Video-based Motion Analysis System Research Articles

Prediction of gait kinetics using Markerless-driven musculoskeletal modeling

Video-based motion analysis systems are emerging in the biomechanics research community, yet there is limited exploration of kinetics prediction using RGB-markerless kinematics and musculoskeletal modeling. This project aimed to provide ground reaction force (GRF) and ground reaction moment (GRM) predictions during over-ground gait by introducing RGB-markerless kinematics into a musculoskeletal modeling framework. Full-body markerless kinematic inputs and musculoskeletal modeling were used to obtain GRF and GRM predictions which were compared to measured force plate values. The markerless-driven predictions yielded average root mean-squared error (RMSE) in the stance phase of 0.035 ± 0.009 N∙BW−1, 0.070 ± 0.014 N∙BW−1, and 0.155 ± 0.041 N∙BW−1 in the mediolateral (ML), anteroposterior (AP), and vertical (V) GRFs. This was accompanied by moderate to high correlations and interclass correlation coefficients (ICC) indicating moderate to good agreement between measured and predicted values (95% Confidence Inervals: ML = [0.479, 0.717], AP = [0.714, 0.856], V = [0.803, 0.905]). For ground reaction moments (GRM), average RMSE was 0.029 ± 0.013 Nm∙BWH-1, 0.014 ± 0.005 Nm∙BWH-1, and 0.005 ± 0.002 Nm∙BWH-1 in the sagittal, frontal, and transverse planes. Pearson correlations and ICCs indicated poor agreement between systems for GRMs (95% Confidence Intervals: Sagittal = [0.314, 0.608], Frontal = [0.006, 0.373], Transverse = [0.269, 0.570]). Currently, RMSE is larger than target thresholds set from studies using Kinect, inertial, or marker-based kinematic drivers; but methodological considerations highlighted in this work may help guide follow-up iterations. At this point, further use in research or clinical practice is cautioned until methodological considerations are addressed, although results are promising at this point.

P30: Remote and In-Clinic Teletracking and Analysis for Enhanced Rheumatologic Examination

Purpose: Rheumatoid arthritis and related arthritides associated with chronic joint inflammation of the hands significantly affects range of motion and daily living functionality due to stiffness, pain, and swelling. It is vital to closely monitor changes in joint flexibility across the progression of this disease state to assess treatment efficacy and provide informed quantitative analysis. Our group previously developed and reported on a video-based motion analysis system with a wide range of utility. Using this system, we evaluated the range of motion of radiocarpal and phalangeal joints in arthritic versus normal subjects. We hypothesized that use of this system in clinic and at home would provide accurate and quantitative data on joint flexibility and also allow assessment of progression of flexibility of affected joints in patients experiencing joint inflammation across their treatment timelines. Methods: Healthy volunteers and those experiencing self-reported, clinically-diagnosed arthritis were instructed via a telehealth remote platform to place small brightly-colored visual markers (1cm2) on their hands. Using our video motion analysis system, video recordings were captured as subjects performed: 1) wrist flexion and extension, 2) finger flexion and extension, and 3) finger adduction and abduction. The digital recordings were imaged as a motion signature and the data was analyzed to obtain the angle (degrees) of rotation about the joints by correcting full extension/adduction to a “zero degrees” baseline and calculating the degrees of flexion/abduction at the peak point. This protocol allowed for versatility of analysis based on the treatment course providing novel access to patient monitoring outside of the clinic setting. Results: Range of motion of the radiocarpal and phalangeal joints measured in degrees was successfully recorded on both healthy (n=14, 9F 5M) and arthritic subjects (n=8, 4M 4F) in a virtual setting via the video motion analysis system. In all cases the system offered the resolution required to determine overall joint flexibility. A clear quantitative distinction was detected between arthritic patients versus health subjects. Conclusion: A video motion analysis system utilizing small markers can characterize, track, and compare joint flexibility in at-home settings for rheumatoid arthritis and related joint diseases. With face-to-face clinic time being an increasingly limited commodity, this system offers a valuable, digital tool to not only assess patients remotely but it adds a quantitative dimension previously absent in the Rheumatologic exam. As this project continues, arthritis subjects will be monitored over time to assess functionality of disease-state tracking across a treatment time course. Digital assessment of joint flexibility is a useful addition to the diagnostic armamentarium of the Rheumatologist, Orthopedist and related Health Care providers enhancing the precision of diagnosis and therapy.

