Force Platform Measurements Research Articles

Comparing Balance Performance on Force Platform Measures in Individuals with Parkinson's Disease and Healthy Adults.

Introduction Postural instability is a known contributing factor to balance dysfunction and increased fall risk in those with Parkinson's disease (PD). Computerized posturography employing a force platform system provides objective, quantitative assessments of postural control impairments. This study examines balance performance as measured by force platform (FP) tests in persons with PD compared to age-matched healthy adults. Secondarily, we examine if these FP measures provide diagnostic and clinically meaningful information about the underlying balance impairments in the PD population. Methods Participants—42 individuals with PD (Hoehn and Yahr stage = 2.33 ± 0.77) and 55 age-matched healthy adults—were assessed on three standardized balance measures on a computerized force platform system. Between groups, comparisons of FP performance were analyzed using independent t-test. Within the group, comparisons for the PD cohort were analyzed using ANOVA for comparing disease stage and Mann–Whitney U test for PD subtypes. Results The PD cohort demonstrated significantly greater postural instability on the sensory organization test (SOT) measures (P=0.013, CI-95% = 1.286 to 10.37) and slower movement velocity on the limits of stability (LOS) test (P=0.001, CI-95% = 0.597 to 1.595) than the healthy cohort, suggesting that these tests were sensitive to detect sensory integration and voluntary postural control deficits in the PD cohort. Within the PD group, the SOT differentiated between H&Y stages 1–3. The motor control test (MCT) detected changes in reactive postural control mainly in later disease stages. All three FP tests distinguished between PD subtypes, with the Posture Gait Instability subtype demonstrating poorer balance performance than Tremor Dominant subtype. Conclusion These findings suggest FP measures provide clinically meaningful, diagnostic information in the examination of balance impairments in individuals with PD. FP measures may inform clinicians regarding intrinsic balance deficits and guide them in designing targeted balance interventions to reduce fall risk in persons with PD.

Countermovement Jump Analysis Using Different Portable Devices: Implications for Field Testing

The aim of this study was to analyze the concurrent validity, test–retest reliability, and capacity to detect changes of four different portable devices used to measure a wide range of neuromuscular parameters derived from countermovement jump (CMJ). An accelerometric device (Myotest), a jump mat (Ergojump), an optical device (Optojump), and a smartphone app (MyJump) were simultaneously examined for concurrent validity against gold-standard measures (motion-capture system and a force platform). Twenty-two CMJ-derived variables were collected from 15 healthy male subjects (n = 60 CMJs). Contraction time (CT) and eccentric duration (EccD) measurements obtained from the Myotest were moderately to largely associated with and not different from force platform measurements (r = 0.31 to 0.64, ES = 0.11 to 0.18) and showed moderate test-retest reliability (intraclass correlation coefficient (ICC) = 0.92 to 0.97, coefficient of variation (CV) = 3.8 to 8.0%). Flight time (FT) and jump height (JH) from Ergojump, Optojump, and MyJump showed moderate to strong associations with gold-standard measurements (r = 0.57 to 0.98) and good test–retest reliability (ICC = 0.54 to 0.97, CV = 1.8 to 4.2). However, all portable devices underestimated JH (ES = 1.25 to 2.75). Independent of the instrument used, the analyzed CMJ variables showed good capacity to detect changes (standard error of measurement (SEM) < smallest worthwhile change (SWC)), with the exception of rate of force and rate of power development parameters, which showed marginal capacity (SEM > SWC). The Myotest is preferable to measure temporal parameters during ground contact, whereas Ergojump, Optojump, and MyJump devices may be preferable to measure FT and JH, with the Optojump being the most accurate.

