • None of the four cushioning technologies of the investigated running shoes resulted in substantial differences regarding the biomechanical variables. The technology which generated the lower impacts did not show any relationships with the perceived comfort. • Both the running shoes with the best and worse perception of comfort resulted in lower loading rates. All the investigated technologies demonstrated similar characteristics in reducing the impact during running.
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Acknowledgments The authors acknowledge the Brazilian Government Funding Agencies: State of Sao Paulo Research Foundation (FAPESP) and Coordination for the Improvement of Higher Level Personnel (CAPES). We attest that we do not have any conflict of interest with any footwear company. The shoes were purchased by the laboratory that performed the study. References 1. Tillman MD, Fiolkowski P, Bauer JA et al. In-shoe plantar measurements during running on different surfaces. Sports Eng 2002; 5:121–128. 2. Feehery RV. The biomechanics of running on different surfaces. Clin Podiatr Med Surg 1986; 3(4):649–659. 3. Novacheck TF. The biomechanics of running. Gait Posture 1998; 7(1):77–95. 4. Lieberman DE, Venkadesan M, Werbel WA et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 2010; 463(7280):531–535. 5. Pohl MB, Hamill J, Davis IS. Biomechanical and anatomic factors associated with a history of plantar fasciitis in female runners. Clin J Sport Med 2009; 19(5):372–376. 6. Crowell HP, Davis IS. Gait retraining to reduce lower extremity loading in runners. Clin Biomech (Bristol, Avon) 2011; 26(1):78–83. 7. Milner CE, Ferber R, Pollard CD et al. Biomechanical factors associated with tibial stress fracture in female runners. Med Sci Sports Exerc 2006; 38(2):323–328. 8. Radin EL, Yang KH, Riegger C et al. Relationship between lower limb dynamics and knee joint pain. J Orthop Res 1991; 9(3):398–405. 9. Bredeweg SW, Kluitenberg B, Bessem B et al. Differences in kinetic variables between injured and noninjured novice runners: A prospective cohort study. J Sci Med Sport 2012. 10. Verdejo R, Mills NJ. Heel-shoe interactions and the durability of EVA foam running-shoe midsoles. J Biomech 2004; 37(9):1379–1386. 11. Dixon SJ. Use of pressure insoles to compare in-shoe loading for modern running shoes. Ergonomics 2008; 51(10):1503–1514. 12. Hennig EM, Milani TL. Pressure distribution measurements for evaluation of running shoe properties. Sportverletz Sportschaden 2000; 14(3):90–97. 13. Clinghan R, Arnold GP, Drew TS et al. Do you get value for money when you buy an expensive pair of running shoes? Br J Sports Med 2008; 42(3):189–193. 14. Milani TL, Hennig EM, Lafortune MA. Perceptual and biomechanical variables for running in identical shoe constructions with varying midsole hardness. Clin Biomech (Bristol, Avon) 1997; 12(5):294–300. 15. Wegener C, Burns J, Penkala S. Effect of neutral-cushioned running shoes on plantar pressure loading and comfort in athletes with cavus feet: a crossover randomized controlled trial. Am J Sports Med 2008; 36(11):2139–2146. 16. Mündermann A, Stefanyshyn DJ, Nigg BM. Relationship between footwear comfort of shoe inserts and anthropometric and sensory factors. Med Sci Sports Exerc 2001; 33(11):1939–1945. 17. Hennig EM, Valiant GA, Liu Q. Biomechanical variables and the perception of cushioning for running in various types of footwear. J Appl Biomech 1996; 12(2):143–150. 18. Redmond AC, Crosbie J, Ouvrier RA. Development and validation of a novel rating system for scoring standing foot posture: the Foot Posture Index. Clin Biomech (Bristol Avon) 2006; 21(1):89–98. 19. Mündermann A, Nigg BM, Stefanyshyn DJ et al. Development of a reliable method to assess footwear comfort during running. Gait Posture 2002; 16(1):38–45. 20. Ribeiro AP, Trombini-Souza F, Tessutti VD et al. The effects of plantar fasciitis and pain on plantar pressure distribution of recreational runners. Clin Biomech (Bristol, Avon) 2011; 26(2):194–199. 21. Levin J, Fox JA, Brazil Estatística para ciências humanas, 2004. 22. Chen H, Nigg BM. Relationship between plantar pressure distribution under the foot and insole comfort. Clin Biomech 1994; 9:335–341. 23. Jordan C, Payton C, Bartlett R. Perceived comfort and pressure distribution in casual footwear. Clin Biomech (Bristol, Avon) 1997; 12(3):S5. 24. Nurse MA, Hulliger M, Wakeling JM et al. Changing the texture of footwear can alter gait patterns. J Electromyogr Kinesiol 2005; 15(5):496–506.
Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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Journal of Science and Medicine in Sport xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Science and Medicine in Sport journal homepage: www.elsevier.com/locate/jsams
Original research
Biomechanical variables and perception of comfort in running shoes with different cushioning technologies Roberto C. Dinato a , Ana P. Ribeiro a , Marco K. Butugan a , Ivye L.R. Pereira a , Andrea N. Onodera b , Isabel C.N. Sacco a,∗ a b
University of Sao Paulo, School of Medicine, Physical Therapy, Speech and Occupational Therapy Department, Brazil Biomechanics Laboratory, DASS Sport & Style Inc., Ivoti, Brazil
a r t i c l e
i n f o
Article history: Received 1 February 2013 Received in revised form 4 November 2013 Accepted 20 December 2013 Available online xxx Keywords: Plantar pressure Ground reaction force Comfort Running Biomechanics
a b s t r a c t Objectives: To investigate the relationships between the perception of comfort and biomechanical parameters (plantar pressure and ground reaction force) during running with four different types of cushioning technology in running shoes. Design: Randomized repeated measures. Methods: Twenty-two men, recreational runners (18–45 years) ran 12 km/h with running shoes with four different cushioning systems. Outcome measures included nine items related to perception of comfort and 12 biomechanical measures related to the ground reaction forces and plantar pressures. Repeated measure ANOVAs, Pearson correlation coefficients, and step-wise multiple regression analyses were employed (p ≤ 0.05). Results: No significant correlations were found between the perception of comfort and the biomechanical parameters for the four types of investigated shoes. Regression analysis revealed that 56% of the perceived general comfort can be explained by the variables push-off rate and pressure integral over the forefoot (p = 0.015) and that 33% of the perception of comfort over the forefoot can be explained by second peak force and push-off rate (p = 0.016). Conclusions: The results did not demonstrate significant relationships between the perception of comfort and the biomechanical parameters for the three types of shoes investigated (Gel, Air, and ethylene-vinyl acetate). Only the shoe with Adiprene+ technology had its general comfort and cushioning perception predicted by the loads over the forefoot. Thus, in general, one cannot predict the perception of comfort of a running shoe through impact and plantar pressure received. © 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction The popularity and the practice of running have considerably increased worldwide over the last 30 years.1–3 This has initiated much scientific interest for the development of new products and technologies to reduce potential risk factors of injuries associated with running, such as improvement of running shoes. Up until the1980s, research focusing on the development of running shoes adopted only approaches related to the results of mechanical tests of the shoes midsole materials. In addition to the mechanical tests usually performed, more complex biomechanical analyses were included with the purpose of developing better cushioning technologies after the 80s. The comprehension of how the body interacts with the running
∗ Corresponding author. E-mail address: [email protected] (I.C.N. Sacco).
