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The effect of foot type on in-shoe plantar pressure during walking and running
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Gait & Posture 28 (2008) 405–411 www.elsevier.com/locate/gaitpost
The effect of foot type on in-shoe plantar pressure during walking and running Bavornrit Chuckpaiwong a,b, James A. Nunley a, Nathan A. Mall b,c, Robin M. Queen a,b,* b
a Department of Surgery, Division of Orthopaedic Surgery, Duke University, Durham, NC, United States Michael W. Krzyzewski Human Performance Lab, Sports Medicine Program, Duke University, Durham, NC, United States c Department of Orthopaedic Surgery, Washington University, St. Louis, MO, United States
Received 21 February 2007; received in revised form 22 January 2008; accepted 24 January 2008
Abstract The purpose of this study was to determine if low arch feet have altered plantar loading patterns when compared to normal feet during both walking and running. Fifty healthy subjects (34 normal feet, 16 flat feet) walked and ran five trials each at standard speeds. In-shoe pressure data were collected at 50 Hz. Contact area, peak pressure, maximum force, and force-time integral were analyzed in eight different regions of the foot. Foot type was determined by examining navicular height, arch angle, rearfoot angle, and a clinical score. A series of 2 2 repeated measures ANOVAs were used to determine statistical differences (a < 0.05). A significant interaction existed between foot type and movement type for the maximum force in the medial midfoot. Total foot contact area, maximum force and peak pressure were significantly increased during running. Contact area in each insole area, except for the rearfoot, was significantly increased during running. Peak pressure and maximum force were significantly increased during running in each of the foot regions. However, the force-time integral was significantly decreased during running in the rearfoot, lateral midfoot, middle forefoot, and lateral forefoot. Significant differences between foot types existed for contact area in the medial midfoot and maximum force and peak pressure in the lateral forefoot. The maximum force and peak pressures were significantly decreased for the flat foot type. Therefore, individuals with a flat foot could be at a lower risk for lateral column metatarsal stress fractures, indicating that foot type should be assessed when determining an individual’s risk for metatarsal stress fractures. # 2008 Elsevier B.V. All rights reserved. Keywords: Plantar pressure; Foot type; Walking; Running; Running injuries
1. Introduction Many factors such as over training, low bone density, running on uneven surfaces, lower extremity malalignment as well as foot type have previously been associated with an increased risk of overuse injuries, specifically stress fractures [1]. In examining foot type, previous literature has indicated that individuals with a flat foot may be at increased risk for the development of many lower extremity overuse injuries including metatarsal stress fractures, iliotibial band syndrome, and * Corresponding author at: Michael W. Krzyzewski Human Performance Lab, 102 Finch Yeager Building, DUMC 3435, Duke University, Durham, NC 27710, United States. Tel.: +1 919 684 1853; fax: +1 919 681 7067. E-mail address: [email protected] (R.M. Queen). 0966-6362/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2008.01.012
patellofemoral pain syndrome [2]. A study by Simkin et al. focused on stress fracture injury risk as it is related to foot type and reported that individuals with a high arch were at increased risk for femoral and tibial stress fractures, while individuals with a low arch were at increased risk for the development of metatarsal stress fractures without specifying the location [3]. A study by Williams et al. focused specifically on stress fractures in runners and identified that runners with high arches were at increased risk for developing fifth metatarsal stress fractures, while runners with low arches were at increased risk for developing second and third metatarsal stress fractures [4]. Williams et al. stated that these differences in stress fracture injury risk were the result of altered lower extremity biomechanics in these two groups of individuals. The runners with low arches had an increase in
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rearfoot eversion velocity and eversion excursion [4]. In contrast, other authors have stated that no association exists between arch height and the risk for lower extremity injuries including stress fractures [2,5–7]. Substantial work has been done examining plantar pressure during walking both barefoot and in shoes as well as different speeds [8–13]. Increasing walking speed has been shown to result in increased plantar pressure in each of the foot regions that have been examined [8,12]. Walking speed has been shown to linearly influence the loading patterns beneath the hallux as well as the rearfoot [8,12–14], however, increases in walking speed had less of an effect on forefoot loading patterns [8]. Medial and middle forefoot loading initially increased at the slower walking speeds however remained constant or decreased as the subjects began to walk faster, which was attributed to a decrease in contact time as walking speed increased [8]. While changes in loading patterns were observed in the rearfoot, hallux and forefoot, the forces beneath the medial and lateral midfoot were not significantly altered with increased walking speed [12]. In addition to examining the influence of walking speed, previous literature has examined the effect of different footwear on plantar pressure patterns indicating that when subjects walked in running shoes the plantar pressure was significantly reduced when compared to barefoot walking [12,15]. In contrast to the information that is available examining plantar pressure distribution patterns during walking, very few studies have been completed that examine plantar pressure distribution patterns during running. Sneyers et al. examined the differences in plantar pressure patterns in pes planus, pes cavus, and normal foot types during barefoot running [16]. The results of this study indicated that the relative loads under the midfoot were decreased in the pes cavus foot type due to the lack of foot deformation that exists in the rigid pes cavus foot [16]. In addition, Sneyers et al. reported that in patients with a pes planus foot no significant medial shift existed in forefoot loading [16]. Sneyers et al. also demonstrated differences in loading patterns between running barefoot and in shoes indicating that more statistically significant differences existed between different foot types when examining the barefoot condition as compared to examining the shod running condition [16]. In addition to examining foot type in running, previous studies have examined the differences between running and walking at different speeds. Ground reaction forces rather than plantar loading patterns were analyzed [17,18]. However, one previous study by Burnfield et al. examined the differences in plantar loading at different walking speeds [12]. Their results indicated that with increased walking speed there was an increase in plantar loading [12]. To our knowledge, no current literature exists examining the differences in plantar pressure distribution patterns when comparing walking and running and when examining different foot types. Therefore, the purpose of this study was to investigate the differences in plantar pressure between walking and running and between subjects with