Validity of a contact mat and accelerometric system to assess countermovement jump from flight time

ABSTRACTCountermovement jump (CMJ) height is an important parameter in physical performance. This study compared CMJ height measured using ChronoJump contact mat (CJ) and Myotest accelerometer (MT) systems with a force platform (FP). Thirty recreationally active adults (32.1 ± 10.4 years, 75.9 ± 12.0 kg, 173.2 ± 6.3 cm) completed a CMJ protocol where height was simultaneously recorded using the three systems. CJ and MT measures were strongly and significant correlated (r = 0.65, 0.66, respectively; p < 0.05) with FP. CJ-derived measures were not significantly different to FP measures (p > 0.05), yet MT-derived measures were significantly different from those obtained using the FP (p < 0.05). Systematic bias was observed between FP and the CJ and between FP and MT. This study demonstrates the validity of CJ and MT systems for the assessment of CMJ height. Systematic bias and between-device differences in measurement should be considered when interpreting and comparing data from these devices.

Axial reflexes are present in older subjects and may contribute to balance responses.

We studied the response to axial taps (mini-perturbations) of a group of 13 healthy older subjects (mean age 63 ± 12years, 7 females, 6 males), 12 of whom were also studied using larger applied (macro-) perturbations requiring active postural responses. The mini-perturbation consisted of a brief impulsive force produced by a mini-shaker applied to the trunk at the level of the shoulders and anteriorly at the upper sternum which was perceived as a tap. Acceleration, force platform, and EMG measurements were made. The average peak accelerations for the mini-perturbations were 108mG (anterior) and - 78.9mG (posterior). Responses overall were very similar to those previously reported for younger subjects: the perturbation evoked short latency responses in leg muscles, modulated by degree and direction of lean, and were largest for the muscle most relevant for the postural correction. The increases in the amplitude for the main agonist were greater than the increase in tonic activity. With both anterior and posterior lean, co-contraction responses were present. The size of the EMG response to the mini-perturbations correlated with the corresponding earliest EMG responses (0-100, 100-200ms intervals) to the larger postural perturbations, timing which corresponds to balance responses. The balance responses evoked by the larger imposed postural perturbations may, therefore, receive a contribution through the reflex pathway mediating the axial tap responses, whose efferent limb appears to be the reticulospinal tract.

Study of a C-wing configuration for passive drag and load alleviation

Non-planar wing configurations are often hypothesised as a means for improving the aerodynamic efficiency of large transport aircraft; C-wings may have the ability to exploit and unify drag reduction, aeroelasticity, and dynamics and control but their capacity to do so is ambiguous. The purpose of this work is to provide an experimental demonstration with the aim of verifying the C-wing configurations practical application. Thus, the main objective of this investigation is to quantify the C-wing’s ability for drag and load alleviation relative to a planar wing of equivalent wingspan, lift, and root bending moment at Re=1.5×106. Surface clay flow visualisations have been used to provide insight into the flow over the wing surface. Aerodynamic performance metrics show that despite the C-wing operating with a 19.1% higher wing wetted area, a peak total drag reduction of 9.5% at α=6° is achieved in addition to a 1.1% reduction in the wing root bending moment for equivalent lift. Force platform measurements in combination with laser vibrometry enabled a detailed understanding of the vibrational characteristics between the model and the wind tunnel. It is shown that the C-wing can passively attenuate buffet induced vibrations of the main-wing by up to 68.6% whilst simultaneously reducing total drag without a significant increase in wing weight or root bending moment.

Does the addition of two exercise-focussed home visits to usual care improve outcomes for patients with balance impairments? A randomized controlled trial

Objective: To investigate whether two additional home visits improve outcomes for rehabilitation outpatients with balance impairments compared to usual care. Design: Randomized controlled trial. Setting: Outpatient rehabilitation. Participants: Fifty with balance impairments. Interventions: Both groups received usual care including weekly group exercise over eight weeks. The intervention group received two home visits to individualize home exercises. Outcome measures: Primary outcome measure was the Balance Outcome Measure for Elder Rehabilitation (BOOMER) score, and secondary outcomes included force platform measures using the NeuroCom Balance Master®, assessed at baseline, after intervention and three-month follow-up. Results: There was no between-group difference for BOOMER score. There were significant between-group differences in favour of the intervention group for limits of stability reaction time at week 9 (mean difference (MD) −0.27, 95% confidence interval (CI) −0.44 to −0.09) and week 22 (MD −0.28, 95% CI −0.45 to −0.10) and for limits of stability maximal excursion at week 9 (MD 8.66, 95% CI 1.67 to 15.65) and week 22 (MD 14.58, 95% CI 7.59 to 21.57). Significant between-group differences favoured the control group for Clinical Test of Sensory Interaction of Balance at week 9 (MD 0.40, 95% CI 0.13 to 0.66) and week 22 (MD 0.45, 95% CI 0.18 to 0.72) and step quick turn time at week 9 (MD 0.56, 95% CI 0.02 to 1.10). Conclusion: Two exercise-focussed home visits improved some dynamic balance outcomes in older patients with balance impairments. Some outcomes showed significant improvements with small effect sizes in favour of the control group which may be chance findings or because they completed a standard home exercise programme.

