a classification of two dimensional tube domains we give a complete classification of two dimensional tube domains up to biholomorphic equivalence as a consequence we obtain a tube domain with a remarkable property which gives a counterexample to the claim of dadok and yang on the structure of tube domains

take off analysis of the olympic ski jumping competition hs 106m abstract the take off phase approximately 6 m of the jumps of all athletes participating in the individual hs 106 m hill ski jumping competition at the torino olympics was filmed with two high speed cameras the high altitude of the pragelato ski jumping venue 1600 m and slight tail wind in the final jumping round were expected to affect the results of this competition the most significant correlation with the length of the jump was found in the in run velocity r 0 628 p n 50 this was a surprise in olympic level ski jumping and suggests that good jumpers simply had smaller friction between their skis and the in run tracks and or the aerodynamic quality of their in run position was better angular velocity of the hip joint of the best jumpers was also correlated with jumping distance r 0 651 p n 10 the best jumpers in this competition exhibited very different take off techniques but still they jumped approximately the same distance this certainly improves the interests in ski jumping among athletes and spectators the comparison between the take off techniques of the best jumpers showed that even though the more marked upper body movement creates higher air resistance it does not necessarily result in shorter jumping distance if the exposure time to high air resistance is not too long a comparison between the first and second round jumps of the same jumpers showed that the final results in this competition were at least partly affected by the wind conditions

kinetic analysis of the lower limbs during walking what information can be gained from a three dimensional model kinetic analyses joint moments powers and work of the lower limbs were performed during normal walking to determine what further information can be gained from a three dimensional model over planar models it was to be determined whether characteristic moment and power profiles exist in the frontal and transverse planes across subjects and how much work was performed in these planes kinetic profiles from nine subjects were derived using a three dimensional inverse dynamics model of the lower limbs and power profiles were then calculated by a dot product of the angular velocities and joint moments resolved in a global reference system characteristic joint moment profiles across subjects were found for the hip knee and ankle joints in all planes except for the ankle frontal moment as expected the major portion of work was performed in the plane of progression since the goal of locomotion is to support the body against gravity while generating movements which propel the body forward however the results also showed that substantial work was done in the frontal plane by the hip during walking 23 of the total work at that joint the characteristic joint profiles suggest defined motor patterns and functional roles in the frontal and transverse planes kinetic analysis in three dimensions is necessary particularly if the hip joint is being examined as a substantial amount of work was done in the frontal plane of the hip to control the pelvis and trunk against gravitational forces

automorphisms of tube domains and spherical hypersurfaces 0 introduction let q c r be an open convex set containing no lines and let d q x ir x iy e cn y e r be the tube domain over u the domain d is biholomorphically equivalent to a bounded pseudoconvex domain and aut d f d di f a biholomorphic map is a lie group when q is a bounded smooth strictly convex domain the group aut d was shown 5 to consist of real affine linear transformations in that same paper the cauchy riemann structure of the boundary ad aq ir was studied in terms of the affine structure of an

adjustments to zatsiorsky seluyanov s segment inertia parameters zatsiorsky et al in contemporary problems in biomechanics pp 272 291 crc press massachusetts 1990a obtained by means of a gamma ray scanning technique the relative body segment masses center of mass cm positions and radii of gyration for samples of college aged caucasian males and females although these data are the only available and comprehensive set of inertial parameters regarding young adult caucasians they have been rarely utilized for biomechanical analyses of subjects belonging to the same or a similar population the main reason is probably that zatsiorsky et al used bony landmarks as reference points for locating segment cms and defining segment lengths some of these landmarks were markedly distant from the joint centers currently used by most researchers as reference points the purpose of this study was to adjust the mean relative cm positions and radii of gyration reported by zatsiorsky et al in order to reference them to the joint centers or other commonly used landmarks rather than the original landmarks the adjustments were based on a number of carefully selected sources of anthropometric data

dynamic stability and compensatory stepping responses during anterior gait slip perturbations in people with chronic hemiparetic stroke abstract to examine the control of dynamic stability and characteristics of the compensatory stepping responses to an unexpected anterior gait slip induced under the non involved limb in people with hemi paretic stroke pwhs and to examine any resulting adaptive changes in these on the second slip due to experience from prior slip exposure ten pwhs experienced overground slip s1 during walking on the laboratory walkway after 5 8 regular walking rw trials followed by a second consecutive slip trial s2 the slip outcome backward loss of balance blob and no loss of balance nlob and com state i e its com position and velocity stability were examined between the rw and s1 and s1 and s2 at touchdown td of non involved limb and at liftoff lo of the contralateral limb at td there was no difference in stability between rw and s1 however at lo subjects demonstrated a lower stability on s1 than rw resulting in a 100 backward loss of balance blob with compensatory stepping response recovery step rs 4 10 or aborted step as 6 10 on s2 although there was no change in stability at td there was a significant improvement in stability at lo with a 40 decrease in blob there was also a change in step strategy with a decrease in as response 60 to 35 p

validation of net joint loads calculated by inverse dynamics in case of complex movements application to balance recovery movements the joint forces and moments driving the motion of a human subject are classically computed by an inverse dynamic calculation however even if this process is theoretically simple many sources of errors may lead to huge inaccuracies in the results moreover a direct comparison with in vivo measured loads or with gold standard values from literature is only possible for very specific studies therefore assessing the inaccuracy of inverse dynamic results is not a trivial problem and a simple method is still required this paper presents a simple method to evaluate both 1 the consistency of the results obtained by inverse dynamics 2 the influence of possible modifications in the inverse dynamic hypotheses this technique concerns recursive calculation performed on full kinematic chains and consists in evaluating the loads obtained by two different recursive strategies it has been applied to complex 3d whole body movements of balance recovery a recursive newton euler procedure was used to compute the net joint loads two models were used to represent the subject bodies considering or not the upper body as a unique rigid segment the inertial parameters of the body segments were estimated from two different sets of scaling equations de leva p 1996 adjustments to zatsiorsky suleyanov s segment inertia parameters journal of biomechanics 29 1223 1230 dumas r cheze l verriest j p 2006b adjustments to mcconville et al and young et al body segment inertial parameters journal of biomechanics in press using this comparison technique it has been shown that for the balance recovery motions investigated 1 the use of the scaling equations proposed by dumas et al instead of those proposed by de leva improves the consistency of the results average relative influence up to 30 for the transversal moment 2 the arm motions dynamically influence the recovery motion in a non negligible way average relative influence up to 15 and 30 for the longitudinal force and the transversal moment respectively

a new geometric based model to accurately estimate arm and leg inertial estimates segment estimates of mass center of mass and moment of inertia are required input parameters to analyze the forces and moments acting across the joints the objectives of this study were to propose a new geometric model for limb segments to evaluate it against criterion values obtained from dxa and to compare its performance to five other popular models twenty five female and 24 male college students participated in the study for the criterion measures the participants underwent a whole body dxa scan and estimates for segment mass center of mass location and moment of inertia frontal plane were directly computed from the dxa mass units for the new model the volume was determined from two standing frontal and sagittal photographs each segment was modeled as a stack of slices the sections of which were ellipses if they are not adjoining another segment and sectioned ellipses if they were adjoining another segment e g upper arm and trunk length of axes of the ellipses was obtained from the photographs in addition a sex specific non uniform density function was developed for each segment a series of anthropometric measurements were also taken by directly following the definitions provided of the different body segment models tested and the same parameters determined for each model comparison of models showed that estimates from the new model were consistently closer to the dxa criterion than those from the other models with an error of less than 5 for mass and moment of inertia and less than about 6 for center of mass location

whole body inverse dynamics over a complete gait cycle based only on measured kinematics this paper presents a three dimensional 3d whole body multi segment model for inverse dynamics analysis over a complete gait cycle based only on measured kinematic data the sequence of inverse dynamics calculations differs significantly from the conventional application of inverse dynamics using force plate data a new validated smooth transition assumption was used to solve the indeterminacy problem in the double support phase kinematic data is required for all major body segments and hence a whole body gait measurement protocol is presented finally sensitivity analyses were conducted to evaluate the effects of digital filtering and body segment parameters on the accuracy of the prediction results the model gave reasonably good estimates of sagittal plane ground forces and moment however the estimates in the other planes were less good which we believe is largely due to their small magnitudes in comparison to the sagittal forces and moment the errors observed are most likely caused by errors in the kinematic data resulting from skin movement artefact and by errors in the estimated body segment parameters a digital filtering cut off frequency of 4 5 hz was found to produce the best results it was also shown that errors in the mass properties of body segments can play a crucial role with changes in properties sometimes having a disproportionate effect on the calculated ground reactions the implication of these results is that even when force plate data is available the estimated joint forces are likely to suffer from similar errors

lower extremity control during turns initiated with and without hip external rotation the pirouette turn is often initiated in neutral and externally rotated hip positions by dancers this provides an opportunity to investigate how dancers satisfy the same mechanical objectives at the whole body level when using different leg kinematics the purpose of this study was to compare lower extremity control strategies during the turn initiation phase of pirouettes performed with and without hip external rotation skilled dancers n 5 performed pirouette turns with and without hip external rotation joint kinetics during turn initiation were determined for both legs using ground reaction forces grfs and segment kinematics hip muscle activations were monitored using electromyography using probability based statistical methods variables were compared across turn conditions as a group and within dancer despite differences in grfs and impulse generation between turn conditions at least 90 of each grf was aligned with the respective leg plane a majority of the net joint moments at the ankle knee and hip acted about an axis perpendicular to the leg plane however differences in shank alignment relative to the leg plane affected the distribution of the knee net joint moment when represented with respect to the shank versus the thigh during the initiation of both turns most participants used ankle plantar flexor moments knee extensor moments flexor and abductor moments at the push leg s hip and extensor and abductor moments at the turn leg s hip representation of joint kinetics using multiple reference systems assisted in understanding control priorities