Detection of Carotid Artery Stenosis Based on Video Motion Analysis for Fast Screening.

BackgroundCarotid artery stenosis (CAS) is a common cause of ischemic stroke, and the early detection of CAS may improve patient outcomes. Carotid Doppler ultrasound is commonly used to diagnose CAS. However, it is costly and may not be practical for regular screening practice. This article presents a novel noninvasive and noncontact detection technique using video‐based motion analysis (VMA) to extract useful information from subtle pulses on the skin surface to screen for CAS.Methods and ResultsWe prospectively enrolled 202 patients with prior carotid Doppler ultrasound data. A short 30‐second video clip of the neck was taken using a commercial mobile device and analyzed by VMA with mathematical quantification of the amplitude of skin motion changes in a blinded manner. The first 40 subjects were used to set up the VMA protocol and define cutoff values, and the following 162 subjects were used for validation. Overall, 54% of the 202 subjects had ultrasound‐confirmed CAS. Using receiver operating characteristic curve analysis, the area under the curve of VMA‐derived discrepancy values to differentiate patients with and without CAS was excellent (area under the curve, 0.914 [95% CI, 0.874–0.954]; P<0.01). The best cutoff value of VMA‐derived discrepancy values to screen for CAS was 5.1, with a sensitivity of 87% and a specificity of 87%. The diagnostic accuracy was consistently high in different subject subgroups.ConclusionsA simple and accurate screening technique to quickly screen for CAS using a VMA system is feasible, with acceptable sensitivity and specificity.

Kinematic differences between national and college level weightlifters during snatch technique

The aim of this study is to assess the suitability of a micro-processing unit of motion analysis (MPUMA), for monitoring, reproducing, and tracking upper limb movements. The MPUMA is based on an inertial measurement unit, a 16-bit digital signal controller and a customized algorithm. To validate the performance of the system, simultaneous recordings of the angular trajectory were performed with a video-based motion analysis system. A test of the flexo-extension of the shoulder joint during the active elevation in a complete range of 120º of the upper limb was carried out in 10 healthy volunteers. Additional tests were carried out to assess MPUMA performance during upper limb tracking. The first, a 3D motion reconstruction of three movements of the shoulder joint (flexo-extension, abduction–adduction, horizontal internal–external rotation), and the second, an upper limb tracking online during the execution of three movements of the shoulder joint followed by a continuous random movement without any restrictions by using a virtual model and a mechatronic device of the shoulder joint. Experimental results demonstrated that the MPUMA measured joint angles that are close to those from a motion-capture system with orientation RMS errors less than 3º.

Influence of pelvic inclination on sit to stand task in stroke patients

BackgroundStroke results in an impaired sit to stand (STS) task. Pelvic movements are essential in daily living activities. Few studies investigated the effect of spine and pelvis separately on functional activities in stroke patients.ObjectiveThe study aimed to assess the angles of pelvic inclination (anterior and posterior pelvic tilt angles) (APT and PPT) during sitting position and during STS movement. It aimed also to determine the influence of sagittal pelvic tilt angles on STS performance in stroke patients.Patients and methodsThirty male hemi-paretic stroke patients (GI) and 15 matched healthy volunteer subjects (GII) represented the sample of this study. Stroke patients were assigned into two equal groups (group Ia and Ib). Sagittal pelvic tilt angles were measured by using the palpation meter inclinometer during sitting position and during initiation and mid of STS by using two dimensional (2D) video-based motion analysis system. Time of five repetitions STS test was used to assess the ability to perform STS task.ResultsThe results showed a significant increase of PPT angle during static sitting, a significant decrease in APT angle during initiation and mid of STS task and a significant increase in time taken for five repetitions STS test in both stroke groups (P < 0.05).ConclusionAbnormal pelvic alignment and movements affect the functional performance of stroke patients during sitting and sit to stand task.Trial registrationNCT03053154. Registered January 22, 2017. Retrospectively registered.

