Coefficient Of Multiple Correlation Values Research Articles

Correlation between soil erodibility and light penetrometer blows: A case study in Sungai Langat, Malaysia

The soil erodibility (K) factor is one of the key parameters used for predicting and estimating soil erosion in models such as Universal Soil Loss Equation (USLE) and Modified Universal Soil Loss Equation (RUSLE). It is the inherent resistance of soil to survive erosion and reflects the susceptibility of soil to the erosion process. Long-term studies for direct measurement of K factor are time-consuming and expensive, so efforts were made by the researchers to develop simple indices to relate soil properties with K factor for instant and economical estimation of erodibility. Mackintosh Probe is a portable and lightweight dynamic penetrometer that provides a relatively fast, economical, and easy assessment of subsoil. In this study, soil samples were collected from the Sungai Langat site, and a series of laboratory tests, including sieve analysis, hydrometer analysis, and organic matter content, were performed. K factor was determined by employing Wischmeier and Tew equations. The mean values of the K factor for the Sungai Langat site were found to be 0.005 and 0.0045 for Tew and Wischmeier equations, respectively. Multiple regression analysis was performed to analyze the relations between Mackintosh Probe and K factor, which the coefficient of multiple correlation values of 0.345 and 0.352 for the Tew and Wischmeier equation, respectively. Although the analysis represented a weak relation between Mackintosh Probe values and K factor, however, it provides a basis for the research perspective to simplify the estimation of soil erodibility with a minimalistic experimental setup.

Moving outside the lab: Markerless motion capture accurately quantifies sagittal plane kinematics during the vertical jump

Markerless motion capture using deep learning approaches have potential to revolutionize the field of biomechanics by allowing researchers to collect data outside of the laboratory environment, yet there remain questions regarding the accuracy and ease of use of these approaches. The purpose of this study was to apply a markerless motion capture approach to extract lower limb angles in the sagittal plane during the vertical jump and to evaluate agreement between the custom trained model and gold standard motion capture. We performed this study using a large open source data set (N = 84) that included synchronized commercial video and gold standard motion capture. We split these data into a training set for model development (n = 69) and test set to evaluate capture performance relative to gold standard motion capture using coefficient of multiple correlations (CMC) (n = 15). We found very strong agreement between the custom trained markerless approach and marker-based motion capture within the test set across the entire movement (CMC > 0.991, RMSE < 3.22°), with at least strong CMC values across all trials for the hip (0.853 ± 0.23), knee (0.963 ± 0.471), and ankle (0.970 ± 0.055). The strong agreement between markerless and marker-based motion capture provides evidence that markerless motion capture is a viable tool to extend data collection to outside of the laboratory. As biomechanical research struggles with representative sampling practices, markerless motion capture has potential to transform biomechanical research away from traditional laboratory settings into venues convenient to populations that are under sampled without sacrificing measurement fidelity.

Validity of inertial sensor based 3D joint kinematics of static and dynamic sport and physiotherapy specific movements.

3D joint kinematics can provide important information about the quality of movements. Optical motion capture systems (OMC) are considered the gold standard in motion analysis. However, in recent years, inertial measurement units (IMU) have become a promising alternative. The aim of this study was to validate IMU-based 3D joint kinematics of the lower extremities during different movements. Twenty-eight healthy subjects participated in this study. They performed bilateral squats (SQ), single-leg squats (SLS) and countermovement jumps (CMJ). The IMU kinematics was calculated using a recently-described sensor-fusion algorithm. A marker based OMC system served as a reference. Only the technical error based on algorithm performance was considered, incorporating OMC data for the calibration, initialization, and a biomechanical model. To evaluate the validity of IMU-based 3D joint kinematics, root mean squared error (RMSE), range of motion error (ROME), Bland-Altman (BA) analysis as well as the coefficient of multiple correlation (CMC) were calculated. The evaluation was twofold. First, the IMU data was compared to OMC data based on marker clusters; and, second based on skin markers attached to anatomical landmarks. The first evaluation revealed means for RMSE and ROME for all joints and tasks below 3°. The more dynamic task, CMJ, revealed error measures approximately 1° higher than the remaining tasks. Mean CMC values ranged from 0.77 to 1 over all joint angles and all tasks. The second evaluation showed an increase in the RMSE of 2.28°– 2.58° on average for all joints and tasks. Hip flexion revealed the highest average RMSE in all tasks (4.87°– 8.27°). The present study revealed a valid IMU-based approach for the measurement of 3D joint kinematics in functional movements of varying demands. The high validity of the results encourages further development and the extension of the present approach into clinical settings.