Prediction of active peak force using a multilayer perceptron

Both kinematic parameters and ground reaction forces (GRFs) are necessary for understanding the biomechanics of running. Kinematic information of a runner is typically measured by a motion capture system whereas GRF during the support phase of running is measured by force platforms. To analyze both kinematics and kinetics of a runner over several subsequent contacts, an instrumented treadmill or alternatively several force platforms installed over a regulated space are available options, but they are highly immovable, expensive, and sometimes even impractical options. Naturally, it would be highly useful to predict GRFs using a motion capture system only and this way reduce costs and complexity of the analysis. In this study, the machine learning model for vertical GRF magnitude prediction based on running motion information of 128 healthy adults is proposed. The predicted outputs of a multilayer perceptron model were compared with the actual force platform measurements. The results were evaluated with Pearson’s correlation coefficient through a tenfold cross validation. The mean standard error of the estimate was 0.107 body weights showing that our method is sufficiently accurate to identify abnormalities in running technique among recreational runners.

Validation of a Reversible Lameness Model and the Assessment of a Topically Applied Nonsteroidal Anti-Inflammatory Drug

The objective of this study was to validate and use a model of reversible foot lameness in the horse. The model used both forelimb hooves fitted with a clamp. After force platform baseline measurements, one clamp was tightened to induce an asymmetry index (ASI) between 25% and 30% and left in place for 120 hours. Serial force platform measurements were obtained. After 120 hours, the clamp was released, and force platform data were recorded until the horse returned to soundness. The procedure was repeated on the opposite forelimb. To use the model, the same procedure was performed in another group of horses with one limb treated with topical diclofenac at 12-hour intervals beginning when the initial ASI was between 25% and 30% and continued for 120 hours. The response was evaluated for each outcome variable using linear mixed models. Time (duration of clamp being tight), limb (left or right), and clamping order (first or second foot) were fixed effects, whereas horse was a random effect. A similar analysis was completed with the additional variable (diclofenac treatment) for the model utilization data. For model validation, the only significant force plate data variable was time, which is consistent with model design. For model utilization, there was a significant effect of time and a significant decrease in the ASI associated with topical diclofenac. The model created a consistent lameness that will provide a mechanism to compare treatments for pain and lameness. Topical diclofenac applied twice daily decreased the lameness associated with the model.

Validation and comparison of shank and lumbar-worn IMUs for step time estimation.

Gait assessment is frequently used as an outcome measure to determine changes in an individual's mobility and disease processes. Inertial measurement units (IMUs) are quickly becoming commonplace in gait analysis. The purpose of this study was to determine and compare the validity of shank and lumbar IMU mounting locations in the estimation of temporal gait features. Thirty-seven adults performed 20 walking trials each over a gold standard force platform while wearing shank and lumbar-mounted IMUs. Data from the IMUs were used to estimate step times using previously published algorithms and were compared with those derived from the force platform. There was an excellent level of correlation between the force platform and shank (r=0.95) and lumbar-mounted (r=0.99) IMUs. Bland-Altman analysis demonstrated high levels of agreement between the IMU and the force platform step times. Confidence interval widths were 0.0782 s for the shank and 0.0367 s for the lumbar. Both IMU mounting locations provided accurate step time estimations, with the lumbar demonstrating a marginally superior level of agreement with the force platform. This validation indicates that the IMU system is capable of providing step time estimates within 2% of the gold standard force platform measurement.