Validity of the microsoft kinect system in assessment of compensatory stepping behavior during standing and treadmill walking

BackgroundRapid compensatory stepping plays an important role in preventing falls when balance is lost; however, these responses cannot be accurately quantified in the clinic. The Microsoft Kinect™ system provides real-time anatomical landmark position data in three dimensions (3D), which may bridge this gap.MethodsCompensatory stepping reactions were evoked in 8 young adults by a sudden platform horizontal motion on which the subject stood or walked on a treadmill. The movements were recorded with both a 3D-APAS motion capture and Microsoft Kinect™ systems. The outcome measures consisted of compensatory step times (milliseconds) and length (centimeters). The average values of two standing and walking trials for Microsoft Kinect™ and the 3D-APAS systems were compared using t-test, Pearson’s correlation, Altman-bland plots, and the average difference of root mean square error (RMSE) of joint position.ResultsThe Microsoft Kinect™ had high correlations for the compensatory step times (r = 0.75–0.78, p = 0.04) during standing and moderate correlations for walking (r = 0.53–0.63, p = 0.05). The step length, however had a very high correlations for both standing and walking (r > 0.97, p = 0.01). The RMSE showed acceptable differences during the perturbation trials with smallest relative error in anterior-posterior direction (2-3%) and the highest in the vertical direction (11–13%). No systematic bias were evident in the Bland and Altman graphs.ConclusionsThe Microsoft Kinect™ system provides comparable data to a video-based 3D motion analysis system when assessing step length and less accurate but still clinically acceptable for step times during balance recovery when balance is lost and fall is initiated.

Evaluation of suitability of a micro-processing unit of motion analysis for upper limb tracking

The aim of this study is to assess the suitability of a micro-processing unit of motion analysis (MPUMA), for monitoring, reproducing, and tracking upper limb movements. The MPUMA is based on an inertial measurement unit, a 16-bit digital signal controller and a customized algorithm. To validate the performance of the system, simultaneous recordings of the angular trajectory were performed with a video-based motion analysis system. A test of the flexo-extension of the shoulder joint during the active elevation in a complete range of 120º of the upper limb was carried out in 10 healthy volunteers. Additional tests were carried out to assess MPUMA performance during upper limb tracking. The first, a 3D motion reconstruction of three movements of the shoulder joint (flexo-extension, abduction–adduction, horizontal internal–external rotation), and the second, an upper limb tracking online during the execution of three movements of the shoulder joint followed by a continuous random movement without any restrictions by using a virtual model and a mechatronic device of the shoulder joint. Experimental results demonstrated that the MPUMA measured joint angles that are close to those from a motion-capture system with orientation RMS errors less than 3º.

The influence of a powered knee-ankle-foot orthosis on walking in poliomyelitis subjects: A pilot study.

Traditionally, the anatomical knee joint is locked in extension when walking with a conventional knee-ankle-foot orthosis. A powered knee-ankle-foot orthosis was developed to provide restriction of knee flexion during stance phase and active flexion and extension of the knee during swing phase of gait. The purpose of this study was to determine differences of the powered knee-ankle-foot orthosis compared to a locked knee-ankle-foot orthosis in kinematic data and temporospatial parameters during ambulation. Quasi-experimental design. Subjects with poliomyelitis (n = 7) volunteered for this study and undertook gait analysis with both the powered and the conventional knee-ankle-foot orthoses. Three trials per orthosis were collected while each subject walked along a 6-m walkway using a calibrated six-camera three-dimensional video-based motion analysis system. Walking with the powered knee-ankle-foot orthosis resulted in a significant reduction in both walking speed and step length (both 18%), but a significant increase in stance phase percentage compared to walking with the conventional knee-ankle-foot orthosis. Cadence was not significantly different between the two test conditions (p = 0.751). There was significantly higher knee flexion during swing phase and increased hip hiking when using the powered orthosis. The new powered orthosis permitted improved knee joint kinematic for knee-ankle-foot orthosis users while providing knee support in stance and active knee motion in swing in the gait cycle. Therefore, the new powered orthosis provided more natural knee flexion during swing for orthosis users compared to the locked knee-ankle-foot orthosis. This orthosis has the potential to improve knee joint kinematics and gait pattern in poliomyelitis subjects during walking activities.