Comparative Study of Kinematics and Muscle Activity Between Elite and Amateur Table Tennis Players During Topspin Loop Against Backspin Movements.

This study investigated differences of lower limb kinematics and muscle activity during table tennis topspin loop against backspin movements between elite players (EPs) and amateur players (APs). Ten EPs and ten APs performed crosscourt backhand loop movements against the backspin ball with maximal power. Vicon motion analysis and a MEGA ME6000 system was used to capture kinematics and surface EMG data. The motion was divided into two phases, including the backswing and swing. The joints’ flexion and extension angle tendency between EPs and APs differed significantly. The coefficient of multiple correlation (CMC) values for EPs were all beyond 0.9, indicating high similarity of joint angles change. APs presented moderate similarity with CMC values from 0.5 to 0.75. Compared to APs, EPs presented larger ankle eversion, knee and hip flexion at the beginning moment of the backswing. In the sEMG test, EPs presented smaller standardized AEMG (average electromyography) of the lower limb muscles in the rectus femoris and tibia anterior on both sides. Additionally, the maximum activation of each muscle for EPs was smaller and MPF (mean power frequency) of the lower limb was greater during the whole movement. The present study revealed that EPs could complete this technical motion more economically than APs, meanwhile, EPs were more efficient in muscle usage and showed better balance ability.

Reliability and Repeatability of Countermovement Jump Waveforms

Though the countermovement vertical jump (CMJ) has traditionally been used to assess lower body force and power, the force-time characteristics of the CMJ ground reaction force (GRF) waveform may be of value in predicting injury risk and assessing training readiness. Prior to evaluating the CMJ GRF waveform as a diagnostic and evaluative tool, the reliability of the waveform on a within and between day basis should be established. PURPOSE: To determine the within day and between day reliability of the CMJ GRF waveform in healthy individuals. METHODS: Twenty-five healthy (age = 21.5 ± 1.9 years), recreationally active men and women completed one familiarization and three experimental visits, a minimum of 48 hours apart. Each visit consisted of a brief, standardized warmup, two submaximal CMJs, and three maximal CMJs performed on a force plate (sample rate = 1000Hz). Each jump was separated by two minutes. To reduce the variability associated with arm swing, all jumps were performed with subjects’ hands on their hips. The CMJ GRF waveform for each jump, beginning with the minimum GRF during the counter-movement and ending at take off, was interpolated and re-sampled to a uniform length of 1000 data points. Individual within and between day reliabilities for each subject’s waveform shapes were calculated using the adjusted coefficient of multiple determination (R2a) as previously described by Kadaba et al (J Orthop Res, 7(6): 849-860, 1989). Briefly, the primary calculation of the within day reliability compared the GRF at each data point of a single jump with the mean GRF for that day at the corresponding data point. The between day reliability was calculated similarly, however, the mean GRF at each point for each day was compared to the mean GRF at that point of all three days. Data is reported as the coefficient of multiple correlation (CMC), the positive square root of the R2a. RESULTS: The CMJ waveforms were highly reliable, both on a within day (0.968 ± 0.020) and between day (0.962 ± 0.018) basis. Observed within day CMC values ranged from 0.909 – 0.993, whereas between day CMC values ranged from 0.917 – 0.994. CONCLUSION: Individual CMJ GRF waveforms are highly reliable under these test conditions. These results provide preliminary evidence that the CMJ GRF waveforms shapes may have utility as a diagnostic and evaluative tool.