a normal and a low arch foot. We hypothesized that an increase in plantar pressure, maximum force and contact area would exist during running when compared to walking. In addition, the loading patterns would shift medially in the subjects with a low arch compared to a normal arch. 2. Materials and methods A total of 50 healthy active adults were recruited from the university and surrounding community. Demographic information for all subjects can be found in Table 1. All subjects were tested bilaterally; however, the right foot of each subject was used during statistical analysis. Inclusion criteria included a history of no lower extremity injuries within the past year and no history of foot and ankle surgery. All subjects read and signed an informed consent approved by the institutional review board. All subjects’ feet were marked at the following bony landmarks: the most plantar tip of the navicular tuberosity, 2 marks at the midline of the posterior calcaneal tuberosity, and 2 marks at the midline of Achilles tendon (Fig. 1). Patients were asked to stand with 90% of their weight on the mirrored foot photo box (MFPB) [19] which provided the visualization of medial, anterior, posterior and plantar views of the foot. In order to ensure that subjects were in 90% weight bearing they were asked to place one foot on the MFPB and the contralateral foot on a scale and to keep the weight on the scale to 10% of their body weight. All of the photographs were digitized and measured using the SigmaScan pro software (Systat Software Inc., Richmond, CA). Navicular height was defined as the distance between the floor and the lower border of navicular (navicular marker) in the medial view (Fig. 1A). Based on previous literature, a navicular height of less than 37 mm was considered to be abnormal [20]. Arch angle, obtained from the plantar view, was defined as the angle between the line connecting the most medial aspect of the heel to the most medial metatarsals, and the most lateral point of medial foot border to the most medial metatarsal (Fig. 2). An arch angle of less than 468 was considered abnormal [20]. The rearfoot angle was defined by the angle between mid calcaneal line and mid Achilles line from the posterior view (Fig. 1B). A rearfoot angle of more than 98 of valgus was considered abnormal [21,22]. All feet were examined and graded as flat or normal by a foot and ankle orthopaedic surgeon using the weight bearing alignment of the forefoot, midfoot and rearfoot in the coronal and sagittal planes as has been previously reported in the literature [11]. In order for the foot to be classified as flat, it had to be defined as flat in 3 of the 4 criteria (navicular height, arch angle, rearfoot angle, and a foot type given by a foot ankle orthopaedic surgeon). The pressures under the plantar surface of the foot were measured using the Pedar-X system (Novel, St. Paul, MN). The insoles were 2.5 mm thick and consisted of an array of 99 sensors that were evenly distributed over the insole with a spatial resolution of approximately 0.391 cm2/sensor. The insoles were sampled at 50 Hz for approximately 20 s. Table 1 Demographic data
Normal feet Flat feet p-Value
Age (years)
Height (m)
Weight (kg)
24.7 4.3 25.2 3.3 0.900
1.77 0.09 1.77 0.08 0.320
81.5 17.5 74.8 13.2 0.730
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Fig. 1. (A) Medial view of the foot and (B) posterior view of the foot.
All subjects were asked to walk over a 10 m walkway at a speed of 1.8 m/s 5% and to run over a 10 m walkway at 3.3 m/ s 5% while pressure beneath each foot was recorded. Running and walking speeds were monitored using two sets of infrared photocells positioned 6 m apart along the length of the walkway. The photocells were placed at approximately shoulder height to avoid being triggered by arm swing. Each subject completed five trials for both walking and running in their own running shoes. The following variables were analyzed for the entire foot: maximum force, peak pressure, and contact area. In addition, the foot was divided into the following eight anatomic regions: rearfoot, medial midfoot, lateral midfoot, medial forefoot, middle forefoot, lateral forefoot, hallux, and lesser toes (Fig. 3). The foot regions were defined as percentage masks within the software in order to make comparisons across the different size insoles. Within each of these foot regions, the following variables were analyzed during the stance phase of walking and running: contact area, peak pressure, maximum force, and the force-time integral. The stance phase for both tasks was defined as beginning when the first sensor displayed a pressure reading until pressure was no longer being recoded by the insoles. The maximum force was normalized to body weight for each subject and therefore is reported in units of body weight (BW) while the contact area was normalized to the contact area of the entire insole and therefore is reported in units of normalized insole contact area (NICA) [23]. The two foot types (flat and normal) and the two tasks (walking and running) were compared using a 2 2 repeated measures ANOVA with Tukey’s post hoc testing (a < 0.05) using SPSS version 12 (Chicago, IL).
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Fig. 2. Arch angle measurement defined as the angle (D) between the line connecting the most medial aspect of the heel to the most medial metatarsals (line AB), and the most lateral point of medial foot border to the most medial metatarsal (line AC).
3. Results Thirty-four feet (68%) were classified as having a normal arch, while 16 feet (32%) were classified as having a low arch. No significant differences in age ( p = 0.9), weight
Fig. 3. Significant main effects in plantar pressure patterns based on foot type. The arrows indicate a change in plantar pressure patterns when comparing flat feet to normal feet.