estimation of the centre of rotation a methodological contribution the location of the centre of rotation of human joints that can be modelled as a spherical hinge can be estimated using kinematics information about the two adjacent bony segments involved recorded while the subject makes them move one relative to the other functional method in order to solve the relevant analytical problem several algorithms have been proposed most recently two methods one based on a spherical best fit approach and another based on the reuleaux construction have been presented as being different and submitted to comparative evaluation this paper modifies the second method taking all information in the data set into account and shows that having done this the two methods coincide analytically

a system to measure the kinematics during the entire ski jump sequence using inertial sensors three dimensional analysis of the entire sequence in ski jumping is recommended when studying the kinematics or evaluating performance camera based systems which allow three dimensional kinematics measurement are complex to set up and require extensive post processing usually limiting ski jumping analyses to small numbers of jumps in this study a simple method using a wearable inertial sensors based system is described to measure the orientation of the lower body segments sacrum thighs shanks and skis during the entire jump sequence this new method combines the fusion of inertial signals and biomechanical constraints of ski jumping its performance was evaluated in terms of validity and sensitivity to different performances based on 22 athletes monitored during daily training the validity of the method was assessed by comparing the inclination of the ski and the slope at landing point and reported an error of 0 2 4 8 the validity was also assessed by comparison of characteristic angles obtained with the proposed system and reference values in the literature the differences were smaller than 6 for 75 of the angles and smaller than 15 for 90 of the angles the sensitivity to different performances was evaluated by comparing the angles between two groups of athletes with different jump lengths and by assessing the association between angles and jump lengths the differences of technique observed between athletes and the associations with jumps length agreed with the literature in conclusion these results suggest that this system is a promising tool for a generalization of three dimensional kinematics analysis in ski jumping

knee and ankle joint torque angle relationships of multi joint leg extension abstract the force length relation f l r is an important property of skeletal muscle to characterise its function whereas for in vivo human muscles torque angle relationships t a r represent the maximum muscular capacity as a function of joint angle however since in vivo force torque length data is only available for rotational single joint movements the purpose of the present study was to identify torque angle relationships for multi joint leg extension therefore inverse dynamics served for calculation of ankle and knee joint torques of 18 male subjects when performing maximum voluntary isometric contractions in a seated leg press measurements in increments of 10 knee angle from 30 to 100 knee flexion resulted in eight discrete angle configurations of hip knee and ankle joints for the knee joint we found an ascending descending t a r with a maximum torque of 289 5 43 3 n m which closely matches literature data from rotational knee extension in comparison to literature we observed a shift of optimum knee angle towards knee extension in contrast the t a r of the ankle joint vastly differed from relationships obtained for isolated plantar flexion for the ankle t a r derived from multi joint leg extension subjects operated over different sections of the force length curve but the ankle t a r derived from isolated joint efforts was over the ascending limb for all subjects moreover mean maximum torque of 234 7 56 6 n m exceeded maximal strength of isolated plantar flexion 185 7 27 8 n m from these findings we conclude that muscle function between isolated and more physiological multi joint tasks differs this should be considered for ergonomic and sports optimisation as well as for modelling and simulation of human movement

computation of trunk stability in forward perturbations effects of preload perturbation load initial flexion and abdominal preactivation spine stability demand influences active passive coordination of the trunk response especially during sudden perturbations the objective of this study was to look at the role of passive stationary active and reflexive subsystems on spinal stability spine stability was evaluated here during pre and post perturbation phases by computing the minimum i e critical muscle stiffness coefficient required to maintain stability the effects of pre perturbation conditions preloading initial posture and abdominal antagonistic coactivation as well as perturbation magnitude were studied results revealed that higher preload initially flexed trunk posture and abdominal pre activation enhanced pre perturbation stiffness and stability in contrast to the preload however larger sudden load initial flexion and abdominal preactivation significantly increased post perturbation stability margin as a result much lower critical muscle stiffness coefficient was required post perturbation compared to the pre perturbation phase the trunk stiffness and stability substantially increased post perturbation demanding thus a much lower critical muscle stiffness coefficient overall these findings highlight the crucial role of the ligamentous spine and muscles in both passive and active states in augmenting the trunk stiffness and hence stability during pre and post perturbation phases a role much evident in the presence of initial trunk flexion

point of optimal kinematic error improvement of the instantaneous helical pivot method for locating centers of rotation this paper proposes a variation of the instantaneous helical pivot technique for locating centers of rotation the point of optimal kinematic error poke which minimizes the velocity at the center of rotation may be obtained by just adding a weighting factor equal to the square of angular velocity in woltring s equation of the pivot of instantaneous helical axes piha calculations are simplified with respect to the original method since it is not necessary to make explicit calculations of the helical axis and the effect of accidental errors is reduced the improved performance of this method was validated by simulations based on a functional calibration task for the gleno humeral joint center noisy data caused a systematic dislocation of the calculated center of rotation towards the center of the arm marker cluster this error in piha could even exceed the effect of soft tissue artifacts associated to small and medium deformations but it was successfully reduced by the poke estimation

a survey of formal methods for determining the centre of rotation of ball joints abstract the determination of an accurate centre of rotation cor from segment marker positions is of interest across a wide range of applications but particularly for clinical gait analysis and for estimating the hip joint centre during surgical intervention of the knee for limb alignment purposes for the first time in this survey of formal methods we classify analyse and compare different methods geometric algebraic bias compensated algebraic and pratt sphere fit methods as well as the centre transformation technique the holzreiter approach the helical pivot technique the schwartz transformation techniques the minimal amplitude point method and the stoddart approach for the determination of spherical joint centres from marker position data in addition we propose a new method the symmetrical cor estimation or score in which the coordinates of the joint centre must only remain constant relative to each segment thus not requiring the assumption that one segment should remain at rest for each method 1000 cor estimations were analysed with the application of isotropic independent and identically distributed gaussian noise standard deviation 0 1 cm to each of the marker positions to all markers on the segment simultaneously and the two in combination for the test conditions used here most techniques were capable of determining the cor to within 0 3 cm as long as the spherical range of motion rom of the joint was 45 or more under the most stringent conditions tested however the score was capable of best determining the cor to within approximately 1 2 mm with a rom of 20 the correct selection and application of these methodologies should help improve the accuracy of surgical navigation and clinical kinematic measurement

moving beyond quiet stance applicability of the inverted pendulum model to stooping and crouching postures background currently it is unknown whether the inverted pendulum model is applicable to stooping or crouching postures therefore the aim of this study was to determine the degree of applicability of the inverted pendulum model to these postures via examination of the relationship between the centre of mass com acceleration and centre of pressure cop com difference methods ten young adults held static standing stooping and crouching postures each for 20 s for both the anterior posterior ap and medio lateral ml directions the time varying com acceleration and the cop com were computed and the relationship between these two variables was determined using pearson s correlation coefficients additionally in both directions the average absolute com acceleration average absolute cop com signal and the inertial component i e i wh were compared across postures results pearson correlation coefficients revealed a significant negative relationship between the com acceleration and cop com signal for all comparisons regardless of the direction p 0 001 while no effect of posture was observed in the ap direction p 0 463 in the ml direction the correlation coefficients for stooping were different i e stronger than standing p 0 008 regardless of direction the average absolute com acceleration for both the stooping and crouching postures was greater than standing p 0 002 conclusion the high correlations indicate that the inverted pendulum model is applicable to stooping and crouching postures due to their importance in completing activities of daily living there is merit in determining what type of motor strategies are used to control such postures and whether these strategies change with age

prediction of joint center location by customizable multiple regressions application to clavicle scapula and humerus accurate spatial location of joint center jc is a key issue in motion analysis since jc locations are used to define standardized anatomical frames in which results are represented accurate and reproducible jc location is important for data comparison and data exchange this paper presents a method for jc locations based on the multiple regression algorithms without preliminary assumption on the behavior of the joint of interest regression equations were obtained from manually palpable als on each bone of interest results are presented for all joint surfaces found on the clavicle scapula and humeral bone mean accuracy errors on the jc locations obtained on dry bones were 5 2 2 5 mm for the humeral head 2 5 1 1 mm for the humeral trochlea 2 3 0 9 mm for the humeral capitulum 8 2 3 9 mm for the scapula glenoid cavity 7 2 3 2 mm for the scapular aspect of the acromio clavicular joint 3 5 1 8 mm for the clavicular aspect of the sternoclavicular joint and 3 2 1 4 mm for the clavicular aspect of the acromio clavicular joint in vitro and in vivo validation accuracy was 5 3 and 8 5 mm respectively for the humeral head center location regression coefficients for joint radius dimension and joint surface orientation were also processed and reported in this paper

are the maximum shortening velocity and the shape parameter in a hill type model of whole muscle related to activation abstract mathematical models of the inter relationship of muscle force velocity and activation are useful in forward dynamic simulations of human movement tasks the objective of this work was to determine whether the parameters maximum shortening velocity v max and shape parameter k of a hill type muscle model interrelating muscle force velocity and activation are themselves dependent on the activation to fulfill this objective surface emg signals from four muscles as well as the kinematics and kinetics of the arm were recorded from 14 subjects who performed rapid release elbow extension tasks at 25 50 75 and 100 activation mvc the experimental elbow flexion angle was tracked by a forward dynamic simulation of the task in which v max and k of the triceps brachii were varied at each activation level to minimize the difference between the simulated and experimental elbow flexion angle because a preliminary analysis demonstrated no dependency of k on activation additional simulations were performed with constant k values of 0 15 0 20 and 0 25 the optimized values of v max normalized to the average value within a subject were then regressed onto the activation normalized v max depended significantly on the activation p k furthermore the estimated v max values were not sensitive to the selected k value the results support the use of hill type models in which v max depends on activation in forward dynamic simulations modeling muscles with mixed fiber type composition recruited in the range of 25 100 activation the use of more accurate models will lend greater confidence to the results of forward dynamic simulations

