Understanding the role of foot biomechanics on regional foot orthosis deformation in flatfoot individuals during walking

BackgroundFoot orthoses (FOs) are one of the most common interventions to restore normal foot mechanics in flatfoot individuals. New technologies have made it possible to deliver customized FOs with complex designs for potentially better functionalities. However, translating the individuals’ biomechanical needs into the design of customized FOs is not yet fully understood.Research questionOur objective was to identify whether the deformation of customized FOs is related to foot kinematics and plantar pressure during walking.MethodsThe kinematics of multi-segment foot and FOs contour were recorded together with plantar pressure in 17 flatfoot individuals while walking with customized FOs. The deformation of FOs surface was predicted from its contour kinematics using an artificial neural network. Plantar pressure map and deformation were divided into five anatomically based regions defined by the corresponding foot segments. Forward stepwise linear mixed models were built for each of the four gait phases to determine the feet-FOs interaction.ResultsIt was observed that some associations existed between foot kinematics and pressure with regional FOs deformation. From heel-strike to foot-flat, longitudinal arch angle was associated with FOs deformation in forefoot. From foot-flat to midstance, rearfoot eversion accounted for variation in the deformation of medial FOs regions, and forefoot abduction for the lateral regions. From midstance to heel-off, rearfoot eversion, longitudinal arch angle, and plantar pressure played significant role in deformation. Finally, from heel-off to toe-off, forefoot adduction affected the deformation of forefoot and midfoot.SignificanceThis study provides guidelines for designing customized FOs. Flatfoot individuals with excessive rearfoot eversion or very flexible medial arches require more support on medial FOs regions, while the ones with excessive forefoot abduction need the support on lateral regions. However, a compromise should be made between the level of support and the level of increase in plantar pressure to avoid stress on foot structures.     

Subtalar neutral position as an offset for a kinematic model of the foot during walking

The lack of a common reference position when defining foot postures may underestimate the ability to differentiate foot function in subjects with pathology. The effect of using the subtalar neutral (STN) position as an offset for both rearfoot and forefoot through comparison of the kinematic walking patterns of subjects classified as normal (n=7) and abnormally pronated (n=14) foot postures was completed. An Optotrak Motion Analysis System (Northern Digital, Inc.) integrated with Motion Monitor Software (Innovative Sports, Inc.) was used to track three-dimensional movement of the leg, rearfoot and first metatarsal segments. Intrarater reliability of positioning the foot into STN using clinical guidelines was determined for a single rater for 21 subjects. Walking data were subsequently compared before and after an offset was applied to the rearfoot and first metatarsal segments. Repeated measures of foot positioning found the STN position to be highly repeatable (intraclass correlation coefficients>0.9), with peak errors ranging from 1.9 degrees to 4.3 degrees . Utilizing STN as the offset resulted in a significant increase in rearfoot eversion (p=0.019) during early stance, and greater first metatarsal dorsiflexion (p<0.007) across stance in the pronated foot groups that was not observed prior to applying the offset. When applied to subjects with differing foot postures, the selection of a common reference position that is both clinically appropriate and reliable may distinguish kinematic patterns during walking that are consistent with theories of abnormal pronation.     

A comparison of gait initiation and termination methods for obtaining plantar foot pressures

The midgait protocol is the most commonly used method to collect pressure platform data. Spatial limitations, however, frequently render this technique unsuitable. Alternative gait protocols have focused on gait initiation procedures in obtaining data. The current study investigated whether a commonly cited two-step gait initiation protocol, or a two-step gait termination protocol produced pressure data more representative of the criterion, midgait method. A pressure platform was used to collect data for 25 asymptomatic subjects using the midgait, two-step gait initiation and two-step gait termination walking protocols. The contact duration, percentage contact duration, peak pressure, peak force, pressure–time integral and force–time integral were calculated for seven sites within the foot. Multivariate analysis of variance with repeated measures identified significant protocol by site interactions for all variables except the force-time integral. The gait initiation protocol, although having minimal effect on peak pressures beneath the forefoot, markedly altered the relative timing parameters of the foot. In contrast, the gait termination protocol had minimal effect on temporal parameters, but resulted in a reduction in pressures beneath the forefoot. Abbreviated gait protocols are often employed in plantar pressure studies. This study suggests that the choice between a gait initiation and termination protocol is largely dependent on the gait parameter of interest.     