shoes material, obtained by analyzing the resultant external forces produced by this interaction, was believed to be important for the development of specific technologies to attenuate the impact forces. The measurement of the ground reaction forces4 and the calculation of loading rates,5–7 both used as indirect methods for assessing these impacts during running, were found to be effective to identify how the these loads are attenuated by the use of various running shoes, and what is their relationship with histories of running injuries.7–9 In addition to the ground reaction force, measurement of plantar pressure appeared to be efficient in distinguishing differences between the characteristics of shoe cushioning,10 and thus, became a potential approach for the appropriate prescriptions of running shoes.11 Some researchers have recommended this approach to investigate the risk of running injuries.11,12 Recently, Clinghan et al.13 concluded from the measure of plantar pressures during gait, that the capacity of attenuating the loads was not related to the cost of the shoes. Considering that the indicators of impact,
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Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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measured by means of biomechanical approaches, could help the prescription of appropriate running shoes,11 it would be important to investigate if runners are capable of perceiving if the running shoes attenuates impact forces, similarly to the biomechanical assessments. These perceptions of comfort are closely related to the sense that the runners have regarding the loads imposed on their bodies during running practices. The perception of load attenuation (perception of cushioning) has been the focus of studies.14–16 Milani, Hennig, and Lafortune14 andHennig, Valiant, and Liu17 observed strong association between the runners’ perception of the shoe’s cushioning properties and the indicators of resultant impacts, assessed by ground reaction forces and plantar pressures, while using shoe with various ethylenevinyl acetate (EVA) midsole densities. Interestingly, based on these results, a better perception of cushioning was related to a higher magnitude of impact forces. Some authors suggested that the body perceptive–sensory systems are able to distinguish impacts of various frequencies and magnitudes, as a function of the characteristics of the shoe, particularly in the stiffness of their midsole. Thus, the runners adopted kinematic adjustments in their running techniques to reduce impact levels on the anatomical structures of their feet.14,17 It is important to note that previous studies13,16 only investigated how the different levels in stiffness of the EVA midsole altered the users’ perception and the biomechanical variables, and did not include nor specify the cushioning technologies of the running shoes. Wegener, Burns, and Penkala15 investigated in-shoe plantar pressure loading and comfort during running in two cushioning technologies running shoes, Gel and Hydro Flow only for athletes with cavus feet. Some technologies, such as air, gel, wave, amongst others, have been introduced in the midsole of the shoe with the purpose of optimizing the reductions of the impact forces. Therefore, it is important to conduct a biomechanical investigation that seeks potential relationships between the perception of impact modifications and load reductions in running shoes with technology cushioning midsoles. The objective of this study was to investigate the relationship between the perception of comfort and biomechanical variables related to impact during running with four different shoe cushioning technology types. The study’s hypotheses were: (i) running shoe with EVA midsole would lead to lower load rates, but lower levels of comfort; (ii) Gel, Air, and Adiprene shoes would result in lower load rates and higher levels of comfort, since the aggregate midsole materials would have the potential of optimizing load attenuation; and (iii) there would be significant correlations between rearfoot impacts and forefoot forces and the perception of comfort with these cushioning technology running shoes. 2. Methods Twenty two men, who were recreational runners with mean age of 39.4 ± 6.6 years; body mass of 76.1 ± 9.2 kg; height of 1.73 ± 0.04 m were evaluated, according to the following criteria:
Were aged between 18 and 45 years; had running experience of at least one year; a training volume of at least 20 km per week; a shoe size of 40; rearfoot contact running technique; a neutral static foot alignment, as determined by the Foot Posture Index-618 (FPI6), evaluated by a trained physiotherapist; and had not suffered any musculoskeletal injuries over the last six months. All participants provided written consent, based upon approval by the Ethics Committee of the School of Medicine of the University of Sao Paulo (329/11). All of the acquired running shoes were of known market brands, cost between (BRL 200–300), and to the characteristics of available shoes (Table 1). The shoes were masked with a black adhesive tape, so that any brand identification was eliminated, and were randomly numbered after being blinded, so neither the runners nor the examiners could identified them. In this way, the assessments of both comfort and biomechanical parameters were double blinded. Simple drawing randomized the order of assessments for each runner and this order was kept for the both comfort and biomechanical evaluations. The runners underwent a pre-trial adaptation phase for the each shoes for 10 min.17 Visual Analog Scale (VAS) evaluated the perception of comfort for each shoe characteristic evaluated. After each pre-trial adaptation, the runner rated nine aspects of the shoe related to its comfort perceived. The comfort scale used lengths 100 mm with the left end labeled ‘not comfortable at all’ (0 comfort point) and the right