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Table 2 Plantar loading beneath the entire foot during both tasks
Normal feet Flat feet
Total foot contact area (NICA)+
Total foot peak pressure (kPa)+
Total foot maximum force (BW)+
Walking
Running
Walking
Running
Walking
Running
0.886 0.06 0.906 0.06
0.947 0.06 0.979 0.03
264.30 49.0 282.17 98.8
369.60 76.8 375.20 141.6
1.11 0.18 1.11 0.14
2.14 0.25 2.20 0.3
+
Significant main effect for movement (walking and running) ( p < 0.001).
various regions of the foot for most of the dependent variables. Contact area was significantly increased during running when compared to walking in the medial midfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p = 0.005), hallux ( p = 0.013), and the lesser toes ( p < 0.001) (Table 3). Maximum force normalized to body weight was significantly increased during running in the rearfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p < 0.001), hallux ( p < 0.001), and lesser toes ( p < 0.001) (Table 3). In addition, peak pressure was significantly greater during running in the rearfoot ( p < 0.001), medial midfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p < 0.001), hallux ( p < 0.001), and lesser toes ( p < 0.001) (Table 3). Finally, the force-time integral was significantly decreased during running in the rearfoot ( p < 0.001), lateral midfoot
( p = 0.32) or height ( p = 0.73) were found between the normal and low arch groups (Table 1). Only one significant interaction existed between movement type (walking and running) and foot type (normal and flat). The normalized maximum force in the medial midfoot was significantly increased in the low arch foot when compared to the normal foot during walking ( p = 0.001). No other significant interactions existed. No significant differences existed between the two foot types for total foot contact area, maximum force, or peak pressure (Table 2). However, a significant increase in contact area ( p < 0.001), maximum force ( p < 0.001) and peak pressure ( p < 0.001) existed during the running trials when compared with walking (Table 2). 3.1. Movement (walking vs. running) When the two movement tasks (walking and running) were compared, significant differences existed beneath the Table 3 Main effects for movement (walking vs. running) divided by foot region
Rearfoot Medial midfoot Lateral midfoot Medial forefoot Middle forefoot Lateral forefoot Hallux Lesser toes
Contact area (NICA)
Maximum force (BW)
Force-time integral (Ns)
Peak pressure (kPa)
Walking
Running
Walking
Running
Walking
Running
Walking
Running
0.249 0.011 0.090 0.039 0.147 0.012 0.073 0.006 0.085 0.005 0.082 0.005 0.063 0.004 0.105 0.012
0.238 0.039 0.139 0.025* 0.156 0.005* 0.077 0.002* 0.088 0.001* 0.084 0.001+ 0.064 0.003+ 0.110 0.007*
0.749 0.12 0.084 0.50 0.193 0.05 0.208 0.06 0.249 0.06 0.182 0.05 0.210 0.06 0.193 0.06
0.955 0.36* 0.250 0.10a 0.389 0.09* 0.346 0.10* 0.398 0.09* 0.296 0.08* 0.264 0.07* 0.277 0.07*
123.4 61.5 17.6 16.0 50.5 25.0 44.6 33.3 57.0 33.1 46.0 25.8 36.6 43.0 34.4 33.5
52.2 26.1* 18.8 11.6 35.7 16.0* 35.5 14.3 41.6 15.4* 31.3 13.3* 26.2 9.2 29.3 11.9
207.3 37.8 109.7 29.6 123.4 26.0 202.6 72.4 201.2 53.9 175.4 48.4 242.9 76.4 187.9 54.6
259.8 93.9* 159.8 39.1* 181.9 29.2* 304.6 118.6* 295.4 89.3* 246.2 71.6* 303.4 91.8* 260.0 86.7*
+
p < 0.05, *p < 0.01. a Interaction.
Table 4 Main effects for foot type (flat vs. normal) divided by foot region
Rearfoot Medial midfoot Lateral midfoot Medial forefoot Middle forefoot Lateral forefoot Hallux Lesser toes +
Contact area (NICA)
Maximum force (BW)
Force-time integral (Ns)
Peak pressure (kPa)
Normal arch
Low arch
Normal arch
Low arch
Normal arch
Low arch
Normal arch
Low arch
0.242 0.004 0.108 0.005 0.152 0.001 0.075 0.001 0.087 0.001 0.083 0.001 0.064 0.001 0.106 0.001
0.248 0.005 0.130 0.007* 0.152 0.002 0.075 0.001 0.086 0.001 0.082 0.001 0.064 0.001 0.110 0.002
0.836 0.04 0.143 0.01 0.281 0.01 0.278 0.01 0.333 0.01 0.250 0.01 0.231 0.01 0.228 0.01
0.886 0.06 0.218 0.15a 0.312 0.02 0.274 0.02 0.303 0.02 0.215 0.01+ 0.250 0.02 0.249 0.02
89.4 6.5 16.3 2.1 41.9 3.1 42.4 3.7 52.9 3.7 41.6 3.0 33.3 4.2 33.2 3.6
84.5 9.4 22.2 3.0 45.7 4.5 35.0 5.4 41.6 5.4 32.2 4.4 27.3 6.1 28.9 5.2
230.5 9.9 134.4 5.3 154.9 4.9 253.0 15.9 255.0 11.7 221.5 9.6 269.4 13.2 223.3 11.7
239.9 14.4 135.4 7.8 147.8 7.2 254.9 23.2 234.1 17.1 188.0 14.0+ 281.1 19.2 225.4 17.0
p < 0.05, *p < 0.01. a Interaction.
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( p < 0.001), middle forefoot ( p = 0.001), and the lateral forefoot ( p < 0.001) (Table 3). 3.2. Foot type (flat vs. normal) No significant differences existed between foot type (normal vs. low arch) for the force-time integral (Table 4). However, the contact area beneath the medial midfoot was significantly increased in the low arch foot when compared to the normal foot ( p = 0.008). In addition, the maximum force beneath the lateral forefoot was significantly increased in the normal foot when compared to the low arch foot ( p = 0.04) (Table 4). A significant decrease in peak pressure beneath the lateral forefoot also existed for the low arch feet when compared with the normal feet ( p = 0.05). No other significant main effects for foot type existed for any of the study variables in any of the foot regions (Fig. 3).