Effects of experimentally induced plantar insensitivity on forces and pressures under the foot during normal walking

Pressures under the foot during level walking were measured in 15 healthy young adults (8 females, 7 males, mean age 25.7, S.D. 5.3) before and after immersing the feet in ice-cold water (2 °C) for 30 min to evaluate the role of plantar insensitivity on gait patterns. Following ice water immersion, there was a significant decrease in walking speed. Maximum forces and peak pressures under the foot decreased, with the exception of an increase in loading under the third to fifth metatarsal heads. Contact times increased under all regions of the foot, and force–time and pressure–time integrals increased under the second and third to fifth metatarsal head regions. It is concluded that plantar insensitivity significantly alters the distribution, duration, and to a lesser extent, the magnitude of forces and pressures under the foot when walking. These results suggest that in the neuropathic foot, gait changes caused by plantar insensitivity may be partly responsible for the redistribution and altered duration of loading, whereas the increase in the magnitude of forces and pressures are primarily due to other disease-related factors.     

Deformation of foot cross-section shapes during walking

To clarify the magnitude of shape change during walking, the shapes of four cross-sections (Forefoot, Instep, Navicular, and Heel) of the right foot during standing and walking were measured using a four-dimensional measurement system we developed (14 Hz) with an accuracy of ±0.5 mm. Images of the sole were measured using a high-speed video camera (120 Hz). Cross-section shapes and derived dimensions were compared between the standing condition, first peak (P1), and midstance valley of two peaks (MSV) of vGRF during walking. Heel and Navicular cross-sections were more laterally inclined during walking than during standing by 6° on average. Compared to at standing, breadth of the cross-section in contact with the ground was wider at the heel and instep at timing P1, and was wider at the forefoot and narrower at heel at timing MSV. Medial length was longer and dorsal arch was higher during walking than during standing. Plantar arch height did not differ between the three conditions. The maximum difference in plantar arch height between standing and P1 was 1.3 mm, much smaller than the inter-individual variation of 7 mm.     

Estimation of foot trajectory during human walking by a wearable inertial measurement unit mounted to the foot

To establish a supportive technology for reducing the risk of falling in older people, it is essential to clarify gait characteristics in elderly individuals that are possibly linked to the risk of falling during actual daily activities. In this study, we developed a system to monitor human gait in an outdoor environment using an inertial measurement unit consisting of a tri-axial accelerometer and tri-axial gyroscope. Step-by-step foot trajectories were estimated from the sensor unit attached to the dorsum of the foot. Specifically, stride length and foot clearance were calculated by integrating the gravity-compensated translational acceleration over time during the swing phase. Zero vertical velocity and displacement corrections were applied to obtain the final trajectory, assuming the slope of the walking surface is negligible. Short, normal, and long stride-length walking of 10 healthy participants was simultaneously measured using the proposed system and a conventional motion capture system to evaluate the accuracy of the estimated foot trajectory. Mean accuracy and precision were approximately 20 ± 50 mm, for stride length, and 2 ± 7 mm for foot clearance, indicating that the swing phase trajectory of the sensor unit attached to the foot was reconstructed more accurately and precisely using the proposed system than with previously published methods owing to the flat floor assumption. Although some methodological limitations certainly apply, this system will serve as a useful tool to monitor human walking during daily activities.     

Changes to foot pressure pattern in post-stroke individuals who have started to walk independently during the convalescent phase

BackgroundAbnormal foot contact patterns following stroke affect functional gait; however, objective analysis targeting independent walking is lacking.Research questionHow do walking abilities and foot pressure patterns differ between post-stroke individuals who achieved independent walking and healthy controls? Secondarily, how do the abilities and patterns in post-stroke individuals change before and after achieving independent walking? Can these changes become criteria for permitting independent walking?MethodsTwenty-eight individuals with hemiplegia and 32 controls were enrolled. Motor dysfunction score (MDScore), walking speed (WSpeed), and foot pressure patterns were measured when they were first able to walk without orthosis or physical assistance (1st assessment) and when they achieved independent walking around discharge (2nd assessment). Foot pressure patterns were measured using insole-type foot pressure-measuring system. Ratios of partial foot pressure to body weight (%PFP), ratios of anteroposterior length of center of pressure (COP; %Long), and backward moving distance of COP to the foot length (%Backward) were calculated. Parameters during the 2nd assessment were compared with those of controls and those during the 1st assessment. During the 2nd assessment, relationships among the parameters, MDScore, and WSpeed were analyzed.ResultsDuring the 2nd assessment, no difference was observed in both %Long and %Backward between the non-paretic limbs and the controls. While the %Backward was higher, the %PFP of toes and %Long were lower in the paretic limb than in the controls. Although the %Backward was lower, both %PFP of toes and %Long of the paretic limb were higher in the 2nd assessment than in the 1st assessment. During the 2nd assessment, both %Long and % Backward values of the paretic limb moderately correlated with MDScore and WSpeed.SignificanceAfter improvement of foot pressure in toes, both an increase in anteroposterior length and a decrease in backward moving of COP path were objective signs permitting independent walking.     