COMPARISON OF AN ELECTROMAGNETIC AND OPTICAL SYSTEM DURING DYNAMIC MOTION

Few studies have concurrently investigated the accuracy and repeatability of an optical and electromagnetic (EM) system during dynamic motion. The purposes of this study were to: (1) assess the accuracy of both an EM and optical system when compared to a gold standard and (2) to compare the intra- and inter-day repeatability during 3D kinematic motion of both systems. The gold standard used for accuracy assessment was a robot programmed to manipulate a carbon fiber beam through pre-defined motions within the capture volume of both systems at 30, 45 and 60°/s. A total of 12 healthy young adults were tested for intra- and inter-day repeatability of hip, knee and ankle joint angles during a sit-to-stand movement. Marker trajectories were captured using an 8-camera Motion Analysis system and a Polhemus Liberty system. Optical markers for both portions of the study were precisely marked to allow for digitization by the EM system, with collections taken at 120 Hz. Accuracy and repeatability were assessed using the RMS error and coefficient of multiple correlations (CMC), respectively. The optical system demonstrated a 1–2.5° lower RMS error in tracking the robot movements in the transverse and sagittal planes when compared to the EM system. However, it was possible that metal interference affected the accuracy of the EM system. High intra-day and inter-day repeatability was demonstrated by both systems during the sit-to-stand task. The optical system did demonstrate slightly higher CMC values for between day trials, though skin motion artifact might have affected the EM system to a greater extent. Overall, both systems demonstrated an adequate ability to track dynamic motion.

Assessment of three-dimensional joint kinematics of the upper limb during simulated swimming using wearable inertial-magnetic measurement units

ABSTRACTThe analysis of the joint kinematics during swimming plays a fundamental role both in sports conditioning and in clinical contexts. Contrary to the traditional video analysis, wearable inertial-magnetic measurements units (IMMUs) allow to analyse both the underwater and aerial phases of the swimming stroke over the whole length of the swimming pool. Furthermore, the rapid calibration and short data processing required by IMMUs provide coaches and athletes with an immediate feedback on swimming kinematics during training. This study aimed to develop a protocol to assess the three-dimensional kinematics of the upper limbs during swimming using IMMUs. Kinematics were evaluated during simulated dry-land swimming trials performed in the laboratory by eight swimmers. A stereo-photogrammetric system was used as the gold standard. The results showed high coefficient of multiple correlation (CMC) values, with median (first–third quartile) of 0.97 (0.93–0.95) and 0.99 (0.97–0.99) for simulated front-crawl and breaststroke, respectively. Furthermore, the joint angles were estimated with an accuracy increasing from distal to proximal joints, with wrist indices showing median CMC values always higher than 0.90. The present findings represent an important step towards the practical use of technology based on IMMUs for the kinematic analysis of swimming in applied contexts.

Movement Repeatability During Landing Following Anterior Cruciate Ligament Reconstruction

As many as 200,000 anterior cruciate ligament (ACL) injuries are diagnosed annually in the United States with 94% of these patients undergoing ACL reconstruction (ACLR). While ACLR and subsequent rehabilitation allow athletes to return to sports, they have a 15 fold increased risk of secondary ACL injuries. Discrete kinematic and kinetic asymmetries have been identified as secondary injury risk factors. PURPOSE: Determine the differences in sagittal plane knee angle and moment curves as well as the vertical ground reaction force (vGRF) curves between and within the surgical (S) and non-surgical (NS) limbs during landing six months following ACLR. METHODS: Three-dimensional motion capture was used to collect bilateral kinematic and kinetic data during 5 stop-jump trials on 20 adolescent patients (Age: 15.8±1.2 years) 6 months following ACLR. Patients were excluded if they had a previous ACLR, required additional surgical intervention, or were unable to complete the jumping assessment. Bilateral knee kinematic and kinetic as well as vGRF landing (initial contact - toe-off) ensemble curves were used for analysis. A coefficient of multiple correlation (CMC) was calculated between the S and NS side for each trial and were then averaged across trials to determine the symmetry CMC. In addition, the between trial CMC was calculated for both the S and the NS side for each patient. RESULTS: The between-limb symmetry was high for each variable (knee angle: 0.96 (range: 0.87-0.99), knee moment: 0.85 (range: 0.61-0.96), and vGRF: 0.73 (range: 0.38-0.95)), however, the repeatability appeared to be subject specific. The within-limb CMC for the NS side was higher (knee angle: 0.97 (range: 0.90 - 0.99), knee moment: 0.92 (range: 0.84-0.97), vGRF: 0.88 (range: 0.74-0.95)) than the within-limb CMC for the S side (knee angle: 0.96 (range: 0.87 - 0.99), knee moment: 0.90 (range: 0.81-0.97), vGRF: 0.86 (range: 0.74-0.93)). CONCLUSIONS: The landing patterns are highly repeatable across trials for all subjects on both limbs. However, the movement pattern asymmetries appear to be subject specific based on the range of CMC values reported. A subject specific analysis of symmetry could improve the understanding of movement quality and could be used in combination with discrete symmetry analysis to better understand secondary ACL injury risk.