Optimising filtering parameters for a 3D motion analysis system

In the analysis of movement data it is common practice to use a low-pass filter in order to reduce measurement noise. However, the choice of a cut-off frequency is typically rather arbitrary. The aim of the present study was to evaluate a new method to find the optimal cut-off frequency for filtering kinematic data. In particular, we propose to use rigid marker clusters to determine the dynamic precision of a given 3D motion analysis system, and to use this precision as criterion to find the optimal cut-off frequency for filtering the data. We tested this method using a model-based approach in a situation in which measurement noise is a serious concern, namely the registration of the kinematics of swimming using a video-based motion analysis system. For the model data we found that filtering the data with a single cutoff frequency of 6Hz under some conditions decreased the accuracy of the reconstruction of the kinematics compared to using the unfiltered data. If the cut-off frequency was used that yielded optimal dynamic precision, then the accuracy improved by 29% compared to using raw data irrespective of the cluster position, close to the optimal accuracy improvement of 30%. We confirmed in an experiment that the cut-off frequency at which optimal precision was found varied between cluster positions and subjects, similar to the results obtained with the model. We conclude that 3D motion analysis systems can be made more accurate by optimising the cut-off frequency used in filtering the data with regard to their precision. Furthermore, the dynamic precision method seems useful to evaluate the effect of various filtering procedures.

The effects of pressurized partial pressure suits on operational ergonomics

A study on capstan partial pressure suits (PPSs) was conducted to determine their effects on pilots' operational performance on a series of ergonomic measures at different pressure levels using objective and subjective approaches. Tests of range of motion, operational performance and operational strength were carried out on ten male subjects wearing PPSs under 6 different pressure conditions. Subjective tests related to pressure tolerance and operational performance were also conducted. A video-based motion capture and analysis system was used to record the trajectories of body motions. Analysis of variance was used to test the effects of the different pressures. It was concluded that a pressurized PPS had a significant impact on the pilot's range of motion (ROM) and operational performance, but no significant effect on their operational strength. Range of motion and operational performance decreased as pressure increased, but they were affected differently. The results may provide mission planners, suit designers and human factors engineers with better insight into the understanding of pilots' operational function, mobility and strength capabilities when wearing pressurized PPS. Relevance to industryThis paper presents pilots' range of motion, operational performance and operational strength with pressurized PPS dressed and can help mission planners, suit designers and human factors engineers to improve PPS' performance.

Distinguishing the causes of falls in humans using an array of wearable tri-axial accelerometers

Falls are the number one cause of injury in older adults. Lack of objective evidence on the cause and circumstances of falls is often a barrier to effective prevention strategies. Previous studies have established the ability of wearable miniature inertial sensors (accelerometers and gyroscopes) to automatically detect falls, for the purpose of delivering medical assistance. In the current study, we extend the applications of this technology, by developing and evaluating the accuracy of wearable sensor systems for determining the cause of falls. Twelve young adults participated in experimental trials involving falls due to seven causes: slips, trips, fainting, and incorrect shifting/transfer of body weight while sitting down, standing up from sitting, reaching and turning. Features (means and variances) of acceleration data acquired from four tri-axial accelerometers during the falling trials were input to a linear discriminant analysis technique. Data from an array of three sensors (left ankle+right ankle+sternum) provided at least 83% sensitivity and 89% specificity in classifying falls due to slips, trips, and incorrect shift of body weight during sitting, reaching and turning. Classification of falls due to fainting and incorrect shift during rising was less successful across all sensor combinations. Furthermore, similar classification accuracy was observed with data from wearable sensors and a video-based motion analysis system. These results establish a basis for the development of sensor-based fall monitoring systems that provide information on the cause and circumstances of falls, to direct fall prevention strategies at a patient or population level.