expressing the joint moments of drop jumps and sidestep cutting in different reference frames does it matter abstract joint moments help us understand joint loading and muscle function during movement however the interpretation depends on the choice of reference frame but the different reference frames have not been compared in dynamic high impact sporting movements we have compared the magnitude and the resulting ranking of hip and knee joint moments expressed in the laboratory coordinate system the local system of the distal segment and projected or decomposed to the joint coordinate system jcs axes hip and knee joint moments of drop jumps and sidestep cutting in 70 elite female handball players were calculated based on recordings from an eight camera 240 hz system and two force platforms and expressed with the four methods the greatest variations in magnitude between conditions were seen for drop jump hip internal rotation range 0 31 0 71 nm kg and sidestep cutting knee flexion 2 87 3 39 nm kg and hip internal rotation 0 87 2 36 nm kg and knee internal rotation 0 10 0 40 nm kg moments the rank correlations were highest between conditions for flexion moments 0 88 1 00 and sidestep cutting abduction moments 0 71 0 98 the rank correlations ranged from 0 64 to 0 73 for drop jump knee abduction moments and between 0 17 and 0 67 for hip and knee internal rotation moments expression of joint moments in different reference systems affects the magnitude and ranking of athletes this lack of consistency may complicate the comparison and combination of results projection to the jcs is the only method where joint moments correspond to muscle and ligament loading more widespread adoption of this convention could facilitate comparison of studies and ease the interpretation of results

estimation of centre of gravity movements in sitting posture application to trunk backward tilt abstract the aim of this study was to highlight in sitting posture the value of distinguishing between the movements of the vertical projection of the centre of gravity cgv and its difference from the centre of pressure cp cgv a protocol for healthy young trained adults consisting in tilting their trunk backward or keeping it vertical was used a frequency analysis shows that statistically significant effects were only seen on cp cgv movements the rms increased by 37 p 0 004 while the mpf decreased by 5 p 0 016 suggesting an increased muscular activity in these tilting postures in contrast no statistically significant effects on cp and cgv were reported these data highlight the advantage in sitting posture of splitting overall cp displacements into basic components i e cgv and cp cgv each of them having a biomechanical significance

effects of age and step length on joint kinetics during stepping task following a balance perturbation a stepping response is commonly used to regain support and the distance of the recovery step can vary to date no other studies have examined joint kinetics in young and old adults during increasing step distances when participants are required to bring their rear foot forward therefore the purpose of this study was to examine age related differences in joint kinetics with increasing step distance twenty young and 20 old adults completed the study participants completed a step starting from double support at an initial distance equal to the individual s average step length the distance was increased by 10 body height until an unsuccessful attempt a one way repeated measures anova was used to determine the effects of age on joint kinetics during the maximum step distance a two way repeated measures mixed model anova was used to determine the effects of age step distance and their interaction on joint kinetics during the first three step distances for all participants young adults completed a significantly longer step than old adults during the maximum step in general kinetic measures were greater in the young than in the old as step distance increased all but one kinetic measure increased for both young and old adults this study has shown the ability to discriminate between young and old adults and could potentially be used in the future to distinguish between fallers and non fallers

lower extremity control and dynamics during backward angular impulse generation in forward translating tasks observation of complex whole body movements suggests that the nervous system coordinates multiple operational subsystems using some type of hierarchical control when comparing two forward translating tasks performed with and without backward angular impulse we have learned that both trunk leg coordination and reaction force time characteristics are significantly different between tasks this led us to hypothesize that differences in trunk leg coordination and reaction force generation would induce between task differences in the control of the lower extremity joints during impulse generation phase of the tasks eight highly skilled performers executed a series of forward jumps with and without backward rotation reverse somersault and reverse timer respectively sagittal plane kinematics reaction forces and electromyograms of lower extremity muscles were acquired during the take off phase of both tasks lower extremity joint kinetics were calculated using inverse dynamics the results demonstrated between task differences in the relative angles between the lower extremity segments and the net joint forces reaction force and the joint angular velocity profiles significantly less knee extensor net joint moments and net joint moment work and greater hip extensor net joint moments and net joint moment work were observed during the push interval of the reverse somersault as compared to the reverse timer between task differences in lower extremity joint kinetics were regulated by selectively activating the bi articular muscles crossing the knee and hip these results indicate that between task differences in the control of the center of mass relative to the reaction force alters control and dynamics of the multijoint lower extremity subsystem

a hip joint kinematics driven model for the generation of realistic thigh soft tissue artefacts in human movement analysis accuracy and robustness of the algorithms used to determine the location of centres of rotation from stereophotogrametric data depend mainly on their capacity to deal with the artefacts due to soft tissue deformation sta while evaluating these algorithms using a mathematical simulation approach effectual realizations of stas are needed this study aimed at accomplishing this objective by modelling stas in twelve selected areas of the thigh as a linear function of the hip angles assuming no knee joint movement the proposed model was calibrated and assessed using ex vivo experiments this entailed that only the component of the sta due to skin stretching was accounted for photogrammetric data of markers placed on the skin and on hip bone and femur pins were recorded during passive flexion extension ab adduction rotation and circumduction of the hip joint artefact skin marker displacements were represented in a femur embedded anatomical frame model parameters were estimated by minimizing the least squares difference between measured and modelled stas the sta affecting a skin marker placed in a given thigh location of a given subject could be modelled with a high accuracy median root mean square difference over 4 subjects 3 trials 12 markers 3 coordinates 0 8 mm inter quartile range 1 0 mm this was also true for a hip joint movement different from the one used to calibrate the model high inter subject variability of the model parameters confirmed the subject dependency of the phenomenon

conjugate asymptotic properties of spectra and correlations we examine a general technique for deriving the small time asymptotic expansion of a correlation from the large frequency asymptotic form of the associated spectrum conjugate asymptotic properties our analysis explicitly takes into account the form of approach of the spectrum to its asymptotic limit i e asymptotic convergence and the resulting impact on the correlation asymptotic expansion we fully evaluate the two lowest order terms in the small time asymptotic expansion of the correlation for the important special case of the large frequency asymptotic behaviour of the spectrum being a negative power of frequency included in our analysis is a determination of sufficient conditions on the rapidity of approach of the spectrum towards its asymptotic form i e convergence rate for the derived correlation asymptotic approximation to be accurate to second order we comment on how small time must be for our correlation asymptotic approximations to be valid to motivate this analysis we propose circumstances under which these results could be of utility in physics

corner height influences center of mass kinematics and path trajectory during turning despite the prevalence of directional changes during every day gait relatively little is known about turning compared to straight gait while the center of mass com movement during straight gait is well characterized the com trajectory and the factors that influence it are less established for turning this study investigated the influence of a corner s height on the com trajectory as participants walked around the corner ten participants 25 3 3 74 years performed both 90 step and spin turns to the left at self selected slow normal and fast speeds while walking inside a marked path a pylon was placed on the inside corner of the path four different pylon heights were used to correspond to heights of everyday objects 0 cm no object 63 cm box crate 104 cm desk table counter 167 cm shelf cabinet obstacle height was found to significantly affect the com trajectory taller obstacles resulted in more distance between the corner and the com and between the corner and the cop taller obstacles also were associated with greater curvature in the com trajectory indicating a smaller turning radius despite the constant 90 corner taller obstacles correlated to an increased required coefficient of friction rcof due to the smaller turning radii taller obstacles also tended towards greater mediolateral ml com cop angles contrary to the initial hypothesis additionally the com was found to remain outside the base of support bos for the entire first half of stance phase for all conditions indicating a high risk of falls resulting from slips

segment interaction in sprint start analysis of 3d angular velocity and kinetic energy in elite sprinters the aim of the present study was to measure during a sprint start the joint angular velocity and the kinetic energy of the different segments in elite sprinters this was performed using a 3d kinematic analysis of the whole body eight elite sprinters 10 30 0 14s 100 m time equipped with 63 passive reflective markers realised four maximal 10 m sprints start on an indoor track an opto electronic motion analysis system consisting of 12 digital cameras 250 hz was used to collect the 3d marker trajectories during the pushing phase on the blocks the 3d angular velocity vector and its norm were calculated for each joint the kinetic energy of 16 segments of the lower and upper limbs and of the total body was calculated the 3d kinematic analysis of the whole body demonstrated that joints such as shoulders thoracic or hips did not reach their maximal angular velocity with a movement of flexion extension but with a combination of flexion extension abduction adduction and internal external rotation the maximal kinetic energy of the total body was reached before clearing block respectively 537 59 3 j vs 514 9 66 0 j p or 0 01 these results suggested that a better synchronization between the upper and lower limbs could increase the efficiency of pushing phase on the blocks besides to understand low interindividual variances in the sprint start performance in elite athletes a 3d complete body kinematic analysis shall be used

the effect on conventional gait model kinematics and kinetics of hip joint centre equations in adult healthy gait abstract the conventional gait model cgm needs to benefit from large investigations on localization of the hip joint centre hjc incorrect positions from the native equations were demonstrated sangeux et al 2014 harrington et al 2007 more accurate equations were proposed but their impact on kinematics and kinetic cgm outputs was never evaluated this short communication aims at examining if adoption of new hjc equations would alter standard cgm outputs sixteen able bodied participants underwent a full 3 d optoelectronic gait analysis followed by a 3 d ultrasound localization of their hips data were processed through the open source python package pycgm2 replicating kinematic and kinetic processing of the native cgm compared with 3d ultrasound location hara equations improved the accuracy of sagittal plane kinematics 0 6 and kinetics 0 02 n m kg 1 for the hip the worst case participant exhibited harrington s equations reached a deviation of 3 for the sagittal kinematics in the coronal plane hara and harrington equations presented similar differences 1 for the hip whilst davis equations had the largest deviation for hip abduction 2 7 and hip abductor moment 0 10 n m kg 1 both harrington and hara equations improved the cgm location of the hjc hara equations improved results in the sagittal plane plus utilise a single anthropometrics measurement leg length that may be more robust however neither set of equations had significant effect on kinematics we reported some effects on kinetics particularly in the coronal plane which warrant caution in interpreting outputs using different sets of equations