4. Discussion The results of this study indicate that during running the contact area, maximum force, and peak pressure were significantly increased when compared to walking. The only foot region that did not show an increase in contact area during running was the rearfoot. The decrease in contact area in the rearfoot during running was not statistically significant; however, it could be the result of different foot strike patterns during running. Previous research has examined the influence of foot strike patterns on ground reaction forces determining that significant differences in loading characteristics exist between rearfoot, midfoot and forefoot strikers [16,17]. The change from a rearfoot strike pattern during walking to more of a midfoot strike pattern during running could explain the decrease in contact area in the rearfoot during running. The increase in peak pressure and maximum force during running is consistent with the current literature that has examined the effect of walking speed on plantar pressure patterns in which these parameters were shown to be increased with increased walking speed [8,12,13]. Previous research that has examined changes in the vertical ground reaction forces between walking and running has identified an increase in peak force from approximately 1.0 BW to between 2.0 and 2.9B W depending on the running speed [17,18]. Similarly, this study demonstrated a total foot maximum force increase from 1.11 to 2.14 BW when comparing walking and running. The only significant difference between foot types were the contact area and maximum force in the medial midfoot as well as the maximum force and peak pressure in the lateral forefoot. The contact area and maximum force in the medial midfoot were significantly greater for the low arch foot, while the peak pressure and maximum force in the lateral forefoot were significantly decreased in the low arch foot when compared to the normal foot. The results of the
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current study are similar to the results of a study by Sneyers et al. that demonstrated no significant medial shift in the loading patterns in the rearfoot in individuals with a flat foot when compared to individuals with a cavus foot type [16]. However, the results of this study indicate a difference in loading in the forefoot, with a significant decrease in load in lateral forefoot in individuals with a flat foot, which is in contrast to the results presented by Sneyers et al. that indicated no significant medial shift in forefoot loading [16]. The differences between the results of this study and those of Sneyers et al. could be a difference in the testing conditions. In the current study, subjects were tested in running shoes, whereas Sneyers et al. completed all testing barefoot [16]. With subjects being tested in their own running shoe the medial load shift could be affected by the presence or absence of a shoe with a dual density midsole. This type of running shoe is designed to decrease pronation and therefore could potentially influence the loading on the medial portion of the foot during running especially in subjects with a flat foot. Previous literature has examined the influence of foot type on the incidence of overuse injuries, specifically stress fractures [2–6]. The current literature is unclear as to whether having a flat foot is advantageous in preventing metatarsal stress fractures or increases the risk of a stress fracture. Therefore, this study examined the differences in loading patterns between individuals with a normal arch height and those with low arches in order to determine the differences in loading patterns and how these differences could be related to potential injury risk factors. The decrease in peak pressure and maximum force in the lateral forefoot in the individuals with a flat foot could indicate that they might have a decreased risk of developing fifth metatarsal stress fractures when compared to individuals with a normal arch height. One previous study by Williams et al. identified that runners with high arches were at increased risk for the development of fifth metatarsal stress fractures [4]. While previous literature has indicated that individuals with a low arch might be at increased risk for second and third metatarsal stress fractures [4], the current study does not demonstrate an increase in loading in the medial or middle forefoot that could be associated with the potential for increased injury risk. No absolute load threshold has been identified that predisposes an individual to overuse injuries. In addition, many factors are involved in the development of overuse injuries including the amount of load, the loading rate, an abrupt increase in activity, and bone quality. Future studies should focus on the effect of foot type on various types of dynamic athletic tasks such as cutting and jumping in order to determine whether foot type alters plantar loading during more dynamic tasks. While plantar pressure and plantar loading are useful tools to investigate biomechanical factors influencing foot and ankle pathology, it is important to consider the limitations of such data [8,9,24,25]. Comparison of plantar loading across studies should be carefully considered as
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various factors such as the instrumentation used (type and size of transducer), the sampling rate, the shoes that are used for testing, and the movement speed can all influence the pressure measurements [10,11,19]. In the current study, the variations within the subject sample were minimized by including only young adult subjects with no history of foot and ankle injury or pain. One possible limitation to the current study was the use of each subject’s own footwear for testing. While bench testing has demonstrated that deceleration forces increase with greater midsole stiffness, this trend is often not present during running trials for which GRF data are recorded [26,27]. The results of previous running studies have suggested that midsole density may have no significant effect on the magnitude of the vertical GRF at impact [28–31]. The non-significant difference in the GRF measurements could be the result of kinematic adaptations by runners in an attempt to increase the deceleration time in a shoe with a harder midsole. Therefore, in future studies subjects should potentially be tested in the same type of footwear in order to determine how plantar loading is affected by changes in midsole density as compared to the results that exist with respect to ground reaction forces. Additionally, when comparing studies it is important to consider how foot type was defined. In previous studies, foot type or the height of the longitudinal arch of foot has been defined by many techniques including clinical examination and foot print measurement, however, a gold standard has still not been established [11,19,20,32–34]. Many studies have defined foot type by only a single parameter [4,11,35], however, the current study attempted to avoid these issues by using both a clinical evaluation and several different anatomically measured foot parameters that have been previously validated [20,33,34]. Previous literature has indicated that specific athletic movements influence plantar loading [24,36]. However, these differences in plantar loading were not assessed based on the foot type of the individuals completing the different tasks. While the current study has identified that individuals with low arches may be at decreased risk for the development of fifth metatarsal stress fractures, future work should focus on the effect of foot type on plantar loading during different athletic tasks. Work by Queen et al. [36] has indicated that when completing different soccer specific tasks such as a cross-over cut that an increase in maximum force existed in the lateral forefoot when compared to other tasks such as a side cut and forward acceleration. Therefore, examining these types of sport specific tasks in individuals with different foot types may aid in the understanding of potential risk factors for injury and could lead to alterations in orthotic or shoe design to aid in the prevention of over use injuries, particularly metatarsal stress fractures. Conflict of interest None.
