A physiology-based inverse dynamic analysis of human gait using sequential convex programming: a comparative study

This paper presents an enhanced version of the previously proposed physiological inverse approach (PIA) to calculate musculotendon (MT) forces and evaluates the proposed methodology in a comparative study. PIA combines an inverse dynamic analysis with an optimisation approach that imposes muscle physiology and optimises performance over the entire motion. To solve the resulting large-scale, nonlinear optimisation problem, we neglected muscle fibre contraction speed and an approximate quadratic optimisation problem (PIA-QP) was formulated. Conversely, the enhanced version of PIA proposed in this paper takes into account muscle fibre contraction speed. The optimisation problem is solved using a sequential convex programing procedure (PIA-SCP). The comparative study includes PIA-SCP, PIA-QP and two commonly used approaches from the literature: static optimisation (SO) and computed muscle control (CMC). SO and CMC make simplifying assumptions to limit the computational time. Both methods minimise an instantaneous performance criterion. Furthermore, SO does not impose muscle physiology. All methods are applied to a gait cycle of six control subjects. The relative root mean square error averaged over all subjects, ε(RMS), between the joint torques simulated from the optimised activations and the joint torques obtained from the inverse dynamic analysis was about twice as large for SO (ε(RMS) = 86) as compared with CMC (ε(RMS) = 39) and PIA-SCP (ε(RMS) = 50). ε(RMS) was at least twice as large for PIA-QP (ε(RMS) = 197) than for all other methods. As compared with CMC, muscle activation patterns predicted by PIA-SCP better agree with experimental electromyography (EMG). This study shows that imposing muscle physiology as well as globally optimising performance is important to accurately calculate MT forces underlying gait.     

A computational model for dynamic analysis of the human gait

Biomechanical models are important tools in the study of human motion. This work proposes a computational model to analyse the dynamics of lower limb motion using a kinematic chain to represent the body segments and rotational joints linked by viscoelastic elements. The model uses anthropometric parameters, ground reaction forces and joint Cardan angles from subjects to analyse lower limb motion during the gait. The model allows evaluating these data in each body plane. Six healthy subjects walked on a treadmill to record the kinematic and kinetic data. In addition, anthropometric parameters were recorded to construct the model. The viscoelastic parameter values were fitted for the model joints (hip, knee and ankle). The proposed model demonstrated that manipulating the viscoelastic parameters between the body segments could fit the amplitudes and frequencies of motion. The data collected in this work have viscoelastic parameter values that follow a normal distribution, indicating that these values are directly related to the gait pattern. To validate the model, we used the values of the joint angles to perform a comparison between the model results and previously published data. The model results show a same pattern and range of values found in the literature for the human gait motion.     

Effect of body weight support variation on muscle activities during robot assisted gait: a dynamic simulation study

Background and Objectives: While body weight support (BWS) intonation is vital during conventional gait training of neurologically challenged subjects, it is important to evaluate its effect during robot assisted gait training. In the present research we have studied the effect of BWS intonation on muscle activities during robotic gait training using dynamic simulations. Methods: Two dimensional (2-D) musculoskeletal model of human gait was developed conjointly with another 2-D model of a robotic orthosis capable of actuating hip, knee and ankle joints simultaneously. The musculoskeletal model consists of eight major muscle groups namely; soleus (SOL), gastrocnemius (GAS), tibialis anterior (TA), hamstrings (HAM), vasti (VAS), gluteus maximus (GLU), uniarticular hip flexors (iliopsoas, IP), and Rectus Femoris (RF). BWS was provided at levels of 0, 20, 40 and 60% during the simulations. In order to obtain a feasible set of muscle activities during subsequent gait cycles, an inverse dynamics algorithm along with a quadratic minimization algorithm was implemented. Results: The dynamic parameters of the robot assisted human gait such as joint angle trajectories, ground contact force (GCF), human limb joint torques and robot induced torques at different levels of BWS were derived. The patterns of muscle activities at variable BWS were derived and analysed. For most part of the gait cycle (GC) the muscle activation patterns are quite similar for all levels of BWS as is apparent from the mean of muscle activities for the complete GC. Conclusions: Effect of BWS variation during robot assisted gait on muscle activities was studied by developing dynamic simulation. It is expected that the proposed dynamic simulation approach will provide important inferences and information about the muscle function variations consequent upon a change in BWS during robot assisted gait. This information shall be quite important while investigating the influence of BWS intonation on neuromuscular parameters of interest during robotic gait training.     