on the relevance of residual force enhancement for everyday human movement abstract although residual force enhancement rfe i e enhanced force after active muscle stretch is shown to be present in voluntarily activated human muscles its relevance for everyday human movement is still elusive natural human motion is mainly composed of voluntarily submaximally activated muscle contractions driving coordinated multi joint movements up to now there has been no study that directly investigated the presence of rfe following stretch when performing a submaximal multi joint movement for this purpose n 13 subjects performed feedback controlled bilateral leg extensions at the level of 30 maximum voluntary activation in a motor driven leg press dynamometer isometric eccentric isometric and purely isometric contractions were arranged in a randomized experimental protocol kinematics forces and muscular activity were measured using optical motion tracking 3d force plates and emg of 9 lower extremity muscles anova identified significant rfe of external reaction force and knee extension and plantar flexion torque calculated by inverse dynamics enhanced force and torque ranged between 3 and 22 and was present for up to 22 s post stretch in spite of motor redundancy for solving a given task no differences between contraction conditions were observed for any of the analyzed muscles except for tibialis anterior on the basis of our results rfe is present in everyday alike human movement and might be an evolutionary optimization mechanism to enhance muscular performance at a given amount of energetic effort

to what extent is joint and muscle mechanics predicted by musculoskeletal models sensitive to soft tissue artefacts musculoskeletal models are widely used to estimate joint kinematics intersegmental loads and muscle and joint contact forces during movement these estimates can be heavily affected by the soft tissue artefact sta when input positional data are obtained using stereophotogrammetry but this aspect has not yet been fully characterised for muscle and joint forces this study aims to assess the sensitivity to the sta of three open source musculoskeletal models implemented in opensim a baseline dataset of marker trajectories was created for each model from experimental data of one healthy volunteer five hundred sta realizations were then statistically generated using a marker dependent model of the pelvis and lower limb artefact and added to the baseline data the sta s impact on the musculoskeletal model estimates was finally quantified using a monte carlo analysis the modelled sta distributions were in line with the literature observed output variations were comparable across the three models and sensitivity to the sta was evident for most investigated quantities shape magnitude and timing of the joint angle and moment time histories were not significantly affected throughout the entire gait cycle whereas magnitude variations were observed for muscle and joint forces ranges of contact force variations differed between joints with hip variations up to 1 8 times body weight observed variations of more than 30 were observed for some of the muscle forces in conclusion musculoskeletal simulations using stereophotogrammetry may be safely run when only interested in overall output patterns caution should be paid when more accurate estimated values are needed

knee kinematics and kinetics during shuttle run cutting comparison of the assessments performed with and without the point cluster technique the differences between the assessments performed with and without the point cluster technique pct for knee joint motions during the high risk movements associated with non contact anterior cruciate ligament acl injuries have not been reported this study aims to examine the differences between pct and non pct assessments for knee joint angles and moments during shuttle run cutting fourteen high school athletes performed a maximal effort shuttle run cutting task motion data were collected by an 8 camera motion analysis system at 200 hz and ground reaction force data were recorded using a force plate at 1000 hz in both pct and non pct approaches the knee joint angles were calculated using euler angle rotations and the knee joint moments were obtained by solving the newton euler equations using an inverse dynamics technique for the extension flexion angle good agreement was measured between pct and non pct assessments the abduction angle obtained in the non pct assessment was smaller than that obtained with the pct an internal rotation angle was obtained in the pct assessment whereas a small external rotation angle was obtained in the non pct assessment for the knee joint moments good agreement between pct and non pct assessments was observed for all the components the differences in the knee joint angles were attributed in part to the differences in the position of the medial femoral epicondyle the results suggest that the acl injury risk during shuttle run cutting is estimated lower in the non pct assessment than in the pct assessment

does the anthropometric model influence whole body center of mass calculations in gait examining whole body center of mass com motion is one of method being used to quantify dynamic balance and energy during gait one common method for estimating the com position is to apply an anthropometric model to a marker set and calculate the weighted sum from known segmental com positions several anthropometric models are available to perform such a calculation however to date there has been no study of how the anthropometric model affects whole body com calculations during gait this information is pertinent to researchers because the choice of anthropometric model may influence gait research findings and currently the trend is to consistently use a single model in this study we analyzed a single stride of gait data from 103 young adult participants we compared the whole body com motion calculated from 4 different anthropometric models plagenhoef et al 1983 winter 1990 de leva 1996 pavol et al 2002 we found that anterior posterior motion calculations are relatively unaffected by the anthropometric model however medial lateral and vertical motions are significantly affected by the use of different anthropometric models our findings suggest that the researcher carefully choose an anthropometric model to fit their study populations when interested in medial lateral or vertical motions of the com our data can provide researchers a priori information on the model determination depending on the particular variable and how conservative they may want to be with com comparisons between groups

exploration of the validity of the two dimensional sagittal plane assumption in modeling the standing long jump most previous standing long jump studies have been based on the assumption of two dimensional sagittal plane motion with bilateral symmetry the purpose of this study was to investigate the validity of this assumption standing long jump trials were collected using six adult male participants each participant stood with a foot on each of two force plates and performed eight standing long jumps for maximal distance inverse dynamics analyses were performed for two dimensional 2d and three dimensional 3d models and joint moments powers and work values were compared the differences between these models with respect to the validity of the common planar jumping assumption were analyzed good agreement was observed between 2d and 3d methods for the lower body with minimal differences in sagittal plane moments power and work for the ankle knee and lower back there were significant but relatively small differences in the sagittal plane kinematics and kinetics at the hip for the upper body the results contradicted the sagittal plane assumption in that significant moments and power were generated about the abduction adduction axis of the shoulder and a similar amount of work was performed about both abduction adduction and flexion extension axes of the shoulder the elbow also showed significant differences in power and work these results indicate that an assumption of planar motion should be sufficient for many studies of the standing long jump that only examine lower body movement however for studies that include upper body motion diagnosing injury risk or investigating gender differences a 3d model may be more appropriate

a comparison of muscle energy models for simulating human walking in three dimensions the popular hill model for muscle activation and contractile dynamics has been extended with several different formulations for predicting the metabolic energy expenditure of human muscle actions these extended models differ considerably in their approach to computing energy expenditure particularly in their treatment of active lengthening and eccentric work but their predictive abilities have never been compared in this study we compared the predictions of five different hill based muscle energy models in 3d forward dynamics simulations of normal human walking in a data tracking simulation that minimized muscle fatigue the energy models predicted metabolic costs that varied over a three fold range 2 45 7 15 j m kg with the distinction arising from whether or not eccentric work was subtracted from the net heat rate in the calculation of the muscle metabolic rate in predictive simulations that optimized neuromuscular control to minimize the metabolic cost all five models predicted similar speeds step lengths and stance phase durations however some of the models predicted a hip circumduction strategy to minimize metabolic cost while others did not and the accuracy of the predicted knee and ankle angles and ground reaction forces also depended on the energy model used the results highlights the need to clarify how eccentric work should be treated when calculating muscle energy expenditure the difficulty in predicting realistic metabolic costs in simulated walking even with a detailed 3d musculoskeletal model the potential for using such models to predict energetically optimal gait modifications and the room for improvement in existing muscle energy models and locomotion simulation frameworks

influence of body segments parameters estimation models on inverse dynamics solutions during gait the purpose of the present study was to examine the in uence of anthropometric data on joint kinetics during gait we particularly focused on the sensitivity of inverse dynamics solutions to the use of models for body segment parameters bsp estimation six often used estimation models were selected to provide bsp values for the three segments of the lower limb kinematics and dynamics were sampled from seven subjects performing barefoot gait at three different speeds joint kinetics were estimated with the bottom up method using bsp values derived from each estimation model as anthropometric inputs the bsp estimates were highly sensitive to the model used with deviations ranging from at least 9 73 up to 60 maximal variations of peak values for the hip joint exion extension moment during the swing phase were 20 11 hence our ndings suggest that the in uence of bsp cannot be neglected observed deviations are especially due to the effect of varying simultaneously the mass moments of inertia and the center of mass location values according to the underlying relationship of interdependency linking each component considering both the differences found in joint kinetics and the level of accuracy of bsp models evidence is provided that using multiple regression bsp estimation functions derived from zatsiorsky and seluyanov biomechanics viii b 1983 pp 1152 1159 should be recommended to assess joint kinetics

a new method for estimating joint parameters from motion data joint centers and axes of rotation joint parameters are central to all branches of movement analysis in gait analysis the standard protocol used to determine hip and knee joint parameters is prone to errors arising from palpation anthropometric regression equations and misplaced alignment devices several alternative methods have been proposed but to date none have been shown to be accurate and reliable enough for use in the clinical setting this article describes a new method for joint parameter estimation the new method can be summarized as follows i the motions of two adjacent segments spanning a single joint are tracked ii the axis of rotation between every pair of observed segment configurations is computed iii the most likely intersection of all axes effective joint center and most likely orientation of the axes effective joint axis is found initial validation of the method was conducted on a hinged mechanical analog and a single healthy adult subject for the analog the center was found to be within 3 8 mm of the geometric center and 2 0 degrees of the geometric axis standard deviation for the adult subject hip centers varied on the order of 1 3 mm knee centers by 3 9 mm and knee axes by 2 0 degrees the results suggest that the new method is an objective precise and practical alternative to the standard clinical approach

