Estimation of tri-axial walking ground reaction forces of left and right foot from total forces in real-life environments

This is the final version of the article. Available from MDPI via the DOI in this record.Continuous monitoring of natural human gait in real-life environments is essential in many applications including disease monitoring, rehabilitation, and professional sports. Wearable inertial measurement units are successfully used to measure body kinematics in real-life environments and to estimate total walking ground reaction forces GRF(t) using equations of motion. However, for inverse dynamics and clinical gait analysis, the GRF(t) of each foot is required separately. Using an experimental dataset of 1243 tri-axial separate-foot GRF(t) time histories measured by the authors across eight years, this study proposes the ‘Twin Polynomial Method’ (TPM) to estimate the tri-axial left and right foot GRF(t) signals from the total GRF(t) signals. For each gait cycle, TPM fits polynomials of degree five, eight, and nine to the known single-support part of the left and right foot vertical, anterior-posterior, and medial-lateral GRF(t) signals, respectively, to extrapolate the unknown double-support parts of the corresponding GRF(t) signals. Validation of the proposed method both with force plate measurements (gold standard) in the laboratory, and in real-life environment showed a peak-to-peak normalized root mean square error of less than 2.5%, 6.5% and 7.5% for the estimated GRF(t) signals in the vertical, anterior-posterior and medial-lateral directions, respectively. These values show considerable improvement compared with the currently available GRF(t) decomposition methods in the literature.The authors acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) for the following research grants: Frontier Engineering Grant EP/K03877X/1 (Modelling complex and partially identified engineering problems: Application to the individualized multiscale simulation of the musculoskeletal system); and Platform Grant EP/G061130/2 (Dynamic performance of large civil engineering structures: an integrated approach to management, design and assessment)

Human-Structure Dynamic Interaction during Short-Distance Free Falls

The dynamic interactions of falling human bodies with civil structures, regardless of their potentially critical effects, have sparsely been researched in contact biomechanics. The physical contact models suggested in the existing literature, particularly for short-distant falls in home settings, assume the human body falls on a “rigid” (not vibrating) ground. A similar assumption is usually made during laboratory-based fall tests, including force platforms. Based on observations from a set of pediatric head-first free fall tests, the present paper shows that the dynamics of the grounded force plate are not always negligible when doing fall test in a laboratory setting. By using a similar analogy for lightweight floor structures, it is shown that ignoring the dynamics of floors in the contact model can result in an up to 35% overestimation of the peak force experienced by a falling human. A nonlinear contact model is suggested, featuring an agent-based modelling approach, where the dynamics of the falling human and the impact object (force plate or a floor structure here) are each modelled using a single-degree-of-freedom model to simulate their dynamic interactions. The findings of this research can have wide applications in areas such as impact biomechanics and sports science

Interaction between Walking Humans and Structures in Vertical Direction: A Literature Review

Realistic simulation of the dynamic effects of walking pedestrians on structures is still a considerable challenge. This is mainly due to the inter- and intra-subject variability of humans and their bodies and difficult-to-predict loading scenarios, including multipedestrian walking traffic and unknown human-structure interaction (HSI) mechanisms. Over the past three decades, several attempts have been made to simulate walking HSI in the lateral direction. However, research into the mechanisms of this interaction in the vertical direction, despite its higher likelihood and critical importance, is fragmented and incoherent. It is, therefore, difficult to apply and codify. This paper critically reviews the efforts to date to simulate walking HSI in the vertical direction, and highlights the key areas that need further investigation.The authors acknowledge the financial support, which came from the University of Sheffield doctoral scholarship for Dr Shahabpoor and the UK Engineering and Physical Sciences Research Council (EPSRC) for the following research grants: • Platform Grant EP/G061130/2 (Dynamic performance of large civil engineering structures: an integrated approach to management, design and assessment), • Standard Grant EP/I029567/1 (Synchronisation in dynamic loading due to multiple pedestrians and occupants of vibration-sensitive structures). And • Frontier Engineering Grant EP/K03877X/1 (Modelling complex and partially identified engineering problems: Application to the individualised multiscale simulation of the musculoskeletal system)

Interaction between Walking Humans and Structures in Vertical Direction: A Literature Review

Realistic simulation of the dynamic effects of walking pedestrians on structures is still a considerable challenge. This is mainly due to the inter- and intrasubject variability of humans and their bodies and difficult-to-predict loading scenarios, including multipedestrian walking traffic and unknown human-structure interaction (HSI) mechanisms. Over the past three decades, several attempts have been made to simulate walking HSI in the lateral direction. However, research into the mechanisms of this interaction in the vertical direction, despite its higher likelihood and critical importance, is fragmented and incoherent. It is, therefore, difficult to apply and codify. This paper critically reviews the efforts to date to simulate walking HSI in the vertical direction and highlights the key areas that need further investigation

Dynamic Interaction of Walking Humans with Pedestrian Structures in Vertical Direction Experimentally Based Probabilistic Modelling