High knee valgus in female subjects does not yield higher knee translations during drop landings: A biplane fluoroscopic study

The goal of this study was to determine the effects of peak knee valgus angle and peak knee abductor moment on the anterior, medial, and lateral tibial translations (ATT, MTT, LTT) in the "at risk" female knee during drop landing. Fifteen female subjects performed drop landings from 40 cm. Three-dimension knee motion was simultaneously recorded using a high speed, biplane fluoroscopy system, and a video-based motion analysis system. Valgus knee angles and knee abduction moments were stratified into low, intermediate, and high groups and peak ATT, MTT, and LTT were compared between these groups with ANOVA (α = 0.05). Significant differences were observed between stratified groups in peak knee valgus angle (p < 0.0001) and peak knee abduction moment (p < 0.0001). However, no corresponding differences in peak ATT, LTT, and MTT between groups exhibiting low to high-peak knee valgus angles (ATT: p = 0.80; LTT: p = 0.25; MTT: p = 0.72); or, in peak ATT (p = 0.61), LTT (p = 0.26) and MTT (p = 0.96) translations when stratified according to low to high knee abduction moments, were found. We conclude that the healthy female knee is tightly regulated with regard to translations even when motion analysis derived knee valgus angles and abduction moments are high.

A study of the reproducibility of the marker application of the Cleveland Clinic Marker Set including the Plug-In Gait Upper Body Model in clinical gait analysis

The aim of this study is to assess the suitability of a micro-processing unit of motion analysis (MPUMA), for monitoring, reproducing, and tracking upper limb movements. The MPUMA is based on an inertial measurement unit, a 16-bit digital signal controller and a customized algorithm. To validate the performance of the system, simultaneous recordings of the angular trajectory were performed with a video-based motion analysis system. A test of the flexo-extension of the shoulder joint during the active elevation in a complete range of 120º of the upper limb was carried out in 10 healthy volunteers. Additional tests were carried out to assess MPUMA performance during upper limb tracking. The first, a 3D motion reconstruction of three movements of the shoulder joint (flexo-extension, abduction–adduction, horizontal internal–external rotation), and the second, an upper limb tracking online during the execution of three movements of the shoulder joint followed by a continuous random movement without any restrictions by using a virtual model and a mechatronic device of the shoulder joint. Experimental results demonstrated that the MPUMA measured joint angles that are close to those from a motion-capture system with orientation RMS errors less than 3º.

Comparison of Center of Mass Displacement and Velocity Error of Artistic Gymnastic Movements Measured with Different Anthropometric Approaches

The main purpose of this study was to compare the deviation of human segment center of gravity displacement and velocity in different models of human body segment parameters through video analysis. All human movements in our study were videotaped by JVC camera (60 Hz) and analyzed through the APAS video-based motion analysis system for seven different human segment models. The collected kinematic parameters (center of gravity displacement and velocity) were analyzed by using dependent sample t test and the estimated standard errors to examine the difference of seven segment models. The results showed that Dempster model, Clauser model, Zatsiorsky model had significant (p＜.05) difference in the displacement and the velocity with the individual segments of model. Furthermore, those three models had greater standard error in the displacement and velocity. The individual segment model has smaller standard error compared to Cheng CT model, Ho MRI model and Cheng MRI model. These results suggest that future studies engaged in male artistic gymnasts should apply male gymnast segment model to analyze or apply Cheng CT model, Ho MRI model and Cheng MRI model, if gymnast segment model was not available.

