A comparison of vertical force and temporal parameters produced by an in-shoe pressure measuring system and a force platform

Characterization of the Kinetyx SI Wireless Pressure-Measuring Insole during Benchtop Testing and Running Gait

This study characterized the absolute pressure measurement error and reliability of a new fully integrated (Kinetyx, SI) plantar-pressure measurement system (PPMS) versus an industry-standard PPMS (F-Scan, Tekscan) during an established benchtop testing protocol as well as via a research-grade, instrumented treadmill (Bertec) during a running protocol. Benchtop testing results showed that both SI and F-Scan had strong positive linearity (Pearson's correlation coefficient, PCC = 0.86-0.97, PCC = 0.87-0.92; RMSE = 15.96 ± 9.49) and mean root mean squared error RMSE (9.17 ± 2.02) compared to the F-Scan on a progressive loading step test. The SI and F-Scan had comparable results for linearity and hysteresis on a sinusoidal loading test (PCC = 0.92-0.99; 5.04 ± 1.41; PCC = 0.94-0.99; 6.15 ± 1.39, respectively). SI had less mean RMSE (6.19 ± 1.38) than the F-Scan (8.66 ±2.31) on the sinusoidal test and less absolute error (4.08 ± 3.26) than the F-Scan (16.38 ± 12.43) on a static test. Both the SI and F-Scan had near-perfect between-day reliability interclass correlation coefficient, ICC = 0.97-1.00) to the F-Scan (ICC = 0.96-1.00). During running, the SI pressure output had a near-perfect linearity and low RMSE compared to the force measurement from the Bertec treadmill. However, the SI pressure output had a mean hysteresis of 7.67% with a 28.47% maximum hysteresis, which may have implications for the accurate quantification of kinetic gait measures during running.

INSOLE-BASED ESTIMATION OF COMPLETE GROUND REACTION FORCE WITH GAUSSIAN KERNEL REGRESSION AND DATA EXPANSION

A method for estimating ground reaction force (GRF) with plantar pressure was proposed in this paper. The estimation model was constructed to approximate the nonlinear relationships between GRF and the plantar pressure according to the linear combinations of Gaussian kernel functions. Partial least squares regression (PLSR) was adopted to obtain model parameters and eliminate multicollinearity among the pressure components. The general model and subject-specific models were constructed for 12 male and 4 female subjects. Moreover, a data expansion method was introduced for the establishment of subject-specific model, which is implemented by searching and adopting the data with consistent statistical characteristics in a pre-established database. That approach is particularly meaningful for the group whose walking ability is limited or clinic where the force platform is not available. The NRMSEs (%) for general model were 5.27–7.85% (GRF_V), 7.35–8.53% (GRF_ML), and 8.82–10.54% (GRF_AP). The maximum NRMSEs (%) for subject-specific models were 5.02% (GRF_V), 9.91% (GRF_ML), and 10.23% (GRF_AP). Results showed that both general and subject-specific models achieved higher accuracy than existing methods such as linear regression and neural network methods.

The immediate effects of hallux valgus orthoses: A comparison of orthosis designs

BACKGROUND

Hallux valgus orthoses are available in a wide range of designs and materials, but the effects of their design on functional performance have not been fully investigated.

RESEARCH QUESTION

This present study aims to comprehensively analyze the immediate effects of soft and semi-rigid hallux valgus orthoses on balance, plantar pressure, hallux valgus angle, and subjective sensations.

METHODS

Sixteen female subjects have participated in the study, including 10 subjects with healthy feet and 6 with hallux valgus. Three conditions are tested, including in the barefoot and using two types of commercially available hallux valgus orthoses. The subjects participate in static and dynamic (walking) tests with the use of the Novel Pedar® system. The peak pressure values in the hallux, lateral toes, first metatarsophalangeal joint, 2-4th metatarsal heads, 5th metatarsal head, medial midfoot, lateral midfoot and rearfoot in the various foot conditions are examined and compared. The hallux valgus angle of each subject is measured based on their footprint. Their subjective feelings towards the orthoses are also evaluated. A repeated-measures analysis of variance, and independent-sample t-test are performed.