end ‘most comfortable condition imaginable’ (10 comfort points). Since many aspects of footwear may influence comfort, specific comfort ratings were included: forefoot cushioning, heel cushioning, arch height, heel height, shoe heel width, shoe forefoot width, shoe length, medio-lateral control and overall comfort, following Mundermann et al.19 study. The biomechanical measurement was carried out in two phases after the comfort evaluation. The first phase consisted of the acquisition of the plantar pressures during running on a flat asphalt surface at the University campus. The second phase consisted of measuring the ground reaction forces inside the laboratory. In both locations, the participants ran at 3.3 m/s (±5%) and were monitored by means of two photoelectrical sensors (Speed Test Fit Model, Nova Odessa, Brazil). The asphalt track was 40 m long and the plantar pressures were acquired in the intermediate 20 m. The plantar pressure was recorded at 100 Hz with the Pedar® in-shoe pressure measurement system (Novel, Munich, Germany), with a spatial resolution of approximately one sensor/cm.2 Three running trials were obtained for each shoe condition. The ground reaction forces were acquired with an AMTI force plate (AMTI OR-6-1000, Watertown, EUA) at 1 kHz. Before data acquisition, all participants were familiarized with the equipment, the laboratory setting, and the required speed. Nine valid trials were analyzed. The peak pressure (kPa), contact area (cm2 ), and the pressure time-integral (kPa s) were measured over three plantar areas: rearfoot (30% of foot length), midfoot (30% of foot length), and forefoot and toes (40% of foot length).20
Table 1 Specifications of the investigated footwear. Specifications
Air
Gel
Adiprene
EVA
Sole material Density of the rearfoot EVA (g/cm3 ) Impact absorption system on the rear and forefoot
Rubber 0.160
Rubber 0.153
Rubber 0.164
Rubber 0.238
Uretano-based chamber with capsulated gas under pressure Neutral 309
Adiprene in the rearfoot and Adiprene+ in the forefoot (viscous elastic foam) Neutral 322
EVA layers of various densities
Type of footstep Mass (g)
Gel cushioning units (silicon/polyurethane composite) Neutral 263
Neutral 320
EVA: ethylene-vinyl acetate.
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Five variables from the ground reaction force were analyzed: first peak force (body weight – BW), second peak (BW), loading rate 80 [N ms−1 ], defined as the force rate between 20 and 80% of the contact of the foot with the ground during the first peak; loading rate 100 [N ms−1 ], as determined by the force rate between 0 and 100% of the first peak; push-off rate [N ms−1 ], as defined as the rate of the second peak force, between the minimal values until the second peak. The force data were analyzed by a MatLab (version R2009a) routine, filtered with a fourth-order Butterworth filter with cut-off frequency of 30 Hz, and normalized by the body weight. All outcome measures showed normal distributions (Shapiro–Wilk test) and homogeneity of variances (Levene’s test). The 14 biomechanical variables (nine from plantar pressure and five from the ground reaction forces) and the VAS scores were compared between shoes using repeated measures ANOVAs, followed by Neuman–Keuls post hoc tests. Pearson correlation coefficients were calculated to investigate the relationship between the perception of comfort and the biomechanical variables for all shoes. The coefficients were classified as weak (r < 0.10); moderate (0.11 < r < 0.30); strong (0.31 < r < 0.60); and perfect (r > 0.60).21 For all analyses, we adopted p < 0.05. The 14 biomechanical variables were reduced and only those, whose correlation coefficients ≥0.20 entered into the model. Stepwise regression analyses were employed to determine which group of the biomechanical variables could best predict general running shoes comfort. The variables related to the rearfoot impact were also reduced to enter into the model to predict perceived of comfort over the rearfoot. Finally, the same procedures were applied to the variables related to push-off to enter the model to predict perceived of comfort over the forefoot.
The first peak force and the loading rate100 were 7.2 and 9.5%, respectively lower for the Adiprene, in relation to the Gel shoe. The Adiprene shoe demonstrated lower peak levels of pressure across the forefoot, in comparison with those of the Air (p < 0.001), Gel (p < 0.001), and EVA (p < 0.001), and lower integrals of pressure, when compared to those of the Air (p < 0.001), Gel (p < 0.001), and EVA (p < 0.001). Higher peak levels (p < 0.001) and integral of pressure (p < 0.001) were found for the EVA shoe, compared to those of all the others (Table 3). No significant correlations were found between the biomechanical variables and perception of comfort for the four investigated running shoes. The multiple linear regression analyses to predict general comfort reduced the number of variables to eight: Peak of pressure over the forefoot, integrals of pressure over the forefoot, contact areas over the forefoot, loading rate 80, loading rate 100, first and second peak forces, and push-off, based upon correlation coefficients ≥0.20. Only the model for the Adiprene shoe was significant (p = 0.015; R2 = 0.75; and R2 adjusted = 0.56. This model revealed that 56% of the perceived comfort was explained by the variables related to the push-off (ˇ = 0.62) and the integral of pressure over the forefoot (ˇ = 1.15). No significant differences were found for the other models. Regarding the regression models for the prediction of perception of comfort over the rearfoot and forefoot, the only one related to the perception of comfort over the forefoot for the Adiprene shoe was significant (p = 0.016; R2 = 0.63; and R2 adjusted = 0.33. This model revealed that 33% of the perception of comfort over the forefoot was explained by the second peak force (ˇ = −0.72) and push-off (ˇ = 0.77).