effects of low pass filter combinations on lower extremity joint moments in distance running abstract inverse dynamics is a standard tool in biomechanics which requires low pass filtering of external force and kinematic signals unmatched filtering procedures are reported to affect joint moment amplitudes in high impact movements like landing or cutting but are also common in the analysis of distance running we analyzed the effects of cut off frequencies in 94 rearfoot runners at a speed of 3 5 m s additionally we investigated whether the evaluation of footwear interventions is affected by the choice of cut off frequencies we performed 3d inverse dynamics for the hip knee and ankle joints using different low pass filter cut off frequency combinations for a recursive fourth order butterworth filter we observed fluctuations of joint moment curves in the first half of stance which were most pronounced for the most unmatched cut off frequency combination kinematics 10 hz ground reaction forces grfs 100 hz and for more proximal joints peak sagittal plane hip joint moments were altered by 94 on average we observed a change in the ranking of subjects based on joint moment amplitude we found significant p

predicting dynamic postural instability using center of mass time to contact information our purpose was to determine whether spatiotemporal measures of center of mass motion relative to the base of support boundary could predict stepping strategies after upper body postural perturbations in humans we expected that inclusion of center of mass acceleration in such time to contact ttc calculations would give better predictions and more advanced warning of perturbation severity ttc measures were compared with traditional postural variables which do not consider support boundaries and with an inverted pendulum model of dynamic stability developed by hof et al 2005 the condition for dynamic stability journal of biomechanics 38 1 8 a pendulum was used to deliver sequentially increasing perturbations to 10 young adults who were strapped to a wooden backboard that constrained motion to sagittal plane rotation about the ankle joint subjects were instructed to resist the perturbations stepping only if necessary to prevent a fall peak center of mass and center of pressure velocity and acceleration demonstrated linear increases with postural challenge in contrast boundary relevant minimum ttc values decreased nonlinearly with postural challenge enabling prediction of stepping responses using quadratic equations when ttc calculations incorporated center of mass acceleration the quadratic fits were better and gave more accurate predictions of the ttc values that would trigger stepping responses in addition ttc minima occurred earlier with acceleration inclusion giving more advanced warning of perturbation severity our results were in agreement with ttc predictions based on hof s model and suggest that ttc may function as a control parameter influencing the postural control system s decision to transition from a stationary base of support to a stepping strategy

limits of recovery against slip induced falls while walking abstract slip induced falls in gait often have devastating consequences the purposes of this study were 1 to select the determinants that can best discriminate the outcomes recoveries or falls of an unannounced slip induced in gait and to find their corresponding threshold i e the limits of recovery which can clearly separate these two outcomes and 2 to verify these results in a subset of repeated slip trials based on the data collected from 69 young subjects during a slip induced in gait nine different ways of combining the center of mass com stability the hip height and its vertical velocity were investigated with the aid of logistic regression the results revealed that the com stability s and limb support represented by the quotient of hip vertical velocity to hip height s hip recorded at the instant immediately prior to the recovery step touchdown were sufficiently sensitive to account for all 100 variance in falls and specific enough to account for nearly all 98 3 variability in recoveries this boundary s hip 0 22 s 0 25 which quantifies the risk of falls in the stability limb support quotient s s hip domain was fully verified using second slip and third slip trials n 76 with classification of falls at 100 and recoveries at 98 6 the severity of an actual fall is likely to be greater further below the boundary while the likelihood of a fall diminishes above it finally the slope of the boundary also indicates the tradeoff between the stability and limb support whereby high stability can compensate for the insufficiency in limb support or vice versa

sensitivity of femoral strain calculations to anatomical scaling errors in musculoskeletal models of movement the determination of femoral strain in post menopausal women is important for studying bone fragility femoral strain can be calculated using a reference musculoskeletal model scaled to participant anatomies referred to as scaled generic combined with finite element models however anthropometric errors committed while scaling affect the calculation of femoral strains we assessed the sensitivity of femoral strain calculations to scaled generic anthropometric errors we obtained ct images of the pelves and femora of 10 healthy post menopausal women and collected gait data from each participant during six weight bearing tasks scaled generic musculoskeletal models were generated using skin mounted marker distances image based models were created by modifying the scaled generic models using muscle and joint parameters obtained from the ct data scaled generic and image based muscle and hip joint forces were determined by optimisation a finite element model of each femur was generated from the ct images and both image based and scaled generic principal strains were computed in 32 regions throughout the femur the intra participant regional rms error increased from 380 e r2 0 92 p 0 001 to 4064 e r2 0 48 p 0 001 representing 5 2 and 55 6 of the tensile yield strain in bone respectively the peak strain difference increased from 2821 e in the proximal region to 34 166 e at the distal end of the femur the inter participant rms error throughout the 32 femoral regions was 430 e r2 0 95 p 0 001 representing 5 9 of bone tensile yield strain we conclude that scaled generic models can be used for determining cohort based averages of femoral strain whereas image based models are better suited for calculating participant specific strains throughout the femur

non parametric wiener filter for reducing noise on reproducible pure signals this paper communicates a novel method of wiener filtering signals from scientific instruments to reduce their noise content the main prerequisite for the applicability of this technique is that the pure i e noiseless signal is reproducible a condition that is satisfied by a wide range of experimental measurements the benefits of this wiener filter design approach are its simplicity generality and practicality in particular signal dependent or multiplicative noise are accommodated without complication the non parametric filter does not require models of pure signal or noise statistics and is exactly optimal for the observed i e noisy signal ensemble implementation of this wiener filter only requires measurement of observed signal correlation functions after deriving the classical stationary signal wiener filter the analysis is extended to derive the reproducible stationary pure signal wiener filter a distinction is made between non adaptive wiener filters derived from correlations computed as ensemble averages and adaptive wiener filters derived from correlations computed as time averages the analysis is extended again to encapsulate non stationary signal ensembles and further extended to synthesize wiener filters based on statistically good observed signal correlation estimates for arbitrarily many pure signal reproductions

influence of body segment parameter estimation on calculated ground reaction forces in highly dynamic movements the effect of body segment parameter estimation bsp on the inverse dynamics modelling results has not yet been demonstrated in specific groups during athletic movements with high segment accelerations therefore the purpose of this study was to analyse this effect in ski jumpers as representatives of a specific group i e low body mass index by comparing calculated and measured ground reaction forces during ski jumping imitation jumps full body kinematics and vertical ground reaction forces were recorded of 9 ski jumpers performing three imitation jumps each bsp were estimated using three previously published one individually optimized and one ski jumper group specific model vertical ground reaction forces were calculated using the vertical acceleration of the segments as well as the bsp of the single models in a top down approach statistical analysis revealed a main model effect concerning the root mean square error between the calculated and the measured ground reaction force with deviations between the models of 53 individual optimization and the application of the ski jumper group specific model increased the accuracy of the calculated ground reaction forces by 11 and 7 respectively compared to the best performing published model the results of inverse dynamics modelling are very sensitive to the bsp estimation for specific groups like ski jumpers during movements incorporating high segment accelerations this emphasizes the importance of selecting adequate bsp estimation models or methods when analysing specific groups in highly dynamic movements in order to increase the accuracy of the inverse dynamics analyses results

validation of a functional method for the estimation of hip joint centre location the present study assesses the accuracy with which the subject specific coordinates of the hip joint centre hjc in a pelvic anatomical frame can be estimated using different methods the functional method was applied by calculating the centre of the best sphere described by the trajectory of markers placed on the thigh during several trials of hip rotations different prediction methods proposed in the literature and in the present investigation which estimate the hjc of adult subjects using regression equations and anthropometric measurements were also assessed the accuracy of each of the above mentioned methods was investigated by comparing their predictions with measurements obtained on a sample of 11 male adult able bodied volunteers using roentgen stereophotogrammetric analysis rsa assumed to provide the true hjc locations prediction methods estimated the hjc location at an average rms distance of 25 30 mm the functional method performed significantly better and estimated hjcs within a rms distance of 13 mm on average this result may be confidently generalised if the photogrammetric experiment is carefully conducted and an optimal analytical approach used the method is therefore suggested for use in motion analysis when the subject s hip range of motion is not limited in addition the facts that it is not an invasive technique and that it has relatively small and un biased errors make it suitable for regression equations identification with no limit to sample size and population typology

sloped muscle excitation waveforms improve the accuracy of forward dynamic simulations abstract mathematical models of the muscle excitation are useful in forward dynamic simulations of human movement tasks one objective was to demonstrate that sloped as opposed to rectangular excitation waveforms improve the accuracy of forward dynamic simulations a second objective was to demonstrate the differences in simulated muscle forces using sloped versus rectangular waveforms to fulfill these objectives surface emg signals from the triceps brachii and elbow joint angle were recorded and the intersegmental moment of the elbow joint was computed from 14 subjects who performed two cyclic elbow extension experiments at 200 and 300 deg s additionally the surface emg signals from the leg musculature joint angles and pedal forces were recorded and joint intersegmental moments were computed during a more complex pedaling task 90 rpm at 250 w using forward dynamic simulations four optimizations were performed in which the experimental intersegmental moment was tracked for the elbow extension tasks and four optimizations were performed in which the experimental pedal angle pedal forces and joint intersegmental moments were tracked for the pedaling task in these optimizations the three parameters onset and offset time and peak excitation defining the sloped triangular quadratic and hanning and rectangular excitation waveforms were varied to minimize the difference between the simulated and experimentally tracked quantities for the elbow extension task the intersegmental elbow moment root mean squared error onset timing error and offset timing error were less from simulations using a sloped excitation waveform compared to a rectangular excitation waveform p 0 001 the average and peak muscle forces were from 7 to 16 larger and 20 28 larger respectively when using a rectangular excitation waveform the tracking error for pedaling also decreased when using a sloped excitation waveform with the quadratic waveform generating the smallest tracking errors for both tasks these results support the use of sloped over rectangular excitation waveforms to establish greater confidence in the results of forward dynamic simulations