RESULTS

The correction of the hallux valgus angle is statistically significant when the subjects with hallux valgus use the orthoses. In comparing the two types of orthoses, the use of the orthosis made of soft materials results in correction in the hallux valgus angle and higher wear comfort, and lower plantar pressure in hallux area.

SIGNIFICANCE

The results provide insights into the design of hallux valgus orthoses, thus offering practical reference for the selection of hallux valgus orthosis with compromise between functional performance and wear comfort.

Predicting Ground Reaction Force from a Hip-Borne Accelerometer during Load Carriage

INTRODUCTION

Ground reaction forces (GRF) during load carriage differ from unloaded walking. Methods to quantify peak vertical GRF (pGRFvert) of Soldiers walking with loads outside of a laboratory are needed to study GRF during operationally relevant tasks.

PURPOSE

Develop a statistically based model to predict pGRFvert during loaded walking from ActiGraph GT3X+ activity monitor (AM) vertical acceleration.

METHODS

Fifteen male Soldiers (25.4 ± 5.3 yr, 85.8 ± 9.2 kg, 1.79 ± 9.3 m) wore an ActiGraph GT3X+ AM over their right hip. Six walking trials (0.67-1.58 m·s) with four loads (no load, 15, 27, 46 kg) and two types of footwear (athletic shoes and combat boots) were completed on an instrumented force plate treadmill. Average peak vertical AM acceleration (pACCvert) and pGRFvert were used to develop a regression equation to predict pGRFvert. The model was validated using a leave-one-subject-out approach. Root mean square error (RMSE) and average absolute percent difference (AAPD) between actual and predicted pGRFvert were determined. pGRFvert was also predicted for two novel data sets and AAPD and RMSE calculated.

RESULTS

The final equation to predict pGRFvert included pACCvert, body mass, carried load mass, and pACCvert-carried load mass interaction. Cross-validation resulted in an AAPD of 4.0% ± 2.7% and an RMSE of 69.5 N for leave-one-subject-out and an AAPD of 5.5% ± 3.9% and an RMSE of 78.7 N for the two novel data sets.

CONCLUSION

A statistically based equation developed to predict pGRFvert from ActiGraph GT3X+ AM acceleration proved to be accurate to within 4% for Soldiers carrying loads while walking. This equation provides a means to predict GRF without a force plate.

Fifth metatarsal stress fracture in elite male football players: an on-field analysis of plantar loading

Objective

Evaluate plantar loading during ‘on-field’ common football movements in players after fifth metatarsal (MT-5) stress fracture and compare with matched healthy players.

Methods

Fourteen elite male soccer players participated in the study conducted on a natural grass playing surface using firm ground football boots. Seven players who had suffered a primary stress fracture (MT-5 group) and seven matched healthy players (controls, CON) performed three common football movements while in-shoe plantar loading data were collected.

Results

Large between-group differences exist for maximal vertical force normalised to bodyweight (F_max) at the lateral toes (2-5) of the stance leg during a set-piece kick (MT-5: 0.2±0.06 bodyweight (BW), CON: 0.1±0.05 BW, effect size (ES) 1.4) and the curved run where the MT-5 group showed higher F_max with very large effect size at the lateral forefoot of the injured (closest to curve) limb when running a curve to receive a pass (MT-5 injured−CON=0.01 BW, ES 1.5). Small between-group differences were evident during straight-line running. However, between-limb analysis of MT-5 group showed significant unloading of the lateral forefoot region of the involved foot.

Conclusions

Elite male football players who have returned to play after MT-5 stress fracture display significantly higher maximum plantar force at the lateral forefoot and lateral toes (2-5) compared with healthy matched control players during two football movements (kick and curved run) with the magnitude of these differences being very large. These findings may have important implications for manipulating regional load during rehabilitation or should a player report lateral forefoot prodromal symptoms.