Development of three-dimensional dynamic grinding force measurement platform

In order to accurately measure and control high-frequency grinding force in the process of grinding, a novel measurement method of three-dimensional grinding force with mutual perpendicular and independent elastic elements is proposed in this paper. To detect the high frequency grinding force, a resistance strain-type three-dimensional grinding force measurement platform was designed and developed. The key performance indicators of the measurement platform were investigated via finite element simulation. In addition, the detection performance of the measurement platform was researched and verified through natural frequency measurement experiments, static calibration experiments, and grinding experiments. The results show that the proposed method can effectively alleviate the inherent contradiction between natural frequency and sensitivity in the traditional dynamometer; the measurement platform as-established fully meets the performance requirements of three-dimensional dynamic grinding force detection. To this effect, the results discussed here provide technical support for achieving accurate detection of high frequency grinding force, monitoring grinding processes, optimizing grinding parameters, and improving grinding quality.

Postural Stability Assessment of University Marching Musicians Using Force Platform Measures.

Lower extremity injury is prevalent in marching musicians, and poor postural stability is a possible risk factor for this. The external load of an instrument may predispose these performers to injury by decreasing postural stability. The purpose of this study was to determine the relationship between instrument load and static and dynamic postural stability in this population. Fourteen university marching musicians were recruited and completed a balance assessment protocol on a force platform with and without their instrument. Mean center of pressure (CoP) displacement was then calculated for each exercise in the anterior/posterior and medial/lateral planes. Mean anterior/posterior CoP displacement significantly increased in the instrument condition for the static surface, eyes closed, 2 feet condition (p≤0.005; d=0.89). No significant differences were found in the medial/lateral plane between non-instrument and instrument conditions. Significant differences were not found between test stance conditions independent of group. Comparisons between the non-instrument-loaded and instrument-loaded conditions revealed possible significance of instrument load on postural stability in the anterior/posterior plane. Mean differences indicated that an unstable surface created a greater destabilizing effect on postural stability than instrument load.

Development and calibration of an air-floating six-axis force measurement platform using self-calibration

This paper describes the design, working principle, as well as calibration of an air-floating six-axis force measurement platform, where the floating plate and nozzles were connected without contact, preventing inter-dimensional coupling and increasing precision significantly. The measurement repeatability error of the force size in the platform is less than 0.2% full scale (FS), which is significantly better than the precision of 1% FS in the six-axis force sensors on the current market. We overcame the difficulties of weight loading device in high-precision calibration by proposing a self-calibration method based on the floating plate gravity and met the calibration precision requirement of 0.02% FS. This study has general implications for the development and calibration of high-precision multi-axis force sensors. In particular, the air-floating six-axis force measurement platform could be applied to the calibration of some special sensors such as flexible tactile sensors and may be used as a micro-nano mechanical assembly platform for real-time assembly force testing.

Reliability and Validity of Force Platform Measures of Balance Impairment in Individuals With Parkinson Disease.

Complex movement and balance impairments in people with Parkinson disease (PD) contribute to high fall risk. Comprehensive balance assessment is warranted to identify intrinsic fall risk factors and direct interventions. The purpose of this study was to examine the psychometric properties of 3 balance measures of a force platform (FP) system in people with PD. Forty-two community-dwelling individuals with idiopathic PD completed the testing protocol. Test-retest reliability was assessed for the Limits of Stability Test (LOS), Motor Control Test (MCT), and Sensory Organization Test (SOT). Intraclass correlation coefficients (ICC [2,1]) were calculated to determine test-retest reliability and minimal detectable change. Validity was assessed by comparing the FP measures with criterion gait and balance measures using Pearson product moment correlations. Multiple regression analyses examined the contribution of PD characteristics to FP measures. All primary FP variables demonstrated excellent test-retest reliability (ICC=.78-.92). The SOT and LOS demonstrated fair to good correlations with criterion measures, whereas the MCT had fair correlations to balance measures only. Both SOT composite equilibrium and MCT average latency were moderately associated with disease severity. This study's sample had a relatively small number of participants with a positive fall history, which may limit the generalizability of the findings. This study's findings provide support that FP measures are reliable and valid tests of balance impairment in people with PD. Disease severity was significantly associated with SOT and MCT measures, perhaps reflecting that these tests are meaningful indicators of decline in postural control with disease progression. Force platform measures may provide valuable quantitative information about underlying balance impairments in people with PD to guide therapeutic interventions for fall risk reduction.