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Gait & Posture 28 (2008) 405–411 www.elsevier.com/locate/gaitpost
The effect of foot type on in-shoe plantar pressure during walking and running Bavornrit Chuckpaiwong a,b, James A. Nunley a, Nathan A. Mall b,c, Robin M. Queen a,b,* b
a Department of Surgery, Division of Orthopaedic Surgery, Duke University, Durham, NC, United States Michael W. Krzyzewski Human Performance Lab, Sports Medicine Program, Duke University, Durham, NC, United States c Department of Orthopaedic Surgery, Washington University, St. Louis, MO, United States
Received 21 February 2007; received in revised form 22 January 2008; accepted 24 January 2008
Abstract The purpose of this study was to determine if low arch feet have altered plantar loading patterns when compared to normal feet during both walking and running. Fifty healthy subjects (34 normal feet, 16 flat feet) walked and ran five trials each at standard speeds. In-shoe pressure data were collected at 50 Hz. Contact area, peak pressure, maximum force, and force-time integral were analyzed in eight different regions of the foot. Foot type was determined by examining navicular height, arch angle, rearfoot angle, and a clinical score. A series of 2 2 repeated measures ANOVAs were used to determine statistical differences (a < 0.05). A significant interaction existed between foot type and movement type for the maximum force in the medial midfoot. Total foot contact area, maximum force and peak pressure were significantly increased during running. Contact area in each insole area, except for the rearfoot, was significantly increased during running. Peak pressure and maximum force were significantly increased during running in each of the foot regions. However, the force-time integral was significantly decreased during running in the rearfoot, lateral midfoot, middle forefoot, and lateral forefoot. Significant differences between foot types existed for contact area in the medial midfoot and maximum force and peak pressure in the lateral forefoot. The maximum force and peak pressures were significantly decreased for the flat foot type. Therefore, individuals with a flat foot could be at a lower risk for lateral column metatarsal stress fractures, indicating that foot type should be assessed when determining an individual’s risk for metatarsal stress fractures. # 2008 Elsevier B.V. All rights reserved. Keywords: Plantar pressure; Foot type; Walking; Running; Running injuries
1. Introduction Many factors such as over training, low bone density, running on uneven surfaces, lower extremity malalignment as well as foot type have previously been associated with an increased risk of overuse injuries, specifically stress fractures [1]. In examining foot type, previous literature has indicated that individuals with a flat foot may be at increased risk for the development of many lower extremity overuse injuries including metatarsal stress fractures, iliotibial band syndrome, and * Corresponding author at: Michael W. Krzyzewski Human Performance Lab, 102 Finch Yeager Building, DUMC 3435, Duke University, Durham, NC 27710, United States. Tel.: +1 919 684 1853; fax: +1 919 681 7067. E-mail address: [email protected] (R.M. Queen). 0966-6362/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2008.01.012
patellofemoral pain syndrome [2]. A study by Simkin et al. focused on stress fracture injury risk as it is related to foot type and reported that individuals with a high arch were at increased risk for femoral and tibial stress fractures, while individuals with a low arch were at increased risk for the development of metatarsal stress fractures without specifying the location [3]. A study by Williams et al. focused specifically on stress fractures in runners and identified that runners with high arches were at increased risk for developing fifth metatarsal stress fractures, while runners with low arches were at increased risk for developing second and third metatarsal stress fractures [4]. Williams et al. stated that these differences in stress fracture injury risk were the result of altered lower extremity biomechanics in these two groups of individuals. The runners with low arches had an increase in
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rearfoot eversion velocity and eversion excursion [4]. In contrast, other authors have stated that no association exists between arch height and the risk for lower extremity injuries including stress fractures [2,5–7]. Substantial work has been done examining plantar pressure during walking both barefoot and in shoes as well as different speeds [8–13]. Increasing walking speed has been shown to result in increased plantar pressure in each of the foot regions that have been examined [8,12]. Walking speed has been shown to linearly influence the loading patterns beneath the hallux as well as the rearfoot [8,12–14], however, increases in walking speed had less of an effect on forefoot loading patterns [8]. Medial and middle forefoot loading initially increased at the slower walking speeds however remained constant or decreased as the subjects began to walk faster, which was attributed to a decrease in contact time as walking speed increased [8]. While changes in loading patterns were observed in the rearfoot, hallux and forefoot, the forces beneath the medial and lateral midfoot were not significantly altered with increased walking speed [12]. In addition to examining the influence of walking speed, previous literature has examined the effect of different footwear on plantar pressure patterns indicating that when subjects walked in running shoes the plantar pressure was significantly reduced when compared to barefoot walking [12,15]. In contrast to the information that is available examining plantar pressure distribution patterns during walking, very few studies have been completed that examine plantar pressure distribution patterns during running. Sneyers et al. examined the differences in plantar pressure patterns in pes planus, pes cavus, and normal foot types during barefoot running [16]. The results of this study indicated that the relative loads under the midfoot were decreased in the pes cavus foot type due to the lack of foot deformation that exists in the rigid pes cavus foot [16]. In addition, Sneyers et al. reported that in patients with a pes planus foot no significant medial shift existed in forefoot loading [16]. Sneyers et al. also demonstrated differences in loading patterns between running barefoot and in shoes indicating that more statistically significant differences existed between different foot types when examining the barefoot condition as compared to examining the shod running condition [16]. In addition to examining foot type in running, previous studies have examined the differences between running and walking at different speeds. Ground reaction forces rather than plantar loading patterns were analyzed [17,18]. However, one previous study by Burnfield et al. examined the differences in plantar loading at different walking speeds [12]. Their results indicated that with increased walking speed there was an increase in plantar loading [12]. To our knowledge, no current literature exists examining the differences in plantar pressure distribution patterns when comparing walking and running and when examining different foot types. Therefore, the purpose of this study was to investigate the differences in plantar pressure between walking and running and between subjects with