Validation of Moticon's OpenGo sensor insoles during gait, jumps, balance and cross-country skiing specific imitation movements

The purpose of this study was the experimental validation of the OpenGo sensor insole system compared to PedarX sensor insole and AMTI force-plate systems. Sixteen healthy participants performed trials in walking, running, jumping (drop and counter movement jumps), imitation drills and balance, with simultaneous measures of all three systems. Detected ground contact and flight times with OpenGo during walking, running and jumping were similar to those of AMTI. Force–time curves revealed comparable shapes between all three systems. Force impulses were 13–34% lower with OpenGo when compared to AMTI. Despite differences in mean values in some exercise modes, correlations towards AMTI were between r = 0.8 and r = 1.0 in most situations. During fast motions, with high force and impact, OpenGo provided lower force and latency in force kinetics. During balance tasks, discrepancy in the centre of pressure was found medio-lateral, while anterio–posterior direction was closer to AMTI. With awareness of these limitations, OpenGo can be applied in both clinical and research settings to evaluate temporal, force and balance parameters during different types of motion. The fully mobile OpenGo system allows for the easy and quick system application, analysis and feedback under complex field conditions, as well.

Pain sensitization and degenerative changes are associated with aberrant plantar loading in patients with painful knee osteoarthritis

OBJECTIVES

This study focused on the biomechanical implications of knee osteoarthritis (OA) and the association with pain. The plantar loading force distribution of the foot was determined and correlated to degenerative knee changes, function, pain intensity, and pain sensitization.

METHOD

Knee OA patients (n = 34) with moderate and mild knee pain were characterized and compared to matched controls (n = 16). The Plantar Foot Posture Index (FPI) and mean maximum plantar forces were determined by pressure-sensitive insoles. Pain intensity and function were assessed by the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Brief Pain Inventory (BPI). Local knee pain sensitization was assessed by pressure pain thresholds (PPTs) from eight knee locations. Spreading sensitization was assessed by PPTs from two extra-segmental test sites. Temporal summation to repeated pressure stimulation (knee and extra-segmental stimulation) and conditioning pain modulation (CPM) were assessed, representing central pain mechanisms.

RESULTS

The maximum force (MF) applied by the medial forefoot correlated to knee PPTs (r = 0.524, p < 0.001), CPM potency (r = 0.532, p < 0.001), and BPI (r = -0.325, p < 0.05) and WOMAC scores (pain r = -0.425, p < 0.01; stiffness r = -0.386, p < 0.01; function r = -0.378, p < 0.05). The MF applied by the medial hindfoot correlated negatively to scores on the FPI (r = -0.394, p < 0.01) and the Kellgren-Lawrence (K-L) grading scale (r = -0.330, p < 0.05). The MF applied by the medial forefoot correlated to extra-segmental PPTs (r = 0.554, p < 0.001) and the potency of CPM (r = 0.561, p < 0.0001). The MF applied by the lateral hindfoot correlated negatively to the PPT assessed extra-segmentally (r = -0.367, p < 0.05) and positively to CPM potency (r = 0.322, p < 0.05).

CONCLUSIONS

This study shows that mean maximum plantar foot force distribution in patients with painful knee OA is associated with specific pain mechanisms, function, radiological findings, and pain intensity.

Reliability and validity of pressure and temporal parameters recorded using a pressure-sensitive insole during running

Running biomechanics has received increasing interest in recent literature on running-related injuries, calling for new, portable methods for large-scale measurements. Our aims were to define running strike pattern based on output of a new pressure-sensitive measurement device, the Runalyser, and to test its validity regarding temporal parameters describing running gait. Furthermore, reliability of the Runalyser measurements was evaluated, as well as its ability to discriminate different running styles. Thirty-one healthy participants (30.3 ± 7.4 years, 1.78 ± 0.10 m and 74.1 ± 12.1 kg) were involved in the different study parts. Eleven participants were instructed to use a rearfoot (RFS), midfoot (MFS) and forefoot (FFS) strike pattern while running on a treadmill. Strike pattern was subsequently defined using a linear regression (R(2)=0.89) between foot strike angle, as determined by motion analysis (1000 Hz), and strike index (SI, point of contact on the foot sole, as a percentage of foot sole length), as measured by the Runalyser. MFS was defined by the 95% confidence interval of the intercept (SI=43.9-49.1%). High agreement (overall mean difference 1.2%) was found between stance time, flight time, stride time and duty factor as determined by the Runalyser and a force-measuring treadmill (n=16 participants). Measurements of the two devices were highly correlated (R ≥ 0.80) and not significantly different. Test-retest intra-class correlation coefficients for all parameters were ≥ 0.94 (n=14 participants). Significant differences (p<0.05) between FFS, RFS and habitual running were detected regarding SI, stance time and stride time (n=24 participants). The Runalyser is suitable for, and easily applicable in large-scale studies on running biomechanics.