alterations in trunk bending stiffness following changes in stability and equilibrium demands of a load holding task abstract the contribution of the trunk neuromuscular system tns to spine stability has been shown in earlier studies by characterizing changes in antagonistic activity of trunk muscles following alterations in stability demands of a task whether and or how much such changes in the response of tns to alteration in stability demand of the task alter spinal stiffness remains unclear to address this research gap a repeated measure study was conducted on twenty gender balanced asymptomatic individuals to evaluate changes in trunk bending stiffness throughout the lumbar spine s range of flexion following alterations in both stability and equilibrium demands of a load holding task trunk bending stiffness was determined using trunk stiffness tests in upright posture on a rigid metal frame under different equilibrium and stability demands on the lower back increasing the stability demand by increasing the height of lifted load 30 cm only increased trunk bending stiffness 39 over the lower range of lumbar flexion and under the low equilibrium demand condition similarly increasing the equilibrium demand of the task by increasing the weight of lifted load by 3 5 kg only increased trunk bending stiffness 55 over the low range of lumbar flexion and under the low stability demand condition our results suggest a non linear relationship between changes in stability and equilibrium demands of a task and the contribution of tns to trunk bending stiffness specifically alterations in tns response to changes in stability and equilibrium demand of a given task will increase stiffness of the trunk only if the background stiffness is low

the score residual a quality index to assess the accuracy of joint estimations abstract the determination of an accurate centre of rotation cor from skin markers is essential for the assessment of abnormal gait patterns in clinical gait analysis despite the many functional approaches to estimate cors no non invasive analytical determination of the error in the reconstructed joint location is currently available the purpose of this study was therefore to verify the residual of the symmetrical centre of rotation estimation score as a reliable indirect measure of the error of the computed joint centre to evaluate the score residual numerical simulations were performed to evaluate cor estimations at different ranges of joint motion a statistical model was developed and used to determine the theoretical relationships among the score residual the magnitude of the skin marker artefact the corrections to the marker positions and the error of the cor estimations to the known centre of rotation we found that the equation err 0 5rs provides a reliable relationship among the cor error err and the scaled score residual rs providing that any skin marker artefact is first minimised using the optimal common shape technique ocst measurements on six healthy volunteers showed a reduction of score residual from 11 to below 6 mm and therefore demonstrated consistency of the theoretical considerations and numerical simulations with the in vivo data this study also demonstrates the significant benefit of the ocst for reducing skin marker artefact and thus for predicting the accuracy of determining joint centre positions in functional gait analysis for the first time this understanding of the score residual allows a measure of error in the non invasive assessment of joint centres this measure now enables a rapid assessment of the accuracy of the cor as well as an estimation of the reproducibility and repeatability of skeletal motion patterns

synergies in the ground reaction forces and moments during double support in curb negotiation in young and older adults abstract falls that occur while negotiating steps are a leading cause of death in older adults although recent efforts have improved understanding of the mechanics and control of stepping behaviors the double support phase during stepping is understudied therefore we quantified the stability of the resultant forces and moments acting on the body during this phase these quantities determine the movement of the body and therefore their stability is essential for successful stepping behavior we measured the ground reaction variables grvs under both feet as healthy young n 10 and older adults n 10 stepped up and down a curb we employed the uncontrolled manifold method to evaluate the hypotheses that the grvs covary to stabilize the resultant force and moment in the three coordinate directions robust stabilization of the resultant forces and moments was observed while stepping up however while stepping down the stability of the resultant moment was prioritized over that of the resultant forces in the vertical and the anterior posterior directions and the stability of the resultant medio lateral force was prioritized over that of the resultant anterior posterior force the salience of stabilizing whole body angular momentum and medio lateral motion during locomotion is well known but their prioritization during adaptive gait is a novel result and is possibly related to the higher likelihood of falling during descent versus ascent finally contrary to our expectations we observed no age differences in our stability indices indicating that healthy aging does not diminish the stability of the resultant forces and moments

subject specific regression equations to estimate lower spinal loads during symmetric and asymmetric static lifting abstract workplace safety assessment personalized treatment design and back pain prevention programs require accurate subject specific estimation of spinal loads since no noninvasive method can directly estimate spinal loads easy to use regression equations that are constructed based on the results of complex musculoskeletal models appear as viable alternatives thus we aim to develop subject specific regression equations of l4 l5 and l5 s1 shear and compression forces during various symmetric asymmetric tasks using a nonlinear personalized finite element musculoskeletal trunk model kinematics and electromyography emg activities of 19 young healthy subjects were collected during 64 different symmetric asymmetric tasks to investigate the reliability and accuracy of the musculoskeletal model and regression equations we compared estimated trunk muscle activities and l4 l5 intradiscal pressures idps respectively with our own electromyography data emgs and reported in vivo pressure measurements although in general six independent rotation components three trunk t11 rotations and three pelvic s1 rotations are required to determine kinematics along the spine only two surrogate variables trunk flexion and its asymmetric angles satisfactorily predicted all six rotation components r2 0 94 regression equations developed based on subject specific inputs predicted spinal loads in satisfactory agreement with idp measurements r2 0 85 predicted muscle activities in the personalized musculoskeletal models were in moderate to weak agreements with our measured emgs in 19 participants based on dominance analysis trunk flexion and its asymmetry angle hand load weight hand load lever arm and body weight were the most important variables while the effects of body height and sex on spinal loads remained small

zero vs one dimensional parametric vs non parametric and confidence interval vs hypothesis testing procedures in one dimensional biomechanical trajectory analysis biomechanical processes are often manifested as one dimensional 1d trajectories it has been shown that 1d confidence intervals cis are biased when based on 0d statistical procedures and the non parametric 1d bootstrap ci has emerged in the biomechanics literature as a viable solution the primary purpose of this paper was to clarify that for 1d biomechanics datasets the distinction between 0d and 1d methods is much more important than the distinction between parametric and non parametric procedures a secondary purpose was to demonstrate that a parametric equivalent to the 1d bootstrap exists in the form of a random field theory rft correction for multiple comparisons to emphasize these points we analyzed six datasets consisting of force and kinematic trajectories in one sample paired two sample and regression designs results showed first that the 1d bootstrap and other 1d non parametric cis were qualitatively identical to rft cis and all were very different from 0d cis second 1d parametric and 1d non parametric hypothesis testing results were qualitatively identical for all six datasets last we highlight the limitations of 1d cis by demonstrating that they are complex design dependent and thus non generalizable these results suggest that i analyses of 1d data based on 0d models of randomness are generally biased unless one explicitly identifies 0d variables before the experiment and ii parametric and non parametric 1d hypothesis testing provide an unambiguous framework for analysis when one s hypothesis explicitly or implicitly pertains to whole 1d trajectories

approximate saturated and blurred self affinity of random processes with finite domain power law power spectrum we study the approximate self affine regimes of random processes with finite domain power law power spectra for arbitrary values of the spectral exponent in particular we focus on regimes that are imprinted in the structure function of the process for this function we obtain exact series and asymptotic expansions we also provide expressions for the usual statistical parameters variance correlation time and introduce a specific parameter called chronothesy which measures the intensity of the self affine fluctuations there are essentially three qualitatively different self affine regimes corresponding to values of in the following intervals 1 3 the process shows again approximate self affinity which with increasing saturates and leads to a self affinity exponent of 2 for 0 1 the approximate self affine behavior which in this case is characterized by a negative exponent is blurred by intense oscillations to the extent that in practice it cannot be observed as an application it is shown that the time series generated by sampling x and y coordinates of the lorenz system are characterized by blurred self affinity

generalization of treadmill perturbation to overground slip during gait effect of different perturbation distances on slip recovery treadmill perturbation training tm training may improve a person s fall resistance whereby adjusting slip distance can be a simple way to manipulate training intensity the purpose of this study was to determine the effects of different slip distances in tm training 12 cm vs 18 cm on its generalization to the recovery from a novel free slip during overground walking generalization here means the ability to apply learned skill from tm training to slip recovery during overground walking thirty six young adults in the tm 12 or the tm 18 group underwent either a 12 cm or an 18 cm slip during the treadmill walking for seven times or in the control group were not exposed to any perturbation their responses were also contrasted with previously reported results from overground perturbation training og training in which participants received either a 12 cm or an 18 cm slip during level walking with the same number of repetitions everyone was then exposed to the same generalization test during a novel free slip in overground walking their proactive and reactive control of stability was measured and compared tm training displayed a significant training effect in comparison to the control group p 0 05 these results underscore the further needs to investigate the potential of the treadmill as a convenient instrument that can effectively deliver perturbation training

array processing in correlated noise fields based on instrumental variables and subspace fitting accurate signal parameter estimation from sensor array data is a problem which has received much attention in the last decade a number of parametric estimation techniques have been proposed in the literature in general these methods require knowledge of the sensor to sensor correlation of the noise which constitutes a significant drawback this difficulty can be overcome only by introducing alternative assumptions that enable separating the signals from the noise in some applications the raw sensor outputs can be preprocessed so that the emitter signals are temporally correlated with correlation length longer than that of the noise an instrumental variable iv approach can then be used for estimating the signal parameters without knowledge of the spatial color of the noise a computationally simple iv approach has recently been proposed by the authors herein a refined technique that can give significantly better performance is derived a statistical analysis of the parameter estimates is performed enabling optimal selection of certain user specified quantities a lower bound on the attainable error variance is also presented the proposed optimal iv method is shown to attain the bound if the signals have a quasideterministic character

breaststroke swimmers moderate internal work increases toward the highest stroke frequencies a model to predict the mechanical internal work of breaststroke swimming was designed it allowed us to explore the frequency internal work relationship in aquatic locomotion its accuracy was checked against internal work values calculated from kinematic sequences of eight participants swimming at three different self chosen paces model predictions closely matched experimental data 0 58 0 07 vs 0 59 0 05 j kg 1 m 1 t 23 0 30 p 0 77 which was reflected in a slope of the major axis regression between measured and predicted total internal work whose 95 confidence intervals included the value of 1 0 84 0 61 1 07 n 24 the model shed light on swimmers ability to moderate the increase in internal work at high stroke frequencies this strategy of energy minimization has never been observed before in humans but is present in quadrupedal and octopedal animal locomotion this was achieved through a reduced angular excursion of the heaviest segments 7 2 2 9 and 3 6 1 5 for the thighs and trunk respectively p 0 05 in favor of the lightest ones 8 8 2 3 and 7 4 1 0 for the shanks and forearms respectively p 0 05 a deeper understanding of the energy flow between the body segments and the environment is required to ascertain the possible dependency between internal and external work this will prove essential to better understand swimming mechanical cost determinants and power generation in aquatic movements