There is a lack of credible and usable knowledge, specifically related to human-structure interaction in the vertical direction despite of its importance and potentially huge economic impact. The research presented in this thesis addresses this problem via a systematic combined experimental and analytical study of the effects of people on dynamic properties of vibrating structures they excite by walking. Series of extensive frequency response function based modal tests were performed on a full-scale test structure with more than one hundred test subjects walking in different loading scenarios. The experimental results were then used to identify the parameters of a single-degree-of-freedom (SDOF) mass-spring-damper (MSD) model of a walking human. Four different approaches, including agent-based modelling, were used to simulate measured scenarios of multi-pedestrian traffic. It was found that normal distributions with μ=2.864 Hz and σ= 0.191 Hz, and μ=0.295 and σ= 0.023 can describe the natural frequency and damping ratio of the SDOF MSD model of a walking human, respectively, when total mass of the human body is assumed as the mass of the SDOF system. A new vibration serviceability assessment method was proposed that takes into account not only the variability of the human body MSD parameters and the forcing function but also their interaction with the structure. Application of this novel method on two full-scale structures under walking traffic load verified its excellent performance yielding a maximum 10% error in estimating the level of structural response compared to 200-500% error margins when key design guidelines currently used around the world were employed. This method is versatile and, being easy to apply in practice, has the potential to replace the existing methods for simulating single and multi-pedestrian traffic on footbridges and floors

Effect of group walking traffic on dynamic properties of pedestrian structures

The increasing number of reported vibration serviceability problems in newly built pedestrian structures, such as footbridges and floors, under walking load has attracted considerable attention in the civil engineering community over the past two decades. The key design challenges are: the inter- and intra-subject variability of walking people, the unknown mechanisms of their interaction with the vibrating walking surfaces and the synchronisation between individuals in a group. Ignoring all or some of these factors makes the current design methods an inconsistent approximation of reality. This often leads to considerable over- or under-estimation of the structural response, yielding an unreliable assessment of vibration performance. Changes to the dynamic properties of an empty structure due to the presence of stationary people have been studied extensively over the past two decades. The understanding of the similar effect of walking people on laterally swaying bridges has improved tremendously in the past decade, due to considerable research prompted by the Millennium Bridge problem. However, there is currently a gap in knowledge about how moving pedestrians affect the dynamic properties of vertically vibrating structures. The key reason for this gap is the scarcity of credible experimental data pertinent to moving pedestrians on vertically vibrating structures, especially for multi-pedestrian traffic. This paper addresses this problem by studying the dynamic properties of the combined human-structure system, i.e. occupied structure damping ratio, natural frequency and modal mass. This was achieved using a comprehensive set of frequency response function records, measured on a full-scale test structure, which was occupied by various numbers of moving pedestrians under different walking scenarios. Contrary to expectations, it was found that the natural frequency of the joint moving human-structure system was higher than that of the empty structure, while it was lower when the same people were standing still. The damping ratio of the joint human-structure system was considerably higher than that of the empty structure for both the walking and standing people – in agreement with previous reports for stationary people - and was more prominent for larger groups. Interestingly, it was found that the walking human-structure system has more damping compared with the equivalent standing human-structure system. The properties of a single degree of freedom mass-spring-damper system representing a moving crowd needed to replicate these observations have been identified

VSimulators:A New UK-based Immersive Experimental Facility for Studying Occupant Response to Wind-induced Motion of Tall Buildings

Current vibration serviceability assessment criteria for wind-induced vibrationsin tall buildings are based largely on human ‘perception’ thresholds which is shown not to be directly translatable to human ‘acceptability’ of vibrations. There is also a considerable debate about both the metrics and criteria for vibration acceptability, such as frequency of occurrence or peak vs mean vibration, and how these might vary with the nature of the vibration. Furthermore, the design criteria are necessarily simplified for ease of application so cannot account for a range of environmental, situational and human factors that may enhance or diminish the impact of vibrations on serviceability. The dual-site VSimulatorsfacility was created specifically to provide an experimental platform to address gaps in understanding of human response to building vibration. This paper considers how VSimulators can be used to inform general design guidance and support design of specific buildings for habitability, in terms of vibration, which allow engineers and clients to make informed decisions with regard to sustainable design, in terms of energy and financial cost. This paper first provides a brief overview of current vibration serviceability assessment guidelines, and the current understanding and limitations of occupants’ acceptability of wind-induced motion in tall buildings. It then describes how the dual-site VSimulators facility at the Universities of Bath and Exeter can be used to assess the effects of motion and environment on human comfort, wellbeing and productivity with examples of how the facility capabilities have been used to provide new, human experience based experimental research approaches

Estimation of vertical walking ground reaction force in real-life environments using single IMU sensor