Reductions in knee joint forces with weight loss are attenuated by gait adaptations in class III obesity

A consensus exists that high knee joint forces are a precursor to knee osteoarthritis and weight loss reduces these forces. Because large weight loss also leads to increased step length and walking velocity, knee contact forces may be reduced less than predicted by the magnitude of weight loss. The purpose was to determine the effects of weight loss on knee muscle and joint loads during walking in Class III obese adults. We determined through motion capture, force platform measures and biomechanical modeling the effects of weight loss produced by gastric bypass surgery over one year on knee muscle and joint loads during walking at a standard, controlled velocity and at self-selected walking velocities. Weight loss equaling 412N or 34% of initial body weight reduced maximum knee compressive force by 824N or 67% of initial body weight when walking at the controlled velocity. These changes represent a 2:1 reduction in knee force relative to weight loss when walking velocity is constrained to the baseline value. However, behavioral adaptations including increased stride length and walking velocity in the self-selected velocity condition attenuated this effect by ∼50% leading to a 392N or 32% initial body weight reduction in compressive force in the knee joint. Thus, unconstrained walking elicited approximately 1:1 ratio of reduction in knee force relative to weight loss and is more indicative of walking behavior than the standard velocity condition. In conclusion, massive weight loss produces dramatic reductions in knee forces during walking but when patients stride out and walk faster, these favorable reductions become substantially attenuated.

The contribution of postural balance analysis in older adult fallers: A narrative review

Falls are a serious health problem for older adults. Several studies have identified the decline of postural balance as one of the main risk factors for falls. Contrary to what may be believed, the capability of force platform measurements to predict falls remains uncertain. The focus of this narrative review is the identification of postural characteristics of older adults at risk of falling using both static and dynamic postural balance assessments. The literature analysis was conducted on Medline/PubMed. The search ended in May 2015. Centre of pressure (CoP) path length, CoP velocity and sway in medial lateral and anterior-posterior are the variables that distinguish older adult fallers from non-fallers. Recommendations to medical personnel on how to provide efficient balance training for older adults are offered, discussing the relevance and limitations of postural stability on static and dynamic board in falling risk prevention.

Investigation of relationship between interfacial electroadhesive force and surface texture

A novel investigation into the relationship between the obtainable interfacial electroadhesive forces and different surface textures is presented in this paper. Different surface textures were generated then characterized based on a recognized areal-based non-contact surface texture measurement platform and procedure. An advanced electroadhesive force measurement platform and procedure were then implemented to measure the obtainable electroadhesive forces on those different surface textures. The results show that the obtained interfacial electroadhesive forces increase with decreasing Sq (root mean square height) value of the substrate surface provided that the difference in Sq between the different substrates is over 5 μm. Also, the higher the applied voltage, the larger the relative increase in electroadhesive forces observed. However, when the difference of Sq value between different substrate surfaces is below 2 μm, the obtained interfacial electroadhesive forces do not necessarily increase with decreasing Sq. Furthermore, the obtainable electroadhesive forces are not necessarily the same when the Sq value of two substrate surfaces are the same due to the fact that the direction of the surface texture plays an important role in achieving electroadhesive forces.

Agreement of spatio-temporal gait parameters between a vertical ground reaction force decomposition algorithm and a motion capture system