in vivo estimation of the glenohumeral joint centre by functional methods accuracy and repeatability assessment abstract several algorithms have been proposed for determining the centre of rotation of ball joints these algorithms are used rather to locate the hip joint centre few studies have focused on the determination of the glenohumeral joint centre however no studies have assessed the accuracy and repeatability of functional methods for glenohumeral joint centre this paper aims at evaluating the accuracy and the repeatability with which the glenohumeral joint rotation centre ghrc can be estimated in vivo by functional methods the reference joint centre is the glenohumeral anatomical centre obtained by medical imaging five functional methods were tested the algorithm of gamage and lasenby 2002 bias compensated halvorsen 2003 symmetrical centre of rotation estimation ehrig et al 2006 normalization method chang and pollard 2007 helical axis woltring et al 1985 the glenohumeral anatomical centre ghac was deduced from the fitting of the humeral head four subjects performed three cycles of three different movements flexion extension abduction adduction and circumduction for each test the location of the glenohumeral joint centre was estimated by the five methods analyses focused on the 3d location on the repeatability of location and on the accuracy by computing the euclidian distance between the estimated ghrc and the ghac for all the methods the error repeatability was inferior to 8 25 mm this study showed that there are significant differences between the five functional methods the smallest distance between the estimated joint centre and the centre of the humeral head was obtained with the method of gamage and lasenby 2002

can stability really predict an impending slip related fall among older adults the primary purpose of this study was to systematically evaluate and compare the predictive power of falls for a battery of stability indices obtained during normal walking among community dwelling older adults one hundred and eighty seven community dwelling older adults participated in the study after walking regularly for 20 strides on a walkway participants were subjected to an unannounced slip during gait under the protection of a safety harness full body kinematics and kinetics were monitored during walking using a motion capture system synchronized with force plates stability variables including feasible stability region measurement margin of stability the maximum floquet multiplier the lyapunov exponents short and long term and the variability of gait parameters including the step length step width and step time were calculated for each subject sensitivity of predicting slip outcome fall vs recovery was examined for each stability variable using logistic regression results showed that the feasible stability region measurement predicted fall incidence among these subjects with the highest sensitivity 68 4 except for the step width with an sensitivity of 60 2 no other stability variables could differentiate fallers from those who did not fall for the sample included in this study the findings from the present study could provide guidance to identify individuals at increased risk of falling using the feasible stability region measurement or variability of the step width

mechanical demand and multijoint control during landing depend on orientation of the body segments relative to the reaction force the purpose of this study was to determine how diverse momentum conditions and anatomical orientation at contact influences mechanical loading and multijoint control of the reaction force during landings male collegiate gymnasts n 6 performed competition style landings n 3 of drop jumps front saltos and back saltos from a platform 0 72 m onto landing mats 0 12 m kinematics 200 fps reaction forces 800 hz and muscle activation patterns surface emg 1600 hz of seven lower extremity muscles were collected simultaneously between task differences in segment orientation relative to the reaction force contributed to significant between task differences in knee and hip net joint moments njm during the impact phase during the stabilization phase ankle knee and hip njms acted to control joint flexion between task differences in muscle activation patterns indicated that gymnasts scaled biarticular muscle activation to accommodate for between task differences in njm after contact activation of muscles on both sides of the joint suggests that impedance like control was used to stabilize the joints and satisfy the mechanical demand imposed on the lower extremity between subject differences in the set of muscles used to control total body center of mass tbcm trajectory and achieve lower extremity njms suggests that control of multijoint movements involving impact needs to incorporate mechanical objectives at both the total body and local level the functional consequences of such a control structure may prove to be an asset to gymnasts particularly when required to perform a variety of landing tasks under a variety of environmental constraints

estimation numerique de la vitesse de decroissance des spectres de puissance numerical estimation of the fall off rates of spectral densities les signaux ayant des spectres de puissance dont la decroissance est en ont traditionnellement vu leur exposant estime par une regression lineaire sur un graphique log log un probleme methodologique survient lorsque le spectre de puissance du signal possede des zeros cela introduit en effet des poles dans la representation log log rendant toute regression au niveau du spectre tres perilleuse nous presentons une methode qui permet d eviter ces valeurs extremes en ne faisant au niveau de la representation log log qu une regression sur un sous ensemble choisi de maxima locaux d autre part il est bien connu que la dimension fractale de fonctions de holder d exposant auto affines est ce qui permet en particulier de pouvoir juger de la qualite d une estimation obtenue par la methode precedente pour la dimension fractale de la fonction introduite par kieswetter le comportement de la methode est analyse a partir du spectre de puissance de fonctions lisses sans que le resultat estime ne puisse etre utilise pour obtenir la dimension fractale du signal qui n est pas auto affine finalement nous examinons les limitations des methodes d analyse spectrale pour l estimation d une vitesse de decroissance algebrique signals with spectral densities have traditionally had the exponent estimated by linear regression on a log log plot this is problematic when the spectrum of the signal crosses zero because this introduces poles in the log plot of the spectrum we present a method which avoids these extreme values namely doing a regression on a subset of local maxima on the same log log plot self affine functions with holder exponent are well known to have the fractal dimension and we thus estimate the fractal dimension of the function introduced by kieswetter on smooth functions the new method is tested on log log representation of power spectra but no relation can be established with the fractal dimension of the signal due to lack of self affinity the limitations of spectral analysis methods for estimation of algebraic fall off rates are discussed

effect of low pass filtering on joint moments from inverse dynamics implications for injury prevention analyses of joint moments are important in the study of human motion and are crucial for our understanding of e g how and why acl injuries occur such analyses may be affected by artifacts due to inconsistencies in the equations of motion when force and movement data are filtered with different cut off frequencies the purpose of this study was to quantify the effect of these artifacts and compare joint moments calculated with the same or different cut off frequency for the filtering of force and movement data 123 elite handball players performed sidestep cutting while the movement was recorded by eight 240 hz cameras and the ground reaction forces were recorded by a 960 hz force plate knee and hip joint moments were calculated through inverse dynamics with four different combinations of cut off frequencies for signal filtering movement 10 hz force 10 hz 10 10 movement 15 hz force 15 hz movement 10 hz force 50 hz 10 50 movement 15 hz force 50 hz the results revealed significant differences especially between conditions with different filtering of force and movement mean sd peak knee abduction moment for the 10 10 and 10 50 condition were 1 27 0 53 and 1 64 0 68 nm kg respectively ranking of players based on knee abduction moments were affected by filtering condition out of 20 players with peak knee abduction moment higher than mean 1 sd with the 10 50 condition only 11 were still above mean 1 sd when the 10 10 condition was applied hip moments were very sensitive to filtering cut off mean sd peak hip flexion moment was 3 64 0 75 and 5 92 1 80 under the 10 10 and 10 50 conditions respectively based on these findings force and movement data should be processed with the same filter conclusions from previous inverse dynamics studies where this was not the case should be treated with caution

adjustments to mcconville et al and young et al body segment inertial parameters body segment inertial parameters bsips are important data in biomechanics they are usually estimated from predictive equations reported in the literature however most of the predictive equations are ambiguously applicable in the conventional 3d segment coordinate systems scss also the predictive equations reported in the literature all include two assumptions the centre of mass and the proximal and distal endpoints are assumed to be aligned and the inertia tensor is assumed to be principal in the segment axes these predictive equations restraining both position of the centre of mass and orientation of the principal axes of inertia become restrictive when computing 3d inverse dynamics when analyzing the influence of bsip estimations on joint forces and moments and when evaluating personalized 3d bsips obtained from medical imaging in the current study the extensive data from mcconville et al 1980 anthropometric relationships of body and body segment moments of inertia afamrl tr 80 119 aerospace medical research laboratory wright patterson air force base dayton ohio and from young et al 1983 anthropometric and mass distribution characteristics of the adults female technical report afamrl tr 80 119 faa civil aeromedical institute oklaoma city oklaoma are adjusted in order to correspond to joint centres and to conventional segment axes in this way scaling equations are obtained for both males and females that provide bsips which are directly applicable in the conventional scss and do not restrain the position of the centre of mass and the orientation of the principal axes these adjusted scaling equations may be useful for researchers who wish to use appropriate 3d bsips for posture and movement analysis

segment interaction analysis of the stance limb in sprint running a high angular velocity of the thigh of the stance limb generated by hip extensor musculature is commonly thought to be a performance determining factor in sprint running however the thigh segment is a component of a linked system i e the lower limb therefore it is unlikely that the kinematics of the thigh will be due exclusively to the resultant joint moment rjm at the hip the purpose of this study was to quantify by means of segment interaction analysis the determinants of sagittal plane kinematics of the lower limb segments during the stance phase of sprint running video and ground reaction force data were collected from four male athletes performing maximal effort sprints the analysis revealed that during the first third of the stance phase a hip extension moment was the major determinant of the increasing angular velocity of the thigh however during the mid third of stance hip and knee extension moments and segment interaction effects all contributed to the thigh attaining its peak angular velocity extension moments at the ankle and to a lesser extent the knee were attributed with preventing the collapse of the shank under the effects of the interactive moment due to ground reaction force the angular acceleration of the foot was determined almost completely by the rjm at the ankle and the interactive moment due to ground reaction force further research is required to determine if similar results exit for a wide range of athletes and for other stages of a sprint race e g early acceleration maximal velocity and deceleration phases