3. Results
This study attempted to identify the relationships between the perception of general comfort and biomechanical variables during running with shoes with four different cushioning technologies. In general, the results confirmed the first hypothesis and showed that the EVA shoe of various densities provided less comfort, independent of the shoes regions (forefoot and midfoot) and lower loading rate. Among the running shoes with impact cushioning technologies, the Adiprene provided the best comfort, independent of the shoes areas, and lower loading rate, confirming the second hypothesis. However, different from what was expected for
The EVA was significantly less comfortable compared to the other running shoes (p = 0.03). There were no significant differences between the shoes regarding the perception of comfort over the rearfoot and forefoot areas (p > 0.05) (Table 2). The highest first peak forces were observed for the Gel shoe, compared to those of the Air (p = 0.03) and Adiprene (p = 0.01). As shown in Table 2, the loading rate 100 were significantly lower for the Adiprene, in comparison with those of the Gel (p = 0.02).
4. Discussion
Table 2 Descriptive data (means ± SD) and comparisons between the four investigated footwear brands regarding vertical force variables and perception of comfort. pa
Variable
EVA
Ground reaction force 1st Vertical peak (BW) Loading rate 80 (N ms−1 ) Loading rate 100 (N ms−1 ) 2nd Vertical peak (BW) Push-off rate (N ms−1 )
1.88 67.1 53.4 2.5 15.8
± ± ± ± ±
0.3 15.8 11.0 0.2 2.3
1.94 69.6 56.2 2.5 15.2
± ± ± ± ±
0.3b,c 21.1 14.9c 0.2 3.2
1.81 65.7 51.3 2.5 15.6
± ± ± ± ±
0.3c 16.2 11.0c 0.2 2.9
1.84 70.5 54.5 2.5 16.0
± ± ± ± ±
0.3b 18.6 13.0 0.2 3.2
0.008 0.17 0.025 0.88 0.54
Comfort perception categories Heel cushioning Shoe heel width Heel height Forefoot cushioning Length of the shoe Shoe forefoot width Medio-lateral control Arch height Overall comfort
6.19 5.2 5.40 5.15 4.45 4.95 4.82 5.25 4.71
± ± ± ± ± ± ± ± ±
2.3 2.1d 2.3 2.8 2.5e 2.3 2.6e 2.0 2.5e
6.11 6.66 6.53 5.78 6.47 5.65 6.71 6.14 6.20
± ± ± ± ± ± ± ± ±
2.1 2.2c,d 2.1 2.6 2.6 2.5 2.0 2.5 2.7
6.59 6.71 6.65 5.91 6.42 5.55 6.7 6.71 6.82
± ± ± ± ± ± ± ± ±
1.6 1.9c 1.8 2.1 2.4 2.4 1.9 1.9 1.9
6.04 5.95 5.80 5.79 6.14 5.70 6.12 6.34 6.10
± ± ± ± ± ± ± ± ±
2.0 2.3 2.3 2.5 2.5 2.0 2.1 2.2 1.9
0.75 0.001 0.91 0.58 0.001 0.06 0.001 0.06 0.001
Gel
Adiprene
Air
EVA: ethylene-vinyl acetate; BW, body weight. a Repeated measure ANOVA. b Significant differences between the Air and Gel shoes. c Significant differences between the Gel and Adiprene shoes. d Significant differences between the Gel and EVA shoes. e EVA shoes different from all.
Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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Table 3 Descriptive data (means ± SD) and comparisons (F and p values) of the contact areas (cm2 ), peak pressures (kPa), and pressure-time integrals (kPa s) during running with the four investigated footwear brands. Plantar areas
Shoes
Area (cm2 )
Rearfoot
Air Gel Adiprene EVA Air Gel Adiprene EVA Air Gel Adiprene EVA
40.7 40.6 40.7 40.6 42.0 42.7 42.7 39.0 70.4 70.1 70.4 70.3
Midfoot
Forefoot
± ± ± ± ± ± ± ± ± ± ± ±
0.3 0.5 0.3 0.4 3.3 2.7 2.3 4.7c 0.4 0.8 0.4 0.9
pe
Peak pressure (kPa)
F = 0.9; p = 0.47
242.7 239.5 246.5 303.0 126.2 141.7 136.2 124.3 313.1 306.7 279.1 314.8
F = 53.1; p < 0.001
F = 2.0; p = 0.11
± ± ± ± ± ± ± ± ± ± ± ±
40.8 40.0 51.6 54.2c 32.9f,g 38.0f,i 28.5g,j 38.1i,j 54.9 63.9 56.8b 68.2
pe
Pressure-time integral (kPa s)
F = 141; p < 0.001
18.2 18.3 18.2 21.6 16.6 18.7 17.8 15.2 44.4 43.3 39.0 43.1
F = 16.8; p < 0,.01
F = 33.7; p < 0.001
± ± ± ± ± ± ± ± ± ± ± ±
3.0 4.1 3.5 3.6c 5.3 5.7d 4.8b 5.9 8.2a 8.0 7.7b 9.1
pe F = 32.9; p < 0.001
F = 28.6; p < 0.001
F = 49.7; p < 0.001
EVA: ethylene-vinyl acetate. a Means that the air shoe were significantly different from the others. b The adiprene shoe was different from the others. c The EVA shoe was different from the others. d The Gel shoe was different from the others. e Repeated measure ANOVAs. f Significant differences between the Air and Gel shoes; g Significant differences between the Air and Adiprene shoes; h Significant differences between the Gel and Adiprene shoes; i Significant differences between the Gel and EVA shoes; j Significant differences between the Adiprene and EVA shoes.
the third hypothesis, there were no significant correlations found between the perception of comfort and the biomechanical variables for any of the investigated running shoes. Fifty-six percent of the general comfort was predicted by two variables, the pushoff and the integrals of pressures, and 33% of the perception of comfort over the forefoot was predicted by the push-offand the second peak force, but only for the Adiprene+ technology running shoe. The general comfort perceived by the runners was not different between the running shoes with the addition of cushioning impact technologies (Gel, Air, and Adiprene). A possible explanation for this result could be their comparable sole characteristics, whose densities were similar to those of the EVA shoes (gel: 0.153 g/cm3 ; air: 0.160 g/cm3 , and adiprene: 0.164 g/cm3 ). The greater levels of rigidity of the sole of the EVA shoe may have generated greater discomfort for the runners. Another important factor that may have influenced the perception of comfort of the EVA midsole with various densities were the lower levels of comfort regarding medium–lateral control, which could have changed the contact areas of the feet inside the running shoe and, consequently, altered the proprioceptive perception of these runners, which resulted in general feelings of discomfort. The results showed that none of the impact-related variables were related to the perception of general comfort. Only two previous studies demonstrated relationships between perception of cushioning and biomechanical variables.14,17 Both Milani, Hennig, and Lafortune14 and Hennig, Valiant, and Liu17 reported significant relationships between the perception of cushioning and variables related to the ground reaction forces and plantar pressures during running with predominantly EVA shoe with different densities of the soles. Both studies found lower loading rates in stiffer shoes. In the present study, these relationships held true only for the EVA-based technology shoe, but not for the others, even with the addition of material to the midsole to optimize load reductions. However, these types ofrunning shoes were not studied by Milani, Hennig, and Lafortune14 and Hennig, Valiant, and Liu.17 Therefore, these materials inserted in the midsoles as impact reduction technologies changed the relationships between the biomechanical responses and the perception that the runners had regarding cushioning capacity and general comfort of the running shoes.