a normal and a low arch foot. We hypothesized that an increase in plantar pressure, maximum force and contact area would exist during running when compared to walking. In addition, the loading patterns would shift medially in the subjects with a low arch compared to a normal arch. 2. Materials and methods A total of 50 healthy active adults were recruited from the university and surrounding community. Demographic information for all subjects can be found in Table 1. All subjects were tested bilaterally; however, the right foot of each subject was used during statistical analysis. Inclusion criteria included a history of no lower extremity injuries within the past year and no history of foot and ankle surgery. All subjects read and signed an informed consent approved by the institutional review board. All subjects’ feet were marked at the following bony landmarks: the most plantar tip of the navicular tuberosity, 2 marks at the midline of the posterior calcaneal tuberosity, and 2 marks at the midline of Achilles tendon (Fig. 1). Patients were asked to stand with 90% of their weight on the mirrored foot photo box (MFPB) [19] which provided the visualization of medial, anterior, posterior and plantar views of the foot. In order to ensure that subjects were in 90% weight bearing they were asked to place one foot on the MFPB and the contralateral foot on a scale and to keep the weight on the scale to 10% of their body weight. All of the photographs were digitized and measured using the SigmaScan pro software (Systat Software Inc., Richmond, CA). Navicular height was defined as the distance between the floor and the lower border of navicular (navicular marker) in the medial view (Fig. 1A). Based on previous literature, a navicular height of less than 37 mm was considered to be abnormal [20]. Arch angle, obtained from the plantar view, was defined as the angle between the line connecting the most medial aspect of the heel to the most medial metatarsals, and the most lateral point of medial foot border to the most medial metatarsal (Fig. 2). An arch angle of less than 468 was considered abnormal [20]. The rearfoot angle was defined by the angle between mid calcaneal line and mid Achilles line from the posterior view (Fig. 1B). A rearfoot angle of more than 98 of valgus was considered abnormal [21,22]. All feet were examined and graded as flat or normal by a foot and ankle orthopaedic surgeon using the weight bearing alignment of the forefoot, midfoot and rearfoot in the coronal and sagittal planes as has been previously reported in the literature [11]. In order for the foot to be classified as flat, it had to be defined as flat in 3 of the 4 criteria (navicular height, arch angle, rearfoot angle, and a foot type given by a foot ankle orthopaedic surgeon). The pressures under the plantar surface of the foot were measured using the Pedar-X system (Novel, St. Paul, MN). The insoles were 2.5 mm thick and consisted of an array of 99 sensors that were evenly distributed over the insole with a spatial resolution of approximately 0.391 cm2/sensor. The insoles were sampled at 50 Hz for approximately 20 s. Table 1 Demographic data
Normal feet Flat feet p-Value
Age (years)
Height (m)
Weight (kg)
24.7 4.3 25.2 3.3 0.900
1.77 0.09 1.77 0.08 0.320
81.5 17.5 74.8 13.2 0.730
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Fig. 1. (A) Medial view of the foot and (B) posterior view of the foot.
All subjects were asked to walk over a 10 m walkway at a speed of 1.8 m/s 5% and to run over a 10 m walkway at 3.3 m/ s 5% while pressure beneath each foot was recorded. Running and walking speeds were monitored using two sets of infrared photocells positioned 6 m apart along the length of the walkway. The photocells were placed at approximately shoulder height to avoid being triggered by arm swing. Each subject completed five trials for both walking and running in their own running shoes. The following variables were analyzed for the entire foot: maximum force, peak pressure, and contact area. In addition, the foot was divided into the following eight anatomic regions: rearfoot, medial midfoot, lateral midfoot, medial forefoot, middle forefoot, lateral forefoot, hallux, and lesser toes (Fig. 3). The foot regions were defined as percentage masks within the software in order to make comparisons across the different size insoles. Within each of these foot regions, the following variables were analyzed during the stance phase of walking and running: contact area, peak pressure, maximum force, and the force-time integral. The stance phase for both tasks was defined as beginning when the first sensor displayed a pressure reading until pressure was no longer being recoded by the insoles. The maximum force was normalized to body weight for each subject and therefore is reported in units of body weight (BW) while the contact area was normalized to the contact area of the entire insole and therefore is reported in units of normalized insole contact area (NICA) [23]. The two foot types (flat and normal) and the two tasks (walking and running) were compared using a 2 2 repeated measures ANOVA with Tukey’s post hoc testing (a < 0.05) using SPSS version 12 (Chicago, IL).
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Fig. 2. Arch angle measurement defined as the angle (D) between the line connecting the most medial aspect of the heel to the most medial metatarsals (line AB), and the most lateral point of medial foot border to the most medial metatarsal (line AC).
3. Results Thirty-four feet (68%) were classified as having a normal arch, while 16 feet (32%) were classified as having a low arch. No significant differences in age ( p = 0.9), weight
Fig. 3. Significant main effects in plantar pressure patterns based on foot type. The arrows indicate a change in plantar pressure patterns when comparing flat feet to normal feet.