A novel method to evaluate error in anatomical marker placement using a modified generalized Procrustes analysis

As biomechanical research evolves, a continuing challenge is the standardization of data collection and analysis techniques. In gait analysis, placement of markers to construct an anatomical model has been identified as the single greatest source of error; however, there is currently no standardized approach to quantifying these errors. The current study applies morphometric methods, including a generalized Procrustes analysis (GPA) and a nearest neighbour comparison to quantify discrepancies in marker placement, with the goal of improving reliability in gait analysis. An extensive data-set collected by an Expert (n = 340) was used to evaluate marker placements performed by a Novice (n = 55). Variances identified through principal component analysis were used to create a modified GPA to transform anatomical data, and scaled coordinates from the Novice data-set were then scored against the Expert subset. The results showed quantitative differences in marker placement, suggesting that, although training improved consistency, systematic biases remained.     

A comparative study of muscle force estimates using Huxley's and Hill's muscle model

Determination of muscle forces in individual muscles is often essential to assess optimal performance of human motion. Inverse dynamic methods based on the kinematics of the given motion and on the use of optimisation approach are the most widely used for muscle force estimation. The aim of this study was to estimate how the choice of muscle model influences predicted muscle forces. Huxley's (1957, Prog Biophys Biop Chem. 7: 255–318) and Hill's (1938, Proc R Soc B. 126: 136–195) muscle models were used for determination of muscle forces of two antagonistic muscles of the lower extremity during cycling. Huxley's model is a complex model that couples biochemical and physical processes with the microstructure of the muscle whereas the Hill's model is a phenomenological model. Muscle forces predicted by both models are within the same range. Huxley's model predicts more realistic patterns of muscle activation but it is computationally more demanding. Therefore, if the overall muscle forces are to be assessed, it is reasonable to use a simpler implementation based on Hill's model.     

Estimation of muscle forces in gait using a simulation of the electromyographic activity and numerical optimization

Clinical gait analysis provides great contributions to the understanding of gait patterns. However, a complete distribution of muscle forces throughout the gait cycle is a current challenge for many researchers. Two techniques are often used to estimate muscle forces: inverse dynamics with static optimization and computer muscle control that uses forward dynamics to minimize tracking. The first method often involves limitations due to changing muscle dynamics and possible signal artefacts that depend on day-to-day variation in the position of electromyographic (EMG) electrodes. Nevertheless, in clinical gait analysis, the method of inverse dynamics is a fundamental and commonly used computational procedure to calculate the force and torque reactions at various body joints. Our aim was to develop a generic musculoskeletal model that could be able to be applied in the clinical setting. The musculoskeletal model of the lower limb presents a simulation for the EMG data to address the common limitations of these techniques. This model presents a new point of view from the inverse dynamics used on clinical gait analysis, including the EMG information, and shows a similar performance to another model available in the OpenSim software. The main problem of these methods to achieve a correct muscle coordination is the lack of complete EMG data for all muscles modelled. We present a technique that simulates the EMG activity and presents a good correlation with the muscle forces throughout the gait cycle. Also, this method showed great similarities whit the real EMG data recorded from the subjects doing the same movement.     

A comparative collision-based analysis of human gait

This study compares human walking and running, and places them within the context of other mammalian gaits. We use a collision-based approach to analyse the fundamental dynamics of the centre of mass (CoM) according to three angles derived from the instantaneous force and velocity vectors. These dimensionless angles permit comparisons across gait, species and size. The collision angle Φ, which is equivalent to the dimensionless mechanical cost of transport CoT_mech, is found to be three times greater during running than walking of humans. This threefold difference is consistent with previous studies of walking versus trotting of quadrupeds, albeit tends to be greater in the gaits of humans and hopping bipeds than in quadrupeds. Plotting the collision angle Φ together with the angles of the CoM force vector Θ and velocity vector Λ results in the functional grouping of bipedal and quadrupedal gaits according to their CoM dynamics—walking, galloping and ambling are distinguished as separate gaits that employ collision reduction, whereas trotting, running and hopping employ little collision reduction and represent more of a continuum that is influenced by dimensionless speed. Comparable with quadrupedal mammals, collision fraction (the ratio of actual to potential collision) is 0.51 during walking and 0.89 during running, indicating substantial collision reduction during walking, but not running, of humans.     