Real-time feedback as a method of monitoring walking velocity during gait analysis

When quantifying the mechanics of gait, it is important to ensure that subjects maintain a consistent walking velocity during gait analysis trials. Most methods of measuring walking velocity do not produce data until after the subject has completed the trial. This often results in discarding completed trials from analysis because the subject's velocity was not within an acceptable range. Real-time feedback of position data can be used to help subjects adjust their walking velocity during the trial, when necessary. Results from 14 subjects who participated in gait analysis using real-time feedback to monitor their walking velocity show that they were able to stay within an acceptable range of their target walking velocities (each subject's preferred velocity and 150% of their preferred velocity) during 90% and 80% of trials, respectively. This method allows for accurate and efficient data collections without the use of additional equipment.     

Impact of diabetic neuropathy severity on foot clearance complexity and variability during walking

BackgroundThe control of foot trajectory during swing phase is important to achieve safe clearance with the ground. Complexity of a physiological control system arises from the interaction of structural units and regulatory feedback loops that operate to enable the organism to adapt to a non-static environment. Diabetic polyneuropathy (DPN) impairs peripheral feedback inputs and alters ankle control during gait, which might affect toe clearance (ToC) parameters and its complexity, predisposing DPN-subjects to tripping and falling.Research questionHow do different DPN-severity degrees change ToC trajectory and minimum ToC, and its complexity during gait of diabetic subjects?Methods15 healthy controls and 69 diabetic subjects were assessed and classified into DPN-severity degrees by an expert fuzzy model: absent (n = 26), mild (n = 21) and severe (n = 22). Three-dimensional kinematics was measured during comfortable walking. ToC was the minimum vertical distance between the marker placed at the first metatarsal head and the ground during swing. Mean ToC, ToC standard deviation (SD) between trials, and sample entropy (SaEn) and standard deviation (SD) of ToC trajectory were calculated from the ToC temporal series. ANOVA and ANCOVA (with the walking speed as the covariate) and Bonferroni pairwise post-hoc tests (P < 0.05) were used to compare groups.ResultsMean ToC and ToC SD did not show differences between groups (ANCOVA F = 0.436; df = 3; P = 0.705; F=1.719; df=3; P=0.170, respectively). ToC trajectory SD also did not show differences between groups (ANCOVA F = 3.98; df = 3; P = 0.755). Severe-DPN subjects showed higher ToC_Traj_SaEn than controls (ANCOVA F=2.60; df=3; P = 0.05).SignificanceSevere-DPN subjects showed a more complex pattern of overall foot-ankle trajectory in swing phase in comparison to controls, although did not present lower minimum ToC values. The higher complexity of ToC might lead to an increase in the motor system output (more strategies, increase in variability), resulting in a more unstable system and selected motor strategies.     

Effect of customised preformed foot orthoses on gait parameters in children with juvenile idiopathic arthritis: A multicentre randomised clinical trial

BackgroundChildren with juvenile idiopathic arthritis (JIA) can experience significant physical impairment of the lower extremity. Prolonged joint disease and symptoms may cause gait alterations such as reduced walking speed and increased plantar pressures in diseased areas of their feet. There is limited robust clinical trials investigating the effect of non-invasive mechanical therapies such as foot orthoses (FOs) on improving gait parameters in children with JIA.Research questionAre customised preformed FOs effective in improving gait parameters in children with JIA?MethodsA multicentre, parallel design, single-blinded randomised clinical trial was used to assess the gait impacts of customised preformed FOs on children with JIA. Children with a diagnosis of JIA, exhibiting lower limb symptoms and aged 5–18 were eligible. The trial group received a low-density full length, Slimflex Simple device which was customised chair side and the control group received a sham device. Peak pressure and pressure time integrals were used as the main gait outcomes and were measured using portable Tekscan gait analysis technology at baseline, 3 and 6 months. Differences at each follow-up were assessed using the Wilcoxon rank sum test.Results66 participants were recruited. Customised preformed FOs were effective in altering plantar pressures in children with JIA versus a control device. Reductions of peak pressures and pressure time integrals in the heel, forefoot and 5th metatarsophalangeal joint were statistically significant in favour of the trial group. This was associated with statistically significant increased midfoot contact with the trial device at baseline, 3 and 6-month data collections. The trial intervention was safe and well accepted by participants, which is reflected in the high retention rate (92%).SignificanceClinicians may prescribe customised preformed FOs in children with JIA to deflect pressure from painful joints and redistribute from high pressure areas such as the rearfoot and forefoot.     