Active Upper Limb Prosthesis Based on Natural Movement Trajectories

The motion of the current prostheses is sequential and does not allow natural movements. In this work, complex natural motion patterns from a healthy upper limb were characterized in order to be emulated for a trans-humeral prosthesis with three degrees of freedom at the elbow. Firstly, it was necessary to define the prosthesis workspace, which means to establish a relationship using an artificial neural network (ANN), between the arm-forearm (3-D) angles allowed by the prosthesis, and its actuators length. The 3-D angles were measured between the forearm and each axis of the reference system attached at the elbow. Secondly, five activities of daily living (ADLs) were analyzed by means of the elbow flexion (EF), the forearm prono-supination (FPS) and the 3-D angles, from healthy subjects, by using a video-based motion analysis system. The 3-D angles were fed to the prosthesis model (ANN) in order to analyze which ADLs could be emulated by the prosthesis. As a result, a prosthesis kinematics approximation was obtained. In conclusion, in spite of the innovative mechanical configuration of the actuators, it was possible to carry out only three of the five ADLs considered. Future work will include improvement of the mechanical configuration of the prosthesis to have greater range of motion.

Case study evaluation of body weight-supported treadmill training for parkinsonian gait

Parkinsonian gait is characterized by kinetic and kinematic anomalies such as reduced push-off and reduced walking velocity. It is evident that any improvement to gait is likely to result in concomitant improvement in aspects of everyday life that require whole body ambulation. Consequently, the aim of this study was to quantify, biomechanically, the potential of body weight-supported treadmill training (BWSTT) in eliciting a shift toward a more normal pattern of gait for individuals with Parkinson's disease. A single-subject intervention-based research design was adopted. Kinetic, kinematic and spatiotemporal data were captured via the simultaneous use of a Kistler force platform and an automated video-based motion analysis system. The emphasis of the BWSTT intervention was to provide stimulus to the extensor load receptors of the lower extremities through the unloading and reloading of body weight, characterized through kinetic and kinematic profiles (Dietz, 1997). The findings of the study revealed significant enhancement—relative to ‘normal’ gait—of parkinsonian gait following BWSTT, which was reflected in observed normalization across measured spatiotemporal, kinematic, and kinetic parameters. As such, BWSTT may be a viable method of implementing sustained improvement to parkinsonian gait, although further large-scale research is needed.

The feasibility of a video-based motion analysis system in measuring the segmental movements between upper and lower cervical spine

The evaluation of the range of motion (ROM) and static posture in the cervical spine are important in physical examination. Despite offering dynamic assessment without radiation, the video-based motion analysis system has not yet been applied to measure the cervical segmental movements. The purposes of this study were to develop a neck model to differentiate the movements and posture between upper and lower cervical spine, and to examine the reliability of measuring cervical motion with surface markers and the aid of videofluoroscopy. Sixteen healthy adult subjects (eight males and eight females) participated in this study. Ten surface markers were used to estimate the discrepancies in cervical vertebral angles compared with corresponding bony landmarks throughout the ROM. The average intraclass correlation coefficients (ICCs) of the paired vertebral angles between surface markers and bony landmarks ranged from 0.844 to 0.975 and the mean absolute difference (MAD) averaged 2.96°. Our results indicate high consistency between surface markers and bony landmarks throughout the cervical movements. The mean upper (C0–C2) and lower (C2–C7) cervical joint angles in the neutral position were 18.59 ± 4.33° and 23.98 ± 6.15°, respectively. Furthermore, the reliability of the digitizing procedure within raters (ICC = 0.850–0.999; MAD = 0.58–2.42°) and between raters (ICC = 0.759–0.988; MAD = 0.59–2.66°) suggests that the neck motion analysis model is a feasible method for investigating static neck posture or dynamic motion between upper and lower cervical spine.