A study of gait acceleration and synchronisation in healthy adult subjects

Accelerometry-based gait analysis is widely recognised as a promising tool in healthcare and clinical settings since it is unobtrusive, inexpensive and capable of providing insightful information on human gait characteristics. In order to expand the application of this technology in daily environments, it is desirable to develop reliable gait measures and their extraction methods from the acceleration signal that can differentiate between normal and atypical gait. Important examples of such measures are gait cycle and gait-induced acceleration magnitude, which are known to be closely related to each other depending on each individual's physical condition. In this study, we derive a model equation with two parameters which captures the essential relationships between gait cycle and gait acceleration based on experiments and physical modelling. We also introduce as a new gait parameter a set of indexes to evaluate the synchronisation behaviour of gait timing. The function and utility of the proposed parameters are examined in 11 healthy subjects during walking under various selected conditions.     

A preliminary study of modification of gait in real-time using surface electromyography

Modification of abnormal gait was attempted in real-time using a surface electromyography-based protocol to teach recruitment of the anterior tibialis at the correct time in the gait cycle. Two children diagnosed with cerebral palsy were able to learn volitional control of the anterior tibialis as demonstrated by improved clearance of the toe on the swing phase of the gait and newly learned ability to recruit and relax the anterior tibialis. The children were able to walk with the new gait pattern and reproduce the old one at will. Implications for future research in this area are discussed.     

行走模式对人体下肢三维步态、肌电信号的影响

目的:揭示人体在主动和被动两种行走模式下的步态特征与下肢主要肌群的肌电信号变化规律。方法:选取12名在校男大学生,通过Greenjog履带式自发力跑台和h/p/cosmos电动跑台建立主动式和被动式行走模型,先后在两种模式下以3种递增速度即慢速(2 km/h)、常速(4 km/h)、和快速(6 km/h)进行一次性步行运动,运用三维运动捕捉分析系统和表面肌电测试仪,分别对每种速度采集2 min的连续三维步态和肌电信号数据。结果:慢速时,被动式行走的支撑相占比显著高于主动式行走(P<0.05),而摆动相占比和膝关节角度变化值则显著低于主动式行走(P<0.05);常速时,被动式行走的膝关节角度变化值和股二头肌积分肌电值显著低于主动式行走(P<0.05);快速时,被动式行走的膝关节、踝关节角度变化值和股二头肌积分肌电值显著低于主动式行走(P<0.01);此外,随着步行速度的增加,被动式行走的胫骨前肌积分肌电值呈现显著增高的趋势(P<0.05)。结论:随着步行速度的增加,人体主动步行时的膝关节活动范围更充分,对主动肌的锻炼作用更明显。     

The development and concurrent validity of a real-time algorithm for temporal gait analysis using inertial measurement units

The use of inertial measurement units (IMUs) for gait analysis has emerged as a tool for clinical applications. Shank gyroscope signals have been utilized to identify heel-strike and toe-off, which serve as the foundation for calculating temporal parameters of gait such as single and double limb support time. Recent publications have shown that toe-off occurs later than predicted by the dual minima method (DMM), which has been adopted as an IMU-based gait event detection algorithm. In this study, a real-time algorithm, Noise-Zero Crossing (NZC), was developed to accurately compute temporal gait parameters. Our objective was to determine the concurrent validity of temporal gait parameters derived from the NZC algorithm against parameters measured by an instrumented walkway. The accuracy and precision of temporal gait parameters derived using NZC were compared to those derived using the DMM. The results from Bland-Altman Analysis showed that the NZC algorithm had excellent agreement with the instrumented walkway for identifying the temporal gait parameters of Gait Cycle Time (GCT), Single Limb Support (SLS) time, and Double Limb Support (DLS) time. By utilizing the moment of zero shank angular velocity to identify toe-off, the NZC algorithm performed better than the DMM algorithm in measuring SLS and DLS times. Utilizing the NZC algorithm’s gait event detection preserves DLS time, which has significant clinical implications for pathologic gait assessment.     