A model to calculate the progression of the centre of pressure under the foot during gait analysis

Pedobarography and the centre of pressure (COP) progression is useful to understand foot function. Pedobarography is often unavailable in gait laboratories or completed asynchronously to kinematic and kinetic data collection. This paper presents a model that allows calculation of COP progression synchronously using force plate data. The model is an adjunct to Plug-In-Gait and was applied to 49 typically developing children to create reference COP data. COP progressions were noted to spend 8% of stance behind the ankle joint centre, traverse lateral of the longitudinal axis of the foot through the midfoot for 76% of stance and finishing past the second metatarsal head on the medial side for 16% of stance. It is hoped the model will bridge the information gap for gait laboratories lacking pedobarography during foot assessments and will open up the possibility of retrospective research into COP progression based indices on kinematic data.     

Center of pressure trajectory during gait: A comparison of four foot positions

Knowledge of the center of pressure (COP) trajectory during stance can elucidate possible foot pathology, provide comparative effectiveness of foot orthotics, and allow for appropriate calculation of balance control and joint kinetics during gait. Therefore, the goal of this study was to investigate the COP movement when walking at self-selected speeds with plantigrade, equinus, inverted, and everted foot positions. A total of 13 healthy subjects were asked to walk barefoot across an 8-m walkway with embedded force plates. The COP was computed for each stance limb using the ground reaction forces and moments collected from three force plates. Results demonstrated that the COP excursion was 83% of the foot length and 27% of the foot width in the anterior–posterior and medial lateral directions for plantigrade walking, respectively. Regression equations explained 94% and 44% of the anterior–posterior and medial–lateral COP variability during plantigrade walking, respectively. While the range of motion and COP velocity were similar for inverted and everted walking, the COP remained on the lateral and medial aspects of the foot for these two walking conditions, respectively. A reduced anterior–posterior COP range of motion and velocity were demonstrated during equinus walking. Ankle joint motion in the frontal and sagittal planes supported this COP movement, with increased inversion and plantar flexion demonstrated during inverted and equinus conditions, respectively. Results from this study demonstrated the COP kinematics during simulated pathological gait conditions, with the COP trajectory providing an additional tool for the evaluation of patients with pathology.     

Center of pressure trajectory during gait: A comparison of four foot positions

Knowledge of the center of pressure (COP) trajectory during stance can elucidate possible foot pathology, provide comparative effectiveness of foot orthotics, and allow for appropriate calculation of balance control and joint kinetics during gait. Therefore, the goal of this study was to investigate the COP movement when walking at self-selected speeds with plantigrade, equinus, inverted, and everted foot positions. A total of 13 healthy subjects were asked to walk barefoot across an 8-m walkway with embedded force plates. The COP was computed for each stance limb using the ground reaction forces and moments collected from three force plates. Results demonstrated that the COP excursion was 83% of the foot length and 27% of the foot width in the anterior–posterior and medial lateral directions for plantigrade walking, respectively. Regression equations explained 94% and 44% of the anterior–posterior and medial–lateral COP variability during plantigrade walking, respectively. While the range of motion and COP velocity were similar for inverted and everted walking, the COP remained on the lateral and medial aspects of the foot for these two walking conditions, respectively. A reduced anterior–posterior COP range of motion and velocity were demonstrated during equinus walking. Ankle joint motion in the frontal and sagittal planes supported this COP movement, with increased inversion and plantar flexion demonstrated during inverted and equinus conditions, respectively. Results from this study demonstrated the COP kinematics during simulated pathological gait conditions, with the COP trajectory providing an additional tool for the evaluation of patients with pathology.     