IntroductionA ground reaction force decomposition algorithm based on large force platform measurements has recently been developed to analyze ground reaction forces under each foot during the double support phase of gait. However, its accuracy for the measurement of the spatiotemporal gait parameters remains to be established. ObjectiveThe aim of the present study was to establish the agreement between the spatiotemporal gait parameters obtained using (1) a walkway (composed of six large force platforms) and the newly developed algorithm, and (2) an optoelectronic motion capture system. MethodsTwenty healthy children and adolescents (age range: 6–17 years) and 19 healthy adults (age range: 19–51 years) participated in this study. They were asked to walk at their preferred speed and at a speed that was faster than the preferred one. Each participant performed three blocks of three trials in each of the two walking speed conditions. ResultsThe spatiotemporal gait parameters measured with the algorithm did not differ by more than 2.5% from those obtained with the motion capture system. The limits of agreement represented between 3% and 8% of the average spatiotemporal gait parameters. Repeatability of the algorithm was slightly higher than that of the motion capture system as the coefficient of variations ranged from 2.5% to 6%, and from 1.5% to 3.5% for the algorithm and the motion capture system, respectively. ConclusionThe proposed algorithm provides valid and repeatable spatiotemporal gait parameter measurements and offers a promising tool for clinical gait analysis. Further studies are warranted to test the algorithm in people with impaired gait.

Design and Development of Optical Sensor Based Ground Reaction Force Measurement Platform for GAIT and Geriatric Studies

This paper describes an ab-initio design, development and calibration results of an Optical Sensor Ground Reaction Force Measurement Platform (OSGRFP) for gait and geriatric studies. The developed system employs an array of FBG sensors to measure the respective ground reaction forces from all three axes (X, Y and Z), which are perpendicular to each other. The novelty of this work is two folded. One is in its uniqueness to resolve the tri axial resultant forces during the stance in to the respective pure axis loads and the other is the applicability of inherently advantageous FBG sensors which are most suitable for biomechanical instrumentation. To validate the response of the FBG sensors installed in OSGRFP and to measure the cross sensitivity of the force applied in other directions, load sensors with indicators are used. Further in this work, relevant mathematical formulations are presented for extracting respective ground reaction forces from wavelength shifts/strain of FBG sensors on the OSGRFP. The result of this device has implications in understanding the foot function, identifying issues in gait cycle and measuring discrepancies between left and right foot. The device also provides a method to quantify and compare relative postural stability of different subjects under test, which has implications in post-surgical rehabilitation, geriatrics and optimizing training protocols for sports personnel.

A flexible tactile sensor calibration method based on an air-bearing six-dimensional force measurement platform.

A number of common issues related to the process of flexible tactile sensor calibration are discussed in this paper, and an estimate of the accuracy of classical calibration methods, as represented by a weight-pulley device, is presented. A flexible tactile sensor calibration method that is based on a six-dimensional force measurement is proposed on the basis of a theoretical analysis. A high-accuracy flexible tactile sensor calibration bench based on the air-bearing six-dimensional force measurement principle was developed to achieve a technically challenging measurement accuracy of 2% full scale (FS) for three-dimensional (3D) flexible tactile sensor calibration. The experimental results demonstrate that the accuracy of the air-bearing six-dimensional force measurement platform can reach 0.2% FS. Thus, the system satisfies the 3D flexible tactile sensor calibration requirement of 2% FS.

Behavior of medial gastrocnemius motor units during postural reactions to external perturbations after stroke

ObjectiveThis study investigated the behavior of medial gastrocnemius (GM) motor units (MU) during external perturbations in standing in people with chronic stroke. MethodsGM MUs were recorded in standing while anteriorly-directed perturbations were introduced by applying loads of 1% body mass (BM) at the pelvis every 25–40s until 5% BM was maintained. Joint kinematics, surface electromyography (EMG), and force platform measurements were assessed. ResultsAlthough external loads caused a forward progression of the anterior–posterior centre of pressure (APCOP), people with stroke decreased APCOP velocity and centre of mass (COM) velocity immediately following the highest perturbations, thereby limiting movement velocity in response to perturbations. MU firing rate did not increase with loading but the GM EMG magnitude increased, reflecting MU recruitment. MU inter spike interval (ISI) during the dynamic response was negatively correlated with COM velocity and hip angular velocity. ConclusionsThe GM utilized primarily MU recruitment to maintain standing during external perturbations. The lack of MU firing rate modulation occurred with a change in postural central set. However, the relationship of MU firing rate with kinematic variables suggests underlying long-loop responses may be somewhat intact after stroke. SignificancePeople with stroke demonstrate alterations in postural control strategies which may explain MU behavior with external perturbations.