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Table 2 Plantar loading beneath the entire foot during both tasks
Normal feet Flat feet
Total foot contact area (NICA)+
Total foot peak pressure (kPa)+
Total foot maximum force (BW)+
Walking
Running
Walking
Running
Walking
Running
0.886 0.06 0.906 0.06
0.947 0.06 0.979 0.03
264.30 49.0 282.17 98.8
369.60 76.8 375.20 141.6
1.11 0.18 1.11 0.14
2.14 0.25 2.20 0.3
+
Significant main effect for movement (walking and running) ( p < 0.001).
various regions of the foot for most of the dependent variables. Contact area was significantly increased during running when compared to walking in the medial midfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p = 0.005), hallux ( p = 0.013), and the lesser toes ( p < 0.001) (Table 3). Maximum force normalized to body weight was significantly increased during running in the rearfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p < 0.001), hallux ( p < 0.001), and lesser toes ( p < 0.001) (Table 3). In addition, peak pressure was significantly greater during running in the rearfoot ( p < 0.001), medial midfoot ( p < 0.001), lateral midfoot ( p < 0.001), medial forefoot ( p < 0.001), middle forefoot ( p < 0.001), lateral forefoot ( p < 0.001), hallux ( p < 0.001), and lesser toes ( p < 0.001) (Table 3). Finally, the force-time integral was significantly decreased during running in the rearfoot ( p < 0.001), lateral midfoot
( p = 0.32) or height ( p = 0.73) were found between the normal and low arch groups (Table 1). Only one significant interaction existed between movement type (walking and running) and foot type (normal and flat). The normalized maximum force in the medial midfoot was significantly increased in the low arch foot when compared to the normal foot during walking ( p = 0.001). No other significant interactions existed. No significant differences existed between the two foot types for total foot contact area, maximum force, or peak pressure (Table 2). However, a significant increase in contact area ( p < 0.001), maximum force ( p < 0.001) and peak pressure ( p < 0.001) existed during the running trials when compared with walking (Table 2). 3.1. Movement (walking vs. running) When the two movement tasks (walking and running) were compared, significant differences existed beneath the Table 3 Main effects for movement (walking vs. running) divided by foot region
Rearfoot Medial midfoot Lateral midfoot Medial forefoot Middle forefoot Lateral forefoot Hallux Lesser toes
Contact area (NICA)
Maximum force (BW)
Force-time integral (Ns)
Peak pressure (kPa)
Walking
Running
Walking
Running
Walking
Running
Walking
Running
0.249 0.011 0.090 0.039 0.147 0.012 0.073 0.006 0.085 0.005 0.082 0.005 0.063 0.004 0.105 0.012
0.238 0.039 0.139 0.025* 0.156 0.005* 0.077 0.002* 0.088 0.001* 0.084 0.001+ 0.064 0.003+ 0.110 0.007*
0.749 0.12 0.084 0.50 0.193 0.05 0.208 0.06 0.249 0.06 0.182 0.05 0.210 0.06 0.193 0.06
0.955 0.36* 0.250 0.10a 0.389 0.09* 0.346 0.10* 0.398 0.09* 0.296 0.08* 0.264 0.07* 0.277 0.07*
123.4 61.5 17.6 16.0 50.5 25.0 44.6 33.3 57.0 33.1 46.0 25.8 36.6 43.0 34.4 33.5
52.2 26.1* 18.8 11.6 35.7 16.0* 35.5 14.3 41.6 15.4* 31.3 13.3* 26.2 9.2 29.3 11.9
207.3 37.8 109.7 29.6 123.4 26.0 202.6 72.4 201.2 53.9 175.4 48.4 242.9 76.4 187.9 54.6
259.8 93.9* 159.8 39.1* 181.9 29.2* 304.6 118.6* 295.4 89.3* 246.2 71.6* 303.4 91.8* 260.0 86.7*
+
p < 0.05, *p < 0.01. a Interaction.
Table 4 Main effects for foot type (flat vs. normal) divided by foot region
Rearfoot Medial midfoot Lateral midfoot Medial forefoot Middle forefoot Lateral forefoot Hallux Lesser toes +
Contact area (NICA)
Maximum force (BW)
Force-time integral (Ns)
Peak pressure (kPa)
Normal arch
Low arch
Normal arch
Low arch
Normal arch
Low arch
Normal arch
Low arch
0.242 0.004 0.108 0.005 0.152 0.001 0.075 0.001 0.087 0.001 0.083 0.001 0.064 0.001 0.106 0.001
0.248 0.005 0.130 0.007* 0.152 0.002 0.075 0.001 0.086 0.001 0.082 0.001 0.064 0.001 0.110 0.002
0.836 0.04 0.143 0.01 0.281 0.01 0.278 0.01 0.333 0.01 0.250 0.01 0.231 0.01 0.228 0.01
0.886 0.06 0.218 0.15a 0.312 0.02 0.274 0.02 0.303 0.02 0.215 0.01+ 0.250 0.02 0.249 0.02
89.4 6.5 16.3 2.1 41.9 3.1 42.4 3.7 52.9 3.7 41.6 3.0 33.3 4.2 33.2 3.6
84.5 9.4 22.2 3.0 45.7 4.5 35.0 5.4 41.6 5.4 32.2 4.4 27.3 6.1 28.9 5.2
230.5 9.9 134.4 5.3 154.9 4.9 253.0 15.9 255.0 11.7 221.5 9.6 269.4 13.2 223.3 11.7
239.9 14.4 135.4 7.8 147.8 7.2 254.9 23.2 234.1 17.1 188.0 14.0+ 281.1 19.2 225.4 17.0
p < 0.05, *p < 0.01. a Interaction.
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( p < 0.001), middle forefoot ( p = 0.001), and the lateral forefoot ( p < 0.001) (Table 3). 3.2. Foot type (flat vs. normal) No significant differences existed between foot type (normal vs. low arch) for the force-time integral (Table 4). However, the contact area beneath the medial midfoot was significantly increased in the low arch foot when compared to the normal foot ( p = 0.008). In addition, the maximum force beneath the lateral forefoot was significantly increased in the normal foot when compared to the low arch foot ( p = 0.04) (Table 4). A significant decrease in peak pressure beneath the lateral forefoot also existed for the low arch feet when compared with the normal feet ( p = 0.05). No other significant main effects for foot type existed for any of the study variables in any of the foot regions (Fig. 3).