Validation of a method to predict hammer speed from cable force

PurposeThe purpose of this study was to develop and validate a method that would facilitate immediate feedback on linear hammer speed during training. MethodsThree-dimensional hammer head positional data were measured and used to calculate linear speed (calculated speed) and cable force. These data were used to develop two linear regression models (shifted and non-shifted) that would allow prediction of hammer speed from measured cable force data (predicted speed). The accuracy of the two models was assessed by comparing the predicted and calculated speeds. Averages of the coefficient of multiple correlation (CMC) and the root mean square (RMS) of the difference between the predicted and calculated speeds for each throw of each participant were used to assess the level of accuracy of the predicted speeds. ResultsBoth regression models had high CMC values (0.96 and 0.97) and relatively low RMS values (1.27 m/s and 1.05 m/s) for the non-shifted and shifted models, respectively. In addition, the average percentage differences between the predicted and calculated speeds were 6.6% and 4.7% for the non-shifted and shifted models, respectively. The RMS differences between release speeds attained via the two regression models and those attained via three-dimensional positional data were also computed. The RMS differences between the predicted and calculated release speeds were 0.69 m/s and 0.46 m/s for the non-shifted and shifted models, respectively. ConclusionThis study successfully derived and validated a method that allows prediction of linear hammer speed from directly measured cable force data. Two linear regression models were developed and it was found that either model would be capable of predicting accurate speeds. However, data predicted using the shifted regression model were more accurate.

A thorough analysis of the coefficient of multiple correlation (Cmc) shows multiple problems

Introduction: The question of reliability is essential for any measurement method, and when investigating reliability of 3DGA kinematic curves the coefficient of multiple correlations (CMC) [1] is frequently used, despite the reports of methodological issues [2]. Theaimof the current studywas toperformasystematic evaluation of theCMCusing stochastic simulations. The results are exemplified on an inter-rater reliability study of 3DGA data related to marker placement. Patients/materials and methods: Synthetic gait curves were generated from a stochastic model where amplitude, vertical offset and a possible horizontal shift due to random error and timing issues were included as stochastic variables. The model was used hierarchically. First a “true” curve for each subject was sampled; then curves from each of the different test situations, e.g. different tester teams, was sampled using this “true” curve as the mean. The CMC is a measure of similarity of waveforms, e.g. curve data [1], comparing multiple curves from several subjects across test situations, e.g. testers. The CMC was calculated based on the synthetic data with systematic variations in curve amplitude, frequency, vertical curve offset, and number of subjects and number of test situations. Confidence intervals were estimated using bootstrapping. Seven healthy adult volunteers gave written informed consent to take part in the accompanying inter-rater reliability study. The subjects were tested on two consecutive days by two different tester teams. 3DGA data was recorded during bare feet, level walking along a 10m walkway at self-selected comfortable walking speed, using six Vicon MX13 cameras, and the PluginGait model. For each subject, one left cycle from each test situation was selected, based on similarity in walking speed. Results: Joints with large amplitudes, i.e. above 15◦, resulted in CMC>0.9. High sampling frequencies, i.e. above 20 points per gait cycle, also resulted in CMC>0.9. Increasing offsets resulted in decreasing CMC values. For two test situations 20 subjects resulted inwider CIs for the CMC than five subjects on five test situations. In the inter-rater reliability study, the CMC calculations consistently broke down, i.e. could not be computed, for jointswith a lowamplitude. In curves with a visually apparent systematic vertical offset, the CMC was still approximately 0.9. Discussion and conclusions: The CMC is sensitive to the amplitude of the curve, demonstrating how the signal-to-noise ratio is a problem issue. As the CMC does not adjust for the inter-gait-curve correlation between data points, higher sample frequency leads to high CMCs, merely due to high correlation between data in the calculations. The frequently used reliability design of two tester teams was demonstrated to show comparably high CIs. In conclusion, in our study the CMC did not show the statistical properties that are needed for it to be an overall measurement of curve similarity. Other methods than the CMC must be used to assess reliability of 3DGA data. References

Does tester experience influence the reliability with which 3D gait kinematics are collected in healthy adults?