In Vitro Assessment of a Motion-Based Optimization Method for Locating the Talocrural and Subtalar Joint Axes

The locations of the joint axes of the ankle complex vary considerably between subjects, yet no noninvasive method with demonstrated accuracy exists for locating these axes. The moments of muscle and ground reaction forces about the joint axes are dependent on axis locations, making knowledge of these locations critical to accurate musculoskeletal modeling of the foot and ankle. The accuracy of a computational optimization method that fits a two-revolute model to measured motion was assessed using computer-generated data, a two-revolute mechanical linkage, and three lower-leg cadaver specimens. Motions were applied to cadaver specimens under axial load while bone-mounted markers attached to the tibia, talus, and calcaneus were tracked using a video-based motion analysis system. Estimates of the talocrural and subtalar axis locations were computed from motions of the calcaneus relative to the tibia using the optimization method. These axes were compared to mean helical axes computed directly from tibia, talus, and calcaneus motions. The optimization method performed well when the motions were computer-generated or measured in the mechanical linkage, with angular differences between optimization and mean helical axes ranging from 1 deg to 5 deg. In the cadaver specimens, however, these differences exceeded 20 deg. Optimization methods that locate the anatomical joint axes of the ankle complex by fitting two revolute joints to measured tibia-calcaneus motions may be limited because of problems arising from non-revolute behavior.

Reduced Hip Extension in the Elderly: Dynamic or Postural?

Lee LW, Zavarei K, Evans J, Lelas JJ, Riley PO, Kerrigan DC. Reduced hip extension in the elderly: dynamic or postural? Objective To test the hypothesis that reduced hip extension and increased anterior pelvic tilt in the elderly are dynamic gait phenomena that do not occur during normal standing posture. Design Experimental. Setting Gait laboratory. Participants Twenty-five older adult subjects (mean age ± standard deviation, 71±5y) and 25 young adult subjects (mean age, 26±5y). Intervention Subjects were observed during standing and walking at self-determined comfortable, slow, and fast walking speeds. Positions and kinematics of the pelvis and lower extremities were measured using a 3-dimensional video-based motion analysis system. Main Outcome Measures Peak hip extension and anterior pelvic tilt. Results There were no statistically significant differences between the older and young adult groups during standing with respect to either hip extension (3°±5° vs 1°±6°) or anterior pelvic tilt (11°±5° vs 10°±5°). On the other hand, at comfortable walking speeds, the older adult group had reduced peak hip extension (7°±6° vs 11°±6°, P<.05) and increased anterior pelvic tilt (15°±5° vs 11°±5°) compared with the young adult group. At fast walking speeds, peak hip extension was significantly reduced in the older adult group than in the young adult group (9°±6° vs 14°±6°, P<.05), but there was no significant difference at slow walking speeds (6°±6° vs 9°±5°). Conclusions Age-related changes in gait defined by reduced peak hip extension and increased pelvic tilt are dynamic rather than standing postural characteristics.

Effects of environmental and job-task factors on workers' gait characteristics on slippery surfaces

The objective of this study was to investigate the kinetic and kinematic aspects of slips associated with gait on a slippery surface under various environmental and job-task risk factors. Forty healthy industrial workers (age: 40.3 ± 14.9 years) participated in the study. Using a strain gauge type force platform and a video-based motion analysis system, kinetic and kinematic measurements of the subjects' foot movements were obtained. Of all gait trials, there were 1558 slips (60.9%). Slips were likely to occur when subjects were negotiating a turning path and an oily surface. Greater anterior-posterior center of pressure (CP) excursion and maximum required coefficient of friction (RCOF) were found for oily surfaces compared to dry surfaces. Subjects changed their gait patterns by shortening their stride length, slowing walking speed, and decreasing heel contact angle in the poorly lit and slippery environment. Significant correlations were found between slip occurrence and anterior-posterior CP excursion, mean RCOF, sliding distance and sliding velocity, but not the coefficient of friction (COF) of shoes. In addition to good housekeeping and proper selection of floor materials and safety shoes, slip and fall prevention should include proper workers' training in dealing with risk factors of slips and falls in the workplace.