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordMonitoring natural human gait in real-life environments is essential in many applications, including quantification of disease progression, monitoring the effects of treatment, and monitoring alteration of performance biomarkers in professional sports. Nevertheless, developing reliable and practical techniques and technologies necessary for continuous real-life monitoring of gait is still an open challenge. A systematic review of English-language articles from scientific databases including Scopus, ScienceDirect, Pubmed, IEEE Xplore, EBSCO and MEDLINE were carried out to analyse the ‘accuracy’ and ‘practicality’ of the current techniques and technologies for quantitative measurement of the tri-axial walking ground reactions outside the laboratory environment, and to highlight their strengths and shortcomings. In total, 679 relevant abstracts were identified, 54 full-text papers were included in the paper and the quantitative results of 17 papers were used for meta-analysis and comparison. Three classes of methods were reviewed: (1) methods based on measured kinematic data; (2) methods based on measured plantar pressure; and (3) methods based on direct measurement of ground reactions. It was found that all three classes of methods have competitive accuracy levels with methods based on direct measurement of the ground reactions showing highest accuracy while being least practical for long-term real-life measurement. On the other hand, methods that estimate ground reactions using measured body kinematics show highest practicality of the three classes of methods reviewed. Among the most prominent technical and technological challenges are: (1) reducing the size and price of tri-axial load-cells; (2) improving the accuracy of orientation measurement using IMUs; (3) minimizing the number and optimizing the location of required IMUs for kinematic measurement; (4) increasing the durability of pressure insole sensors, and (5) enhancing the robustness and versatility of the ground reactions estimation methods to include pathological gaits and natural variability of gait in real-life physical environment.The authors acknowledge the financial support provided by the UK Engineering and Physical Sciences Research Council (EPSRC) for the following research grants: Frontier Engineering Grant EP/K03877X/1 (Modelling complex and partially identified engineering problems: Application to the individualized multi-scale simulation of the musculoskeletal system); and Platform Grant EP/G061130/2 (Dynamic performance of large civil engineering structures: an integrated approach to management, design and assessment)

Using inertial measurement units to identify medio-lateral ground reaction forces due to walking and swaying

Horizontal ground reaction forces (GRFs) due to human walking and swaying have been investigated (respectively) through direct measurements using a treadmill and a set of force plates. These GRFs have also been measured (or estimated) indirectly using acceleration data provided by inertial measurement units (IMUs). One motivation for this research has been the lack of published data on these two forms of loading that are generated by movements of the human body in the medio-lateral plane perpendicular to the direction of walking or the direction faced during swaying. The other motivation, following from successful developments in applying IMUs to in-situ vertical GRF measurements, has been to identify best practice for estimating medio-lateral GRFs outside the constraints of a laboratory. Examination of 852 treadmill measurements shows that medio-lateral GRFs at the first sub-harmonic of pacing rate can exceed 10% of body weight. Using a smaller and more recent set of measurements including motion capture, it has been shown that IMUs can be used to reconstruct these GRFs using a linear combination of body accelerations at each of the lower back and sternum positions. There are a number of potential applications for this capability yet to be explored, in particular relating to footbridge performance. A separate set of measurements using force plates has shown that harmonic components of medio-lateral dynamic load factors due to on the spot swaying can approach 50% of body weight. Such forces provide a capability to excite horizontal vibration modes of large civil structures with frequencies below 2 Hz that are problematic for mechanical excitation. As with walking, the ability to use IMUs to estimate medio-lateral swaying GRFs outside laboratory constraints has been demonstrated. As for walking a pair of IMUs is needed, but the best linear combination varies strongly between individuals, according to swaying style. In-situ application of indirect measurement has been successfully demonstrated through a very challenging application of system identification of a multi-storey building, including estimation of modal mass.</p

Real-life measurement of tri-axial walking ground reaction forces using optimal network of wearable inertial measurement units

Monitoring natural human gait in real-life environment is essential in many applications including quantification of disease progression, and monitoring the effects of treatment and alteration of performance biomarkers in professional sports. Nevertheless, reliable and practical techniques and technologies necessary for continuous real-life monitoring of gait is still not available. This paper explores in detail the correlations between the acceleration of different body segments and walking ground reaction forces GRF( t )in three dimensions and proposes three sensory systems, with one, two and three inertial measurement units (IMUs), to estimate GRF( t )in the vertical (V), medial-lateral (ML) and anterior-posterior (AP) directions. The NARMAX non-linear system identification method was utilized to identify the optimal location for IMUs on the body for each system. A simple linear model was then proposed to estimate GRF( t )based on the correlation of segmental accelerations with each other. It was found that, for the three-IMU system, the proposed model estimatedGRF( t )with average peak-to-peak normalized root mean square error (NRMSE) of 7%, 16% and 18% in V, AP and ML directions, respectively. With a simple subject-specific training at the beginning, these errors were reduced to 7%, 13% and 13% in V, AP and ML directions, respectively. These results were found favorably comparable with the results of the benchmark NARMAX model, with subject-specific training, with 0% (V), 4% (AP) and 1% (ML) NRMSE difference