4. Discussion The results of this study indicate that during running the contact area, maximum force, and peak pressure were significantly increased when compared to walking. The only foot region that did not show an increase in contact area during running was the rearfoot. The decrease in contact area in the rearfoot during running was not statistically significant; however, it could be the result of different foot strike patterns during running. Previous research has examined the influence of foot strike patterns on ground reaction forces determining that significant differences in loading characteristics exist between rearfoot, midfoot and forefoot strikers [16,17]. The change from a rearfoot strike pattern during walking to more of a midfoot strike pattern during running could explain the decrease in contact area in the rearfoot during running. The increase in peak pressure and maximum force during running is consistent with the current literature that has examined the effect of walking speed on plantar pressure patterns in which these parameters were shown to be increased with increased walking speed [8,12,13]. Previous research that has examined changes in the vertical ground reaction forces between walking and running has identified an increase in peak force from approximately 1.0 BW to between 2.0 and 2.9B W depending on the running speed [17,18]. Similarly, this study demonstrated a total foot maximum force increase from 1.11 to 2.14 BW when comparing walking and running. The only significant difference between foot types were the contact area and maximum force in the medial midfoot as well as the maximum force and peak pressure in the lateral forefoot. The contact area and maximum force in the medial midfoot were significantly greater for the low arch foot, while the peak pressure and maximum force in the lateral forefoot were significantly decreased in the low arch foot when compared to the normal foot. The results of the
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current study are similar to the results of a study by Sneyers et al. that demonstrated no significant medial shift in the loading patterns in the rearfoot in individuals with a flat foot when compared to individuals with a cavus foot type [16]. However, the results of this study indicate a difference in loading in the forefoot, with a significant decrease in load in lateral forefoot in individuals with a flat foot, which is in contrast to the results presented by Sneyers et al. that indicated no significant medial shift in forefoot loading [16]. The differences between the results of this study and those of Sneyers et al. could be a difference in the testing conditions. In the current study, subjects were tested in running shoes, whereas Sneyers et al. completed all testing barefoot [16]. With subjects being tested in their own running shoe the medial load shift could be affected by the presence or absence of a shoe with a dual density midsole. This type of running shoe is designed to decrease pronation and therefore could potentially influence the loading on the medial portion of the foot during running especially in subjects with a flat foot. Previous literature has examined the influence of foot type on the incidence of overuse injuries, specifically stress fractures [2–6]. The current literature is unclear as to whether having a flat foot is advantageous in preventing metatarsal stress fractures or increases the risk of a stress fracture. Therefore, this study examined the differences in loading patterns between individuals with a normal arch height and those with low arches in order to determine the differences in loading patterns and how these differences could be related to potential injury risk factors. The decrease in peak pressure and maximum force in the lateral forefoot in the individuals with a flat foot could indicate that they might have a decreased risk of developing fifth metatarsal stress fractures when compared to individuals with a normal arch height. One previous study by Williams et al. identified that runners with high arches were at increased risk for the development of fifth metatarsal stress fractures [4]. While previous literature has indicated that individuals with a low arch might be at increased risk for second and third metatarsal stress fractures [4], the current study does not demonstrate an increase in loading in the medial or middle forefoot that could be associated with the potential for increased injury risk. No absolute load threshold has been identified that predisposes an individual to overuse injuries. In addition, many factors are involved in the development of overuse injuries including the amount of load, the loading rate, an abrupt increase in activity, and bone quality. Future studies should focus on the effect of foot type on various types of dynamic athletic tasks such as cutting and jumping in order to determine whether foot type alters plantar loading during more dynamic tasks. While plantar pressure and plantar loading are useful tools to investigate biomechanical factors influencing foot and ankle pathology, it is important to consider the limitations of such data [8,9,24,25]. Comparison of plantar loading across studies should be carefully considered as
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various factors such as the instrumentation used (type and size of transducer), the sampling rate, the shoes that are used for testing, and the movement speed can all influence the pressure measurements [10,11,19]. In the current study, the variations within the subject sample were minimized by including only young adult subjects with no history of foot and ankle injury or pain. One possible limitation to the current study was the use of each subject’s own footwear for testing. While bench testing has demonstrated that deceleration forces increase with greater midsole stiffness, this trend is often not present during running trials for which GRF data are recorded [26,27]. The results of previous running studies have suggested that midsole density may have no significant effect on the magnitude of the vertical GRF at impact [28–31]. The non-significant difference in the GRF measurements could be the result of kinematic adaptations by runners in an attempt to increase the deceleration time in a shoe with a harder midsole. Therefore, in future studies subjects should potentially be tested in the same type of footwear in order to determine how plantar loading is affected by changes in midsole density as compared to the results that exist with respect to ground reaction forces. Additionally, when comparing studies it is important to consider how foot type was defined. In previous studies, foot type or the height of the longitudinal arch of foot has been defined by many techniques including clinical examination and foot print measurement, however, a gold standard has still not been established [11,19,20,32–34]. Many studies have defined foot type by only a single parameter [4,11,35], however, the current study attempted to avoid these issues by using both a clinical evaluation and several different anatomically measured foot parameters that have been previously validated [20,33,34]. Previous literature has indicated that specific athletic movements influence plantar loading [24,36]. However, these differences in plantar loading were not assessed based on the foot type of the individuals completing the different tasks. While the current study has identified that individuals with low arches may be at decreased risk for the development of fifth metatarsal stress fractures, future work should focus on the effect of foot type on plantar loading during different athletic tasks. Work by Queen et al. [36] has indicated that when completing different soccer specific tasks such as a cross-over cut that an increase in maximum force existed in the lateral forefoot when compared to other tasks such as a side cut and forward acceleration. Therefore, examining these types of sport specific tasks in individuals with different foot types may aid in the understanding of potential risk factors for injury and could lead to alterations in orthotic or shoe design to aid in the prevention of over use injuries, particularly metatarsal stress fractures. Conflict of interest None.
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