The impact of body fat on three dimensional motion of the paediatric foot during walking

Childhood obesity is commonly associated with a pes planus foot type and altered lower limb joint function during walking. However, limited information has been reported on dynamic intersegment foot motion with the level of obesity in children. The aim of this study was to explore the relationships between intersegment foot motion during gait and body fat in boys age 7–11 years.Fat mass was measured in fifty-five boys using air displacement plethysmography. Three-dimensional gait analysis was conducted on the right foot of each participant using the 3DFoot model to capture angular motion of the shank, calcaneus, midfoot and metatarsals. Two multivariate statistical techniques were employed; principle component analysis reduced the multidimensional nature of gait analysis, and multiple linear regression analysis accounted for potential confounding factors.Higher fat mass predicted greater plantarflexion of the calcaneus during the first half and end of stance phase and at the end of swing phase. Greater abduction of the calcaneus throughout stance and swing was predicted by greater fat mass. At the midfoot, higher fat mass predicted greater dorsiflexion and eversion throughout the gait cycle.The findings present novel information on the relationships between intersegment angular motion of the foot and body fat in young boys. The data indicates a more pronated foot type in boys with greater body fat. These findings have clinical implications for pes planus and a predisposition for pain and discomfort during weight bearing activities potentially reducing motivation in obese children to be physically active.     

In-shoe plantar pressure measurements for the evaluation and adaptation of foot orthoses in patients with rheumatoid arthritis: A proof of concept study

ObjectivesImproving foot orthoses (FOs) in patients with rheumatoid arthritis (RA) by using in-shoe plantar pressure measurements seems promising. The objectives of this study were to evaluate (1) the outcome on plantar pressure distribution of FOs that were adapted using in-shoe plantar pressure measurements according to a protocol and (2) the protocol feasibility.MethodsForty-five RA patients with foot problems were included in this observational proof-of concept study. FOs were custom-made by a podiatrist according to usual care. Regions of Interest (ROIs) for plantar pressure reduction were selected. According to a protocol, usual care FOs were evaluated using in-shoe plantar pressure measurements and, if necessary, adapted. Plantar pressure–time integrals at the ROIs were compared between the following conditions: (1) no-FO versus usual care FO and (2) usual care FO versus adapted FO. Semi-structured interviews were held with patients and podiatrists to evaluate the feasibility of the protocol.ResultsAdapted FOs were developed in 70% of the patients. In these patients, usual care FOs showed a mean 9% reduction in pressure–time integral at forefoot ROIs compared to no-FOs (p = 0.01). FO adaptation led to an additional mean 3% reduction in pressure–time integral (p = 0.05). The protocol was considered feasible by patients. Podiatrists considered the protocol more useful to achieve individual rather than general treatment goals. A final protocol was proposed.ConclusionsUsing in-shoe plantar pressure measurements for adapting foot orthoses for patients with RA leads to a small additional plantar pressure reduction in the forefoot. Further research on the clinical relevance of this outcome is required.     

Evaluation of early walking patterns from plantar pressure distribution measurements. First year results of 42 children

This study evaluated developmental changes of foot and gait during the first year of independent walking. In a longitudinal design, plantar pressure distribution patterns were measured with a capacitive platform every 3 months in a group of 42 normal children. The first significant changes were already found after a few weeks of independent walking. The development of the longitudinal arch correlated with significantly reduced midfoot loading parameters even though the changes showed a wide interindividual variation. This study illustrates that a child's foot goes through significant changes in shape and loading characteristics once the child starts to stand and walk. Some children showed a fairly mature appearance of the plantar pressure pattern after 1 year while others retained a more immature loading pattern.     

Longitudinal profiles of oxygen uptake during treadmill walking in able-bodied children: the locomotion energy and growth study

The purpose of this study was to document age-related changes in walking V_O2 in able-bodied boys and girls. Beginning at age 6 and ending at age 10, 23 children (14 girls, 9 boys) performed six 5-min bouts of level treadmill walking at 0.67, 0.89, 1.12, 1.34, 1.56, and 1.79 m s⁻¹ on an annual basis. Prior to data collection, subjects received 60 min of treadmill walking practice. During the last 2 min of each walking bout, a 2-min sample of expired air was collected in a meteorological balloon and analyzed to determine V_O2. Averaged across age, interindividual variation in V_O2 ranged from 32 to 41%. Repeated-measures analysis of variance demonstrated a speed by age interaction for V_O2, such that mean V_O2 rose (P≤0.05) across the five fastest speeds for 6-, 7-, 8-, and 10-year olds and increased over the entire speed range for 9-year olds. For all speeds, V_O2 decreased yearly from the ages of 6 to 8. When averaged across speeds, V_O2 was 27% higher for 6-year olds compared with 10-year olds. From a clinical perspective, access to longitudinal measurements of walking V_O2 in able-bodied children should be helpful in interpreting gait energy use in children with movement disorders and evaluating treatment strategies designed to reduce the aerobic demand of locomotion in youth with impaired mobility.     