bias compensated least squares estimate of the center of rotation abstract it is shown that a recently published least squares method for the estimation of the average center of rotation is biased consequently a correction term is proposed and an iterative algorithm is derived for finding a bias compensated solution to the least squares problem the accuracy of the proposed bias compensated least squares method is compared to the previously proposed least squares method by monte carlo simulations the tests show that the new method gives a substantial improvement in accuracy

body segment inertial parameters and low back load in individuals with central adiposity abstract there is a paucity of information regarding the impact of central adiposity on the inertial characteristics of body segments deriving low back loads during lifting requires accurate estimate of inertial parameters the purpose was to determine the body segment inertial parameters of people with central adiposity using a photogrammetric technique and then to evaluate the impact on lumbar spine loading five participants with central adiposity waist hip ratio 0 9 waist circumference 102 cm were compared to a normal bmi group a 3d wireframe model of the surface topography was constructed partitioned into 8 body segments and then body segment inertial parameters were calculated using volumetric integration assuming uniform segment densities for the segments central adiposity dependent increases in body segment parameters ranged from 12 to 400 varying across segments greatest for trunk and parameters the increase in mass distribution to the trunk was accompanied by an anterior and inferior shift of the centre of mass a proximal shift in centre of mass was detected for the extremities along with a reduction in mass distribution to the lower extremity l5 s1 torques 392 vs 263 nm and compressive forces 5918 vs 3986 n were substantially elevated in comparison to the normal bmi group as well as in comparison to torques and forces predicted using published bsip equations central adiposity resulted in substantial but non uniform increases in inertial parameters resulting in task specific increases in torque and compressive loads arising from different inertial and physical components

a novel approach to study human posture control principal movements obtained from a principal component analysis of kinematic marker data human upright posture is maintained by postural movements which can be quantified by principal movements pms obtained through a principal component analysis pca of kinematic marker data the current study expands the concept of principal movements in analogy to newton s mechanics by defining principal position pp principal velocity pv and principal acceleration pa and demonstrates that a linear combination of pps and pas determines the center of pressure cop variance in upright standing twenty one subjects equipped with 27 markers distributed over all body segments stood on a force plate while their postural movements were recorded using a standard motion tracking system a pca calculated on normalized and weighted posture vectors yielded the pps and their time derivatives the pvs and pas cop variance explained by the pps and pas was obtained through a regression analysis the first 15 pms quantified 99 3 of the postural variance and explained 99 60 0 22 mean sd of the anterior posterior and 98 82 0 74 of the lateral cop variance in the 21 subjects calculation of the pms thus provides a data driven definition of variables that simultaneously quantify the state of the postural system pps and pvs and the activity of the neuro muscular controller pas since the definition of pps and pas is consistent with newton s mechanics these variables facilitate studying how mechanical variables such as the cop motion are governed by the postural control system

the simulation of aerial movement ii a mathematical inertia model of the human body a mathematical inertia model which permits the determination of personalized segmental inertia parameter values from anthropometric measurements is described the human body is modelled using 40 geometric solids which are specified by 95 anthropometric measurements a stadium solid is introduced for modelling the torso segments using perimeter and width measurements this procedure is more accurate than the use of elliptical discs of given width and depth and permits a smaller number of such solids to be used inertia parameter values may be obtained for body models of up to 20 segments errors in total body mass estimates from this and other models are discussed with reference to the unknown lung volumes

non driving intersegmental knee moments in cycling computed using a model that includes three dimensional kinematics of the shank foot and the effect of simplifying assumptions assessing the importance of non driving intersegmental knee moments i e varus valgus and internal external axial moments on over use knee injuries in cycling requires the use of a three dimensional 3 d model to compute these loads the objectives of this study were 1 to develop a complete 3 d model of the lower limb to calculate the 3 d knee loads during pedaling for a sample of the competitive cycling population and 2 to examine the effects of simplifying assumptions on the calculations of the non driving knee moments the non driving knee moments were computed using a complete 3 d model that allowed three rotational degrees of freedom at the knee joint included the 3 d inertial loads of the shank foot and computed knee loads in a shank fixed coordinate system all input data which included the 3 d segment kinematics and the six pedal load components were collected from the right limb of 15 competitive cyclists while pedaling at 225 w and 90 rpm on average the peak varus and internal axial moments of 7 8 and 1 5 n m respectively occurred during the power stroke whereas the peak valgus and external axial moments of 8 1 and 2 5 n m respectively occurred during the recovery stroke however the non driving knee moments were highly variable between subjects the coefficients of variability in the peak values ranged from 38 7 to 72 6 when it was assumed that the inertial loads of the shank foot for motion out of the sagittal plane were zero the root mean squared difference rmsd in the non driving knee moments relative to those for the complete model was 12 of the peak varus valgus moment and 25 of the peak axial moment when it was also assumed that the knee joint was revolute with the flexion extension axis perpendicular to the sagittal plane the rmsd increased to 24 of the peak varus valgus moment and 204 of the peak axial moment thus the 3 d orientation of the shank segment has a major affect on the computation of the non driving knee moments while the inertial contributions to these loads for motions out of the sagittal plane are less important

the generic modeling fallacy average biomechanical models often produce non average results computational biomechanics models constructed using nominal or average input parameters are often assumed to produce average results that are representative of a target population of interest to investigate this assumption a stochastic monte carlo analysis of two common biomechanical models was conducted consistent discrepancies were found between the behavior of average models and the average behavior of the population from which the average models input parameters were derived more interestingly broadly distributed sets of non average input parameters were found to produce average or near average model behaviors in other words average models did not produce average results and models that did produce average results possessed non average input parameters these findings have implications on the prevalent practice of employing average input parameters in computational models to facilitate further discussion on the topic the authors have termed this phenomenon the generic modeling fallacy the mathematical explanation of the generic modeling fallacy is presented and suggestions for avoiding it are provided analytical and empirical examples of the generic modeling fallacy are also given

computation of trunk equilibrium and stability in free flexion extension movements at different velocities velocity of movement has been suggested as a risk factor for low back disorders the effect of changes in velocity during unconstrained flexion extension movements on muscle activations spinal loads base reaction forces and system stability was computed in vivo measurements of kinematics and ground reaction forces were initially carried out on young asymptomatic subjects the collected kinematics of three subjects representing maximum mean and minimum lumbar rotations were subsequently used in the kinematics driven model to compute results during the entire movements at three different velocities estimated spinal loads and muscle forces were significantly larger in fastest pace as compared to slower ones indicating the effect of inertial forces spinal stability was improved in larger trunk flexion angles and fastest movement partial or full flexion relaxation of global extensor muscles occurred only in slower movements some local lumbar muscles especially in subjects with larger lumbar flexion and at slower paces also demonstrated flexion relaxation results confirmed the crucial role of movement velocity on spinal biomechanics predictions also demonstrated the important role on response of the magnitude of peak lumbar rotation and its temporal variation

predicted threshold against backward balance loss following a slip in gait the purpose of this study was to use a 7 link moment actuated human model to predict at liftoff of the trailing foot in gait the threshold of the center of mass com velocity relative to the base of support bos required to prevent backward balance loss during single stance recovery from a slip five dynamic optimization problems were solved to find the minimum com velocities that would allow the simulation to terminate with the com above the bos when the com started 0 25 0 5 0 75 1 0 and 1 25 foot lengths behind the heel of the stance foot i e behind the bos the initial joint angles of the model were based on averaged data from experimental trials foot ground contact was modeled using 16 visco elastic springs distributed under the stance foot slipping was modeled by setting the sliding coefficient of friction of these springs to 0 02 the forward velocity of the com necessary to avoid a backward balance loss is nearly two times larger under slip conditions under non slip conditions the predicted threshold for backward balance loss following a slip agreed well with experimental data collected from 99 young adults in response to 927 slips during walking in all trials in which a subject s com had a velocity below the predicted threshold the subject s recovery foot landed posterior to the slipping foot as predicted finally combining experimental data with optimization we verified that the 7 link model could more accurately predict gait stability than a 2 link model

body segment inertial parameter estimation for the general population of older adults the practical determination of accurate body segment inertial parameters for the general older adult population remains a problem especially in estimating these parameters for women and accounting for variations in body type a method is presented for determining the mass and center of mass location of the body segments of individuals within the general population of older adults effects of sex and body type on older adult mass distribution are accounted for using 32 easily obtainable body measurements the method is based on existing results from different data sources and employs a combination of validated estimation approaches including body mass and segment length proportions linear and nonlinear regression equations and a mathematical model of the trunk the method was applied to a validation sample of healthy community dwelling older adults 29 men 50 women predicted body mass was 96 7 4 8 and 95 7 3 7 of measured body mass in the men and women respectively the estimates of body segment mass and trunk center of mass location for the sample population approximate those reported in the literature supporting the validity of the described method by producing practical subject specific estimates of body segment inertial parameters the method should allow more accurate biomechanical analyses of the older adult population

predictive regression modeling of body segment parameters using individual based anthropometric measurements abstract body segment parameters such as segment mass center of mass and radius of gyration are used as inputs in static and dynamic ergonomic and biomechanical models used to predict joint and muscle forces and to assess risks of musculoskeletal injury previous work has predicted body segment parameters bsps in the general population using age and obesity levels as statistical predictors merrill et al 2017 estimated errors in the prediction of bsps can be as large as 40 depending on age and the prediction method employed durkin and dowling 2003 thus more accurate and representative segment parameter inputs are required for attempting to predict modeling outputs such as joint contact forces muscle forces and injury risk in individuals this study aims to provide statistical models for predicting torso thigh shank upper arm and forearm segment parameters in working adults using whole body dual energy x ray absorptiometry dxa scan data along with a set of anthropometric measurements the statistical models were developed on a training data set and independently validated on a separate test data set the predicted bsps in validation data were on average within 5 of the actual in vivo dxa based bsps while previously developed predictions de leva 1996 had average errors of up to 60 indicating that the new models greatly increase the accuracy in predicting segment parameters these final developed models can be used for calculating representative bsps in individuals for use in modeling applications dependent on these parameters