ObjectivesTo determine whether tester experience influences the reliability of three-dimensional gait collections. DesignReliability study. ParticipantsTen healthy subjects visited a university gait laboratory on two separate days and underwent a walking gait analysis. During each visit, kinematic data were collected by a biomechanist with 8 years of 3D gait analysis experience (EXP) and a physical therapist with no previous 3D gait analysis experience (NOV). Main outcome measuresJoint kinematic angles were calculated using either a functional or predictive joint identification method. Within-tester and between-tester measures of reliability were determined by calculating the root mean square error (RMS) and coefficient of multiple correlations (CMC). ResultsWithin-tester RMS and CMC values were not significantly different (P > 0.05) between the EXP and NOV testers using either a functional or predictive joint approach. Within-tester CMC values exceeded 0.90 for both testers across all kinematic variables. Between-tester CMC reliability values were greater than 0.85 for all variables measured. ConclusionsFollowing basic training, a physiotherapy clinician with no previous 3D gait experience is as reliable as an experienced gait biomechanist with respect to marker placement accuracy. In addition, reliability comparisons between an experienced and novice tester appear independent of the joint identification method chosen.

Concurrent validation of Xsens MVN measurement of lower limb joint angular kinematics

This study aims to validate a commercially available inertial sensor based motion capture system, Xsens MVN BIOMECH using its native protocols, against a camera-based motion capture system for the measurement of joint angular kinematics. Performance was evaluated by comparing waveform similarity using range of motion, mean error and a new formulation of the coefficient of multiple correlation (CMC). Three dimensional joint angles of the lower limbs were determined for ten healthy subjects while they performed three daily activities: level walking, stair ascent, and stair descent. Under all three walking conditions, the Xsens system most accurately determined the flexion/extension joint angle (CMC > 0.96) for all joints. The joint angle measurements associated with the other two joint axes had lower correlation including complex CMC values. The poor correlation in the other two joint axes is most likely due to differences in the anatomical frame definition of limb segments used by the Xsens and Optotrak systems. Implementation of a protocol to align these two systems is necessary when comparing joint angle waveforms measured by the Xsens and other motion capture systems.

Interrater Reproducibility of Knee Movement Analyses during the Stance Phase: Use of Anatomical Landmark Calibration with a Rigid Marker Set

Objective. Measurements of knee joint movement in gait analysis may result in large errors caused by misplacement of reflective markers by the testers. To properly understand the measurement results, it is important to guarantee the reliability of the measurement method used for the purpose. The aim of this study was to confirm the interrater reproducibility of a measurement method with a rigid marker set (RMS). Methods. The study subjects were four healthy adults, and the testers were three physical therapists. The interrater reproducibility of the measurements was verified by using the coefficient of multiple correlations (CMCs) and the standard error of measurement (SEM). Results. The average CMCs values of 4 subjects in knee joint movement at the stance phase were greater than 0.8, and the average SEM values of 4 subjects in knee joint movement at the stance phase were also relatively good (maximum error: 2.42°). Conclusion. Based on these results, the measurement method with estimation of anatomical landmarks using the RMS can prevent misplacement during attachment of the reflective markers, as long as the testers have sufficient experience in attaching reflective markers.