Strength asymmetry increases gait asymmetry and variability in older women

PURPOSE

The aim of the research was to determine how knee extensor strength asymmetry influences gait asymmetry and variability because these gait parameters have been related to mobility and falls in older adults.

METHODS

Strength of the knee extensors was measured in 24 older women (65-80 yr). Subjects were separated into symmetrical strength (SS, n = 13) and asymmetrical strength (SA, n = 11) groups using an asymmetry cutoff of 20%. Subjects walked at a standard speed of 0.8 m·s and at maximal speed on an instrumented treadmill while kinetic and spatiotemporal gait variables were measured. Gait and strength asymmetry were calculated as the percentage difference between legs and gait variability as the coefficient of variation over 20 sequential steps.

RESULTS

SA had greater strength asymmetry (27.4% ± 5.5%) than SS (11.7% ± 5.4%, P < 0.001). Averaged across speeds, SA had greater single- (7.1% vs. 2.5%) and double-limb support time asymmetry (7.0% vs. 4.3%) than SS and greater single-limb support time variability (9.7% vs. 6.6%, all P < 0.05). Group × speed interactions occurred for weight acceptance force variability (P = 0.02) and weight acceptance force asymmetry (P = 0.017) with greater variability at the maximal speed in SA (5.0% ± 2.4% vs. 3.7% ± 1.2%) and greater asymmetry at the maximal speed in SA (6.4% ± 5.3% vs. 2.5% ± 2.3%).

CONCLUSION

Gait variability and asymmetry are greater in older women with strength asymmetry and increase when they walk near their maximal capacities. The maintenance of strength symmetry, or development of symmetry through unilateral exercise, may be beneficial in reducing gait asymmetry, gait variability, and fall risk in older adults.

In-shoe plantar pressure measurements for patients with knee osteoarthritis: Reliability and effects of lateral heel wedges

Although plantar pressure measurement systems are being used increasingly during gait analyses to investigate foot orthotics, there is limited information describing test-retest reliability of such measurements. Objectives of this study were to (1) examine the test-retest reliability of lateral heel pressure (LHP) and centre of pressure (COP) during walking with and without lateral heel wedges, and (2) evaluate the effects of 4° and 8° lateral heel wedges on the magnitude of LHP, the pathway of the COP and the peak external knee adduction moment (KAM) in subjects with and without knee osteoarthritis (OA). Twenty-six subjects, 12 patients with knee OA and 14 healthy subjects, were evaluated during three lateral heel wedge conditions (control, 4° and 8°) with standardized footwear. Three-dimensional analyses of gait with optical motion capture, floor-mounted force plate and in-shoe plantar pressure were completed on two occasions. Intraclass correlation coefficients (ICC(2, 1)) for LHP were excellent (0.79-0.83) while ICCs for COP in the medial-lateral and anterior-posterior directions were more variable (0.66-0.86). Reliability was slightly diminished when using heel wedges. Standard errors of measurement suggested considerable day-to-day variability in an individual's measures. Lateral heel wedges significantly (p<0.001) increased LHP, shifted COP anteriorly and laterally, and decreased the KAM. No significant differences were observed between subjects with and without OA. Although the day-to-day variability appears too large to confidently evaluate changes in individual patients, and decreases in reliability with increases in wedge size indicate caution, these results suggest in-shoe measurement of LHP and COP are appropriate for use in studies evaluating biomechanical effects of foot orthoses for knee OA.

Computational techniques for using insole pressure sensors to analyse three-dimensional joint kinetics

This study evaluated the feasibility of using insole pressure sensors together with whole body dynamics to analyse joint kinetics while running. Local affine transformations of shoe kinematics were first used to track the position of insole sensors during locomotion. Centre of pressure estimates derived from the insoles were within 10 mm of forceplate measures through much of stance, while vertical force estimates were within 15% of peak forceplate recordings. Insole data were then coupled with a least squares whole body dynamic model to obtain shear force estimates that were comparable to forceplate records during running. We demonstrated that these techniques provide a viable approach for analysing joint kinetics when running on uninstrumented surfaces.