Chen and Nigg22 showed that the integral and the peak of pressure variables were sensitive to detect differences in comfort, when the effects of insoles were evaluated during gait, but not during running. Wegener, Burns, and Penkala15 also did not find any relationships between the general comfort of the running shoes and the plantar pressures with runners with cavus feet. Jordan, Payton, and Bartlett23 also did not observe any relationships between measures of pressure and perception of comfort in 15 participants who walked with a variety of usual footwear. Although comfort is an important factor for the purchase of running shoes, the present results, added to the inconsistent findings in the literature, still does not elucidate how the comfort or the perception of cushioning of the running shoes could be associated with impact-related biomechanical variables. A better explanation of these relationships could bring benefits for the design of running shoes for the improvement of comfort and decreased loading rates during running. Another interesting finding of this study was the prediction of general comfort by the push-off and the integral of pressure variables, and the prediction of the perception of comfort over the forefoot by the push-off and the second vertical peak force variables. However, these predictors were observed only for the Adiprene technology, which was also evaluated by the runners as of greater comfort and softness. This technology had also lower density of the sole, which was similar to the Air and Gel shoes, differing from the EVA technology, which was evaluated as of lower comfort, greater rigidity, and a higher density of the sole. Contrary to the present findings, Hennig, Valiant, and Liu17 found higher peaks of pressure over the heel and higher loading rates in softer shoes, compared to harder products. Milani, Hennig, and Lafortune14 also observed that the greater the cushioning, the higher were the loading rates. Both findings reported by Hennig, Valiant, and Liu17 and Milani, Hennig, and Lafortune14 supported the idea that based upon the runners’ perception, there is an adaptation of their techniques with stiffer footwear which avoids high impact rates over the heel. The present results indicated that based upon these abilities, these adaptations did not occur only with stiffer footwear, but also with softer ones, since the evaluated footwear were not comparable regarding the biomechanical variables. Nurse et al.24 demonstrated that the changes of the texture of footwear provoked changes in kinematic gait patterns.
Please cite this article in press as: Dinato RC, et al. Biomechanical variables and perception of comfort in running shoes with different cushioning technologies. J Sci Med Sport (2014), http://dx.doi.org/10.1016/j.jsams.2013.12.003
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In this way, the differences of the designs and technologies of the evaluated running shoes could have generated subtle kinematic adjustments during running to the point of masking the differences of the impact, or variables that were measured in the shoe–foot interface. In summary, depending upon cushioning technology, the running shoes with better perception of comfort and softness also could generate lower loading rates. However, it was not possible to infer that the results found for the Adiprene technology could be reproduced in other market technologies. It should be noted that only four technologies of running shoes within multiple possibilities were evaluated, therefore, caution should be taken when transferring the present results to other technologies, even if they seem similar. A limitation of this study was that other structural elements of the running shoes, which could interfere with the perception of comfort, such as the types of sewing and the number of fabrics utilized in the design, were not evaluated. Additionally, because the running shoe’s size available was only 40, it was difficult to include women in the study. Our conclusions are also restricted to runners with rearfoot strike pattern. Future research involving the relationships between comfort and biomechanical variables should consider these design characteristics.
5. Conclusions The findings of the present study did not show significant associations between the biomechanical variables and the perception of comfort for three of the four different cushioning technologies (Gel, Air, and EVA with various densities). Only for the Adiprene technology running shoes, the general comfort and the perception of comfort were predicted by the loading rates over the forefoot. Thus, in general, it is not possible to predict general comfort of running shoes by means of received impacts and pressures.
6. Practical implications • High load rates have been associated with the risk of some injuries in recreational runners, however, the choice of running shoes should not be based solely upon perception of comfort, but upon the technology of the sole of the shoes, which provides lower loading rates. • None of the four cushioning technologies of the investigated running shoes resulted in substantial differences regarding the biomechanical variables. The technology which generated the lower impacts did not show any relationships with the perceived comfort. • Both the running shoes with the best and worse perception of comfort resulted in lower loading rates. All the investigated technologies demonstrated similar characteristics in reducing the impact during running.