Custom sizing of lower limb exoskeleton actuators using gait dynamic modelling of children with cerebral palsy

The use of exoskeletons as an aid for people with musculoskeletal disorder is the subject to an increasing interest in the research community. These devices are expected to meet the specific needs of users, such as children with cerebral palsy (CP) who are considered a significant population in pediatric rehabilitation. Although these exoskeletons should be designed to ease the movement of people with physical shortcoming, their design is generally based on data obtained from healthy adults, which leads to oversized components that are inadequate to the targeted users. Consequently, the objective of this study is to custom-size the lower limb exoskeleton actuators based on dynamic modeling of the human body for children with CP on the basis of hip, knee, and ankle joint kinematics and dynamics of human body during gait. For this purpose, a multibody modeling of the human body of 3 typically developed children (TD) and 3 children with CP is used. The results show significant differences in gait patterns especially in knee and ankle with respectively 0.39 and ?0.33 (Nm/kg) maximum torque differences between TD children and children with CP. This study provides the recommendations to support the design of actuators to normalize the movement of children with CP.     

Influence of plantar cutaneous sensitivity on daily fluctuations of postural control and gait in institutionalized older adults: a hierarchical cluster analysis

The aim of this study was to characterize daily fluctuations in postural control, gait and plantar cutaneous sensitivity in institutionalized older adults. Twenty-five older adults (>85 years old) living in a nursing home were recruited. Postural, gait and plantar cutaneous sensitivity parameters were collected at the following times: 8:00, 11:00, 14:00 and 17:00. Statistics were first calculated with the data from the whole group of the participants. A hierarchical cluster analysis was performed as a second step in order to determine if there was more than one pattern in the daily fluctuations of gait, postural control and plantar cutaneous sensitivity. When considering data from the whole group, results showed that postural control deteriorated from morning to the early afternoon and that gait improved from early to late morning. Daily fluctuations of plantar cutaneous sensitivity showed a decrease in tactile acuity in the afternoon. For most gait, postural control and plantar cutaneous sensitivity parameters, the hierarchical cluster analysis showed that there were three subgroups within the whole group of participants who had similar fluctuation patterns. Participants with the best tactile acuity, postural control and gait displayed relatively constant patterns without a period of increased risk of falling. By contrast, participants who presented a poor tactile acuity with a less efficient postural control and gait had greater daily fluctuations of plantar cutaneous sensitivity, with a marked decline of postural control and gait in the afternoon. In spite of a strong relationship between plantar cutaneous sensitivity and gait/postural control, the decline in postural control and gait observed in the afternoon could not be related to plantar sensation. It might rather relate to a cognitive function which is known to peak early in human circadian rhythms and to have a greater contribution in postural control regulation in the elderly than in young healthy subjects.     

Sensitivity of a subject-specific musculoskeletal model to the uncertainties on the joint axes location

Subject-specific musculoskeletal models have become key tools in the clinical decision-making process. However, the sensitivity of the calculated solution to the unavoidable errors committed while deriving the model parameters from the available information is not fully understood. The aim of this study was to calculate the sensitivity of all the kinematics and kinetics variables to the inter-examiner uncertainty in the identification of the lower limb joint models. The study was based on the computer tomography of the entire lower-limb from a single donor and the motion capture from a body-matched volunteer. The hip, the knee and the ankle joint models were defined following the International Society of Biomechanics recommendations. Using a software interface, five expert anatomists identified on the donor's images the necessary bony locations five times with a three-day time interval. A detailed subject-specific musculoskeletal model was taken from an earlier study, and re-formulated to define the joint axes by inputting the necessary bony locations. Gait simulations were run using OpenSim within a Monte Carlo stochastic scheme, where the locations of the bony landmarks were varied randomly according to the estimated distributions. Trends for the joint angles, moments, and the muscle and joint forces did not substantially change after parameter perturbations. The highest variations were as follows: (a) 11° calculated for the hip rotation angle, (b) 1% BW × H calculated for the knee moment and (c) 0.33 BW calculated for the ankle plantarflexor muscles and the ankle joint forces. In conclusion, the identification of the joint axes from clinical images is a robust procedure for human movement modelling and simulation.     