An insole sensor for recording weight bearing behavior during tibial fracture rehabilitation

Partial weight bearing prescriptions for tibial fracture care are made with little data to support their efficacy. To provide long term tibial load data that can be used to study, guide, and monitor partial weight bearing, we developed a novel load sensor that can record the load placed on an injured limb over a two-week period of time. The prototype load sensor demonstrated high linearity, low hysteresis and low static and dynamic drift. Preliminary human testing on the load sensor demonstrated the ability of the load sensor to capture load profile during underfoot recording. Presented are the bench testing and human testing data on the prototype load sensor verifying the design of an economic and durable system that allows for 2 weeks of recording of normal loads experienced by the tibia. This design motivates a next generation approach for use in clinical trials that will enable clinicians and researchers to improve current partial weight bearing prescriptions, thus improving tibial fracture outcomes.

The effects of fatigue on plantar pressure distribution in walking

The purpose of this study was to assess plantar pressure deviations due to fatigue. Plantar pressure was assessed using a portable system while eleven healthy subjects performed three walking tests, one before, one immediately after and another 30-min after intensive running. Pressure peak, intra-subject coefficient of variation and relative impulse were recorded. Significant decrease in pressure peak and the relative impulse under the heel and the midfoot along with significant increase in pressure peak and relative impulse under the forefoot were observed 30 min after the run. After a 30-min rest, the heel and forefoot loading remained significantly affected compared to the pre-test conditions while variability, step length and frequency remained unchanged. The study demonstrates short- and long-term plantar pressure deviations due to fatigue induced by an intensive 30-min run, while previous studies showed negligible deviation of the ground reaction force.

Reducing plantar pressure in rheumatoid arthritis: a comparison of running versus off-the-shelf orthopaedic footwear

BACKGROUND

Foot pain in patients with rheumatoid arthritis is common and can be associated with excessive forefoot plantar pressure loading. Running and off-the-shelf orthopaedic footwear are commonly recommended to manage foot pain and discomfort in these patients. The aim of this study was to evaluate the effect of running footwear as an alternative to off-the-shelf orthopaedic footwear on plantar pressure loading characteristics in people with forefoot pain associated with rheumatoid arthritis.

METHODS

Twenty participants diagnosed with rheumatoid arthritis reporting chronic forefoot pain participated in this experimental, randomised, single-blind, cross-over trial of three footwear conditions: control, running and off-the-shelf orthopaedic. Outcome measures included measurement of peak pressure and pressure-time integral, with an in-shoe plantar pressure measurement system, beneath the total foot, forefoot, midfoot and rearfoot. Furthermore, perceived comfort and footwear acceptability were determined for each footwear condition.

FINDINGS

Compared to the control footwear, forefoot peak pressures were reduced by 36% in the running footwear and by 20% in the orthopaedic footwear, compared to the control (P<0.001). Forefoot pressure-time integrals were reduced by 33% in the running footwear and by 23% in the orthopaedic footwear (P<0.001). The largest reductions were achieved with the running footwear across the whole plantar surface of the foot. Perceived comfort did not differ between running and orthopaedic footwear, although both were significantly more comfortable than the control footwear. Overall, more participants nominated the running footwear as the most acceptable footwear condition.

INTERPRETATION

The results of this preliminary study show that running footwear was most effective at reducing plantar pressure loading and was regarded as a comfortable and acceptable footwear alternative by participants with forefoot pain associated with rheumatoid arthritis.