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Acknowledgments The authors acknowledge the Brazilian Government Funding Agencies: State of Sao Paulo Research Foundation (FAPESP) and Coordination for the Improvement of Higher Level Personnel (CAPES). We attest that we do not have any conflict of interest with any footwear company. The shoes were purchased by the laboratory that performed the study. References 1. Tillman MD, Fiolkowski P, Bauer JA et al. In-shoe plantar measurements during running on different surfaces. Sports Eng 2002; 5:121–128. 2. Feehery RV. The biomechanics of running on different surfaces. Clin Podiatr Med Surg 1986; 3(4):649–659. 3. Novacheck TF. The biomechanics of running. Gait Posture 1998; 7(1):77–95. 4. Lieberman DE, Venkadesan M, Werbel WA et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 2010; 463(7280):531–535. 5. Pohl MB, Hamill J, Davis IS. Biomechanical and anatomic factors associated with a history of plantar fasciitis in female runners. Clin J Sport Med 2009; 19(5):372–376. 6. Crowell HP, Davis IS. Gait retraining to reduce lower extremity loading in runners. Clin Biomech (Bristol, Avon) 2011; 26(1):78–83. 7. Milner CE, Ferber R, Pollard CD et al. Biomechanical factors associated with tibial stress fracture in female runners. Med Sci Sports Exerc 2006; 38(2):323–328. 8. Radin EL, Yang KH, Riegger C et al. Relationship between lower limb dynamics and knee joint pain. J Orthop Res 1991; 9(3):398–405. 9. Bredeweg SW, Kluitenberg B, Bessem B et al. Differences in kinetic variables between injured and noninjured novice runners: A prospective cohort study. J Sci Med Sport 2012. 10. Verdejo R, Mills NJ. Heel-shoe interactions and the durability of EVA foam running-shoe midsoles. J Biomech 2004; 37(9):1379–1386. 11. Dixon SJ. Use of pressure insoles to compare in-shoe loading for modern running shoes. Ergonomics 2008; 51(10):1503–1514. 12. Hennig EM, Milani TL. Pressure distribution measurements for evaluation of running shoe properties. Sportverletz Sportschaden 2000; 14(3):90–97. 13. Clinghan R, Arnold GP, Drew TS et al. Do you get value for money when you buy an expensive pair of running shoes? Br J Sports Med 2008; 42(3):189–193. 14. Milani TL, Hennig EM, Lafortune MA. Perceptual and biomechanical variables for running in identical shoe constructions with varying midsole hardness. Clin Biomech (Bristol, Avon) 1997; 12(5):294–300. 15. Wegener C, Burns J, Penkala S. Effect of neutral-cushioned running shoes on plantar pressure loading and comfort in athletes with cavus feet: a crossover randomized controlled trial. Am J Sports Med 2008; 36(11):2139–2146. 16. Mündermann A, Stefanyshyn DJ, Nigg BM. Relationship between footwear comfort of shoe inserts and anthropometric and sensory factors. Med Sci Sports Exerc 2001; 33(11):1939–1945. 17. Hennig EM, Valiant GA, Liu Q. Biomechanical variables and the perception of cushioning for running in various types of footwear. J Appl Biomech 1996; 12(2):143–150. 18. Redmond AC, Crosbie J, Ouvrier RA. Development and validation of a novel rating system for scoring standing foot posture: the Foot Posture Index. Clin Biomech (Bristol Avon) 2006; 21(1):89–98. 19. Mündermann A, Nigg BM, Stefanyshyn DJ et al. Development of a reliable method to assess footwear comfort during running. Gait Posture 2002; 16(1):38–45. 20. Ribeiro AP, Trombini-Souza F, Tessutti VD et al. The effects of plantar fasciitis and pain on plantar pressure distribution of recreational runners. Clin Biomech (Bristol, Avon) 2011; 26(2):194–199. 21. Levin J, Fox JA, Brazil Estatística para ciências humanas, 2004. 22. Chen H, Nigg BM. Relationship between plantar pressure distribution under the foot and insole comfort. Clin Biomech 1994; 9:335–341. 23. Jordan C, Payton C, Bartlett R. Perceived comfort and pressure distribution in casual footwear. Clin Biomech (Bristol, Avon) 1997; 12(3):S5. 24. Nurse MA, Hulliger M, Wakeling JM et al. Changing the texture of footwear can alter gait patterns. J Electromyogr Kinesiol 2005; 15(5):496–506.
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