Kinetic-based indexes for the functional evaluation of gait in diplegic children: a preliminary report

Abstract

We evaluated the feasibility of a set of indexes based on ground reaction forces to discriminate between the degree of severity of spastic diplegia, identified via Gross Motor Function Classification System (GMFCS). A stepwise discriminant ordinal regression analysis performed on a sample of 58 children returned a subset of variables related to the ratio between braking and propulsive vertical forces and anteroposterior timings. Rather, parameters concerning bilateral symmetry were poorly discriminating. The relative simplicity of the selected indexes allows for their easy implementation on existing gait analysis applications for screening purposes.     

Allosteric regulation of cardiac sarcoplasmic reticulum Ca ATPase: a comparative study

Summary The mechanisms of allosteric regulation of the Ca-ATPases of cardiac and skeletal sarcoplasmic reticulum by ATP have been compared. Although both enzymes showed stimulation of ATPase activity by ATP, the cardiac enzyme did not show the plateau in ATPase activity at 10–100M ATP seen with the skeletal enzyme. Likewise the phosphoenzyme (EP) levels did not plateau with the cardiac enzyme as they did with the skeletal enzyme. The apparent negative cooperatively which was seen in the kinetics of ATP hydrolysis at low ATP concentrations was not due to negative cooperatively in substrate binding to either enzyme. The cardiac enzyme did show, however, much higher affinity for the ATP analog, AMPPCP, which helps explain how AMPPCP blocks ATPase activity in the cardiac enzyme and stimulates ATPase activity in the skeletal enzyme. Fluorescein isothiocyanate was used to determine if allosteric regulation takes place through site-site interactions in oligomers. The 1 to 1 ratio between AMPPCP binding sites and FITC binding sites eliminated allosteric regulation by effector sites in both enzymes. The allosteric mechanism which remained was one in which the active-site becomes an effector-site by the early departure of ADP in the reaction mechanism. The step stimulated by the binding of ATP at the active-site turned effector-site was a nonphosphorylated form of the enzyme in cardiac sarcoplasmic reticulum and a phosphorylated form in skeletal sarcoplasmic reticulum.Abbreviations AMPPCP Adenylyl Methylenediphosphonate - EGTA Ethyleneglycol Bis(amino-ethyl ether)-N,N,N,N Tetraacetic Acid - Pi Inorganic Phosphate - EP Phosphorylated Enzyme - FITC Fluorescein Isothiocyanate - MOPS 3-(N-morpholino)-Propanesulfonic Acid - v/EP ratio of calcium dependent ATPase activity to phosphoenzyme level - V initial rate of phosphoenzyme formation - LSSR Light Sarcoplasmic Reticulum - CSR Cardiac Sarcoplasmic Reticulum.     

Molecular modeling study for the design of novel acetyl-CoA carboxylase inhibitors using 3D QSAR,molecular docking and dynamic simulations

Acetyl-CoA carboxylase (ACC) enzyme plays an important role in the regulation of biosynthesis and oxidation of fatty acids. ACC is a recognized drug target for the treatment of obesity and diabetes. Combination of ligand and structure-based in silico methods along with activity and toxicity prediction provides best lead compounds in the drug discovery process. In this study, a data-set of 100 ACC inhibitors were used for the development of comparative molecular field analysis (CoMFA) and comparative molecular similarity index matrix analysis (CoMSIA) models. The generated contour maps were used for the design of novel ACC inhibitors. CoMFA and CoMSIA models were used for the predication of activity of designed compounds. In silico toxicity risk prediction study was carried out for the designed compounds. Molecular docking and dynamic simulations studies were performed to know the binding mode of designed compounds with the ACC enzyme. The designed compounds showed interactions with key amino acid residues important for catalysis, and good correlation was observed between binding free energy and inhibition of ACC.