Biomechanics of the infant foot during the transition to independent walking: A narrative review

Recognising structural and functional development of the paediatric foot is fundamental to ensuring a strong theoretical framework for health professionals and scientists. The transition of an infant from sitting to walking takes approximately 9 months and is when the structures and function of the foot must respond to the challenges of bearing load; becoming increasingly more essential for locomotion. Literature pertaining to the phase of development was searched. A narrative approach synthesised the information from papers written in English, with non-symptomatic infant participants up to the development stage of independent walking or two years of age. A range of literature was identified documenting morphological, physiological, neuromuscular and biomechanical aspects of the infant within this phase of development. The progression of variable gait to a regular pattern is documented within a range of studies focusing on neuromuscular control and ambulation development. However, methodological approaches may have compromised the external validity of such data. Additionally, limited consideration for the specific function and development of the foot is evident, despite its role as the primary site of weight bearing and interface with the floor. A lack of consideration of infants prior to ambulation (i.e. before cruising or walking) is also apparent which prevents a reference baseline being used effectively. This review also identifies future research priorities such that a comprehensive understanding of foot development from a non-weight bearing to a weight bearing structure during locomotor advancement can be gained.     

Foot pronation during walking is associated to the mechanical resistance of the midfoot joint complex

BackgroundThe demonstration of the relationship between midfoot passive mechanical resistance and foot pronation during gait may guide the development of assessment and intervention methods to modify foot motion during gait and to alter midfoot passive mechanical resistance.Research questionIs foot pronation during the stance phase of gait related to the midfoot passive mechanical resistance to inversion?MethodsThe resistance torque and stiffness provided by midfoot soft tissues of 33 participants (21 females and 12 males) with average of 26.21 years were measured. In addition, the participants’ forefoot and rearfoot kinematic data during the stance phase of gait were collected with the Qualisys System (Oqus 7+). Correlation Coefficients were calculated to test the association between kinematic variables representing pronation (forefoot-rearfoot inversion, forefoot-rearfoot dorsiflexion and rearfoot-shank eversion) and maximum resistance torque and maximum stiffness of the midfoot with α = 0.05.ResultsReduced maximum midfoot resistance torque was moderately associated with increased forefoot-rearfoot inversion peak (p = 0.029; r = 0.38), with forefoot-rearfoot dorsiflexion peak (p = 0.048; r = −0.35) and with rearfoot-shank eversion peak (p = 0.008; r = −0.45). Maximum midfoot stiffness was not associated to foot pronation.SignificanceThe smaller the midfoot resistance torque, the greater the forefoot-rearfoot inversion and dorsiflexion peaks and the rearfoot-shank eversion peak during gait. The findings suggest the existence of a relationship between foot pronation and midfoot passive mechanical resistance. Thus, changes in midfoot passive mechanical resistance may affect foot pronation during gait.     

The trajectory of the centre of pressure during barefoot running as a potential measure for foot function

The main purpose of this study was to describe and interpret the COP trajectory during barefoot running in a large cohort of young adults with no history of injury. COP data were collected from 215 subjects, who ran at 3.3 m s⁻¹ over a 16.5 m long track, with a built in Footscan^® pressure platform. COP data were filtered using a 50 Hz lowpass butterworth filter and normalised. Reliability was then studied and mean curves were calculated for medial–lateral displacement (COP_x) and velocity (v_xCOP), anterior–posterior displacement (COP_y) and velocity (v_yCOP) as well as for the resultant velocity (v_xyCOP). Displacement and velocity of the COP provided insight over functional foot behaviour. A medially oriented peak in v_xCOP was found, which may reflect the fast initial pronation. A laterally oriented second peak in v_xCOP, together with a second peak in v_yCOP, indicated a fast forward shift of the COP over the lateral border of the foot during forefoot contact phase. During the forefoot push off phase, at the level of the metatarsals, anterior velocities of the COP were low and reflected the importance of the forefoot during push off. Finally, the COP course was studied for high arch, normal and low arch feet and indicated, a more lateral COP course for the low arch feet.