Ambulatory assessment of ankle and foot dynamics

Ground reaction force (GRF) measurement is important in the analysis of human body movements. The main drawback of the existing measurement systems is the restriction to a laboratory environment. This paper proposes an ambulatory system for assessing the dynamics of ankle and foot, which integrates the measurement of the GRF with the measurement of human body movement. The GRF and the center of pressure (CoP) are measured using two six-degrees-of-freedom force sensors mounted beneath the shoe. The movement of foot and lower leg is measured using three miniature inertial sensors, two rigidly attached to the shoe and one on the lower leg. The proposed system is validated using a force plate and an optical position measurement system as a reference. The results show good correspondence between both measurement systems, except for the ankle power estimation. The root mean square (RMS) difference of the magnitude of the GRF over 10 evaluated trials was (0.012 +/- 0.001) N/N (mean +/- standard deviation), being (1.1 +/- 0.1)% of the maximal GRF magnitude. It should be noted that the forces, moments, and powers are normalized with respect to body weight. The CoP estimation using both methods shows good correspondence, as indicated by the RMS difference of (5.1 +/- 0.7) mm, corresponding to (1.7 +/- 0.3)% of the length of the shoe. The RMS difference between the magnitudes of the heel position estimates was calculated as (18 +/- 6) mm, being (1.4 +/- 0.5)% of the maximal magnitude. The ankle moment RMS difference was (0.004 +/- 0.001) Nm/N, being (2.3 +/- 0.5)% of the maximal magnitude. Finally, the RMS difference of the estimated power at the ankle was (0.02 +/- 0.005) W/N, being (14 +/- 5)% of the maximal power. This power difference is caused by an inaccurate estimation of the angular velocities using the optical reference measurement system, which is due to considering the foot as a single segment. The ambulatory system considers separate heel and forefoot segments, thus allowing an additional foot moment and power to be estimated. Based on the results of this research, it is concluded that the combination of the instrumented shoe and inertial sensing is a promising tool for the assessment of the dynamics of foot and ankle in an ambulatory setting.

Evaluation of instrumented shoes for ambulatory assessment of ground reaction forces

Currently, force plates or pressure sensitive insoles are the standard tools to measure ground reaction forces and centre of pressure data during human gait. Force plates, however, impose constraints on foot placement, and the available pressure sensitive insoles measure only one component of force. In this study, shoes instrumented with two force transducers measuring forces and moments in three dimensions were evaluated. Technical performance was assessed by comparing force measurement and centre of pressure reconstructions of the instrumented shoes against a force plate. The effect of the instrumented shoes on gait was investigated using an optical tracking system and a force plate. Instrumented shoes were compared against normal shoes and weighted shoes. The ground reaction force measured with force plate and instrumented shoes differed by 2.2+/-0.1% in magnitude and by 3.4+/-1.3 degrees in direction. The horizontal components differed by 9.9+/-3.8% in magnitude and 26.9+/-10.0 degrees in direction. Centre of pressure location differed by 13.7+/-2.4mm between measurement systems. A MANOVA repeated measures analysis on data of seven subjects, revealed significant differences in gait pattern between shoe types (p</=0.05). A subsequent univariate analysis showed significant differences only in maximum ground reaction force but these could not be attributed to specific shoe types by pair-wise comparison. This study indicates that shoes instrumented with force transducers can be a valuable alternative to current measurement systems if accurate sensing of position and orientation of the force transducers is improved. They are applicable in ambulatory settings and suitable for inverse dynamics analysis.

Alterations in plantar pressure with different walking boot designs

BACKGROUND

Specialized walking devices, such as total contact casts and removable walking boots, have been shown to be effective noninvasive treatment options for plantar ulcers. Attempts at improving patient compliance frequently lead to new boot designs; however, the effect of the design modifications on plantar pressures or on the contralateral limb often is unknown. The purpose of this study was to determine the effect of different walking-boot calf heights and rocker sole designs on regional plantar pressures, as well as, on contralateral limb loading during walking.

METHODS

Twenty-six subjects, 20 to 54 years of age, without foot pathology were tested using four different configurations: high calf, rocker sole (HCR); low calf, rocker sole (LCR); low calf, modified rocker sole (LCMR), and shoe. Peak pressures, pressure-time integrals, and contact areas were measured using the Novel Pedar-X insole pressure measurement system. Average peak force was calculated for the contralateral limb.

RESULTS

Greatest forefoot peak pressure reduction was found in the HCR group (37.3% reduction compared to shoe condition), followed by 31.6% and 19.8% in the LCR and LCMR groups, respectively (p<0.0001). Forefoot pressure-time integrals were reduced for HCR and LCR (22.1% and 21.5%, respectively) compared to the LCMR (13.0%) (p<0.0001).

CONCLUSIONS

Isolated modifications in walking boot designs resulted in plantar pressure modifications. LCR and LCMR designs favorably altered plantar pressures, but of a lesser magnitude than the HCR design. If lower calf, lower sole walking boot designs are recommended because of anticipated improvement in patient compliance, healing times may be prolonged.

Inverse dynamics calculations during gait with restricted ground reaction force information from pressure insoles

The number of consecutive strides that can be recorded in measurements of gait have been limited due to the number of force plates and dimensions of the measurement field. In addition, the feet are constrained to land on the force plates. A method to calculate the inverse dynamics from the motion and incomplete information from the ground reaction forces (GRF), vertical component and its application point, is presented and compared to the calculations based on force plate measurements. This method is based on the estimation of the three-dimensional GRF during walking with pressure insoles. RMS errors were lower than 20 W for knee joint power compared to those derived from force plate measurements. The errors were larger during double stance phase due to errors in the application point measured with the insoles. This method, with some technical improvement, could be implemented in new gait analysis protocols measuring several consecutive steps either on a treadmill or over ground, depending on the motion-measurement system, without constraining foot placement.

Validity of the Pedar Mobile system for vertical force measurement during a seven-hour period

Objective measurement of weight bearing during a long-term period can give insight into the postoperative loading of the lower extremity of orthopedic patients to avoid complications. This study investigated the validity of vertical ground reaction force measurements during a long-term period using the Pedar Mobile insole pressure system, by comparing it with a Kistler force platform. In addition, the validity of a new sensor drift correction algorithm to correct for offset drift in the Pedar signal was evaluated. Ground reaction force data were collected during dynamic and static conditions from five healthy subjects every hour for 7 h. A mean offset drift of 14.6% was found after 7 h. After applying the drift correction algorithm the Pedar system showed a high accuracy for the second peak in the ground reaction force-time curve (1.1 to 3.4% difference, p>0.05) and step duration (-2.0 to 4.4% difference, p>0.05). Less accuracy was found for the first peak in the ground reaction force-time curve (5.2 to 12.0% difference; p<0.05 for the first 3 h, p>0.05 for the last 4 h) and, consequently, in the vertical force impulse (5.5 to 11.0% difference, p>0.05). The Pedar Mobile system appeared to be a valid instrument to measure the vertical force during a long-term period when using the drift correction program described in this study.

Use of pressure insoles to calculate the complete ground reaction forces

A method to calculate the complete ground reaction force (GRF) components from the vertical GRF measured with pressure insoles is presented and validated. With this approach it is possible to measure several consecutive steps without any constraint on foot placement and compute a standard inverse dynamics analysis with the estimated GRF.

Techniques for measuring weight bearing during standing and walking

OBJECTIVE

To classify and assess techniques for measuring the amount of weight bearing during standing and walking.

BACKGROUND

A large variety of weight bearing measuring techniques exists. This review describes their advantages and limitations to assist clinicians and researchers in selecting a technique for their specific application in measuring weight bearing.

METHODS

A literature search was performed in Pubmed-Medline, CINAHL, and EMBASE. Measurement techniques were classified in 'clinical examination', 'scales', 'biofeedback systems', 'ambulatory devices' and 'platforms', and assessed on aspects of methodological quality, application, and feasibility.

RESULTS

A total of 68 related articles was evaluated. The clinical examination technique is a crude method to estimate the amount of weight bearing. Scales are useful for static measurements to evaluate symmetry in weight bearing. Biofeedback systems give more reliable, accurate and objective data on weight bearing compared to clinical examination and scales, but the high costs could limit their use in physical therapy departments. The ambulatory devices can measure weight bearing with good accuracy and reliability in the hospital and at home. Platforms have the best methodological quality, but are mostly restricted to a gait laboratory, need trained personnel, and are expensive.

CONCLUSIONS

The choice of a technique largely depends upon the criteria discussed in this review; however the clinical utilisation, the research question posed, and the available budget also play a role. The new developments seen in the field of 'ambulatory devices' are aimed at extending measuring time, and improved practicality in data collection and data analysis. For these latter devices, however, mainly preliminary studies have been published about devices that are not (yet) commercially available.