Dynamic Clinical Assessment of Femoral Acetabular Impingement

Objectives:There has been a recent interest in the non-arthritic hip and its associated complex pathologies. Passive range of motion and static specialty tests are the corner stone of diagnosis and assessment of treatment. Little information exists on the use of dynamic functional measurements to assess non-arthritic hip function. The aims of this study were: (1) to measure and identify objective and reliable functional parameters to assess dynamic hip function, and (2) to compare functional kinematic and kinetic parameters among healthy controls and subjects with symptomatic diagnosed femoral acetabular impingement (FAI).Methods:An ongoing cross-sectional study was conducted on male healthy non-arthritic control and symptomatic, diagnosed FAI subjects. Functional kinematic and kinetic data were acquired with dynamic 3D motion analysis during stair ascent, stair descent, and a sit-to-stand maneuver. Joint kinematics were measured in degrees and joint kinetic moments were normalized by body mass (N-m/kg). Surface electromyographic (EMG) activity was measured for hip and trunk musculature. Measurement reliability was quantified with the adjusted coefficient of multiple correlation (CMC), and was calculated for angle, moment and EMG per subject, and averaged across subjects. Control and FAI subjects were compared with differences in kinematic and kinetic waveforms.Results:Data from ten healthy subjects (Age=25±4 years; BMI=24.3±3.6); and six FAI subjects (Age=32±10 years; BMI=25±4) have been recorded. Control and FAI subject CMC values are listed in Table 1. Kinematic and kinetic behavior differed (>1 SD) between control and FAI for multiple joints and planes of motion. Increased internal hip rotation moments were recorded in FAI subjects during both stair ascent and descent tasks, as compared to healthy controls. Increased external rotation moments were recorded in FAI subjects during the sit-to-stand task. Electromyographic data demonstrated notable differences (>1 SD) between healthy and FAI subjects (Figure 1). The stair ascent task elicited increased medial hamstring EMG activity, stair descent produced decreased gluteus medius EMG activity, and early sit-to-stand produced decreased rectus femoris EMG activity in FAI subjects, as compared to healthy controls.Conclusion:Overall the kinematic, kinetic and EMG repeatability was very reliable; these measures are sufficiently reliable to objectively assess dynamic function in healthy and pathologic subjects. Kinematic and kinetic data have shown striking differences between the kinematic and kinetic data of control and FAI subjects, particularly the increased external rotation moments and pelvic flexion during sit to stand for subjects with FAI. We hypothesize that increased pelvic flexion with FAI may be a reason why patients develop impingement and symptoms. Likewise, the decreased medial hamstring and rectus femoris activation in FAI subjects may be an attempt to decrease lumbar lordosis, which may be a compensatory behavior to decrease anterior impingement. In addition, we hypothesize that decreased gluteus medius EMG activity in FAI patients is a sign of abductor fatigue. This study provides a foundation to assess specific gait abnormalities associated with FAI, which will advance the understanding of this pathology and direct future treatment regimens.

Non-invasive measurement of the patellofemoral movements during knee extension–flexion: A validation study

BackgroundThis study compared the difference between patellofemoral kinematics derived simultaneously from patellar bone pin and skin sensors during full range of tibiofemoral joint movement. MethodsMovements at the tibiofemoral and patellofemoral joints during passive full extension–flexion of the knees in three un-embalmed human cadavers were studied with four electromagnetic tracking sensors at a sampling rate of 30Hz. A total of four sensors were attached on distal femur, proximal tibia, the surface of a tailor-made patella mold and at the tip of a plastic bone pin planted in the patellar body through a window on the mold. Paired-sample Wilcoxon signed rank test was used to compare peak motions computed from different sensors. The correlation of the movement–time curves derived from different sensors was tested by coefficient of multiple correlations (CMC) in different sections of tibiofemoral joint range. ResultsPeak motions detected by skin sensor for patellar lateral tilt (p=0.045), distal translation (p=0.021), lateral shift (p=0.032), and anterior–posterior shift of patella (p=0.03 and 0.01 respectively) were higher than that by the bone pin sensor. The overall CMC values for anterior–posterior translation and medial–lateral shift were lower than movements in other planes of movement. The CMC values in initial range were higher than that in the middle and end range in all planes of movement. ConclusionsPatellofemoral kinematics derived from skin sensors may not be representative of the underlying patellar motion. Kinematics reported from the skin sensors should be carefully interpreted.

Direct comparison of measured and calculated total knee replacement force envelopes during walking in the presence of normal and abnormal gait patterns

Knee joint forces measured from instrumented implants provide important information for testing the validity of computational models that predict knee joint forces. The purpose of this study was to validate a parametric numerical model for predicting knee joint contact forces against measurements from four subjects with instrumented TKRs during the stance phase of gait. Model sensitivity to abnormal gait patterns was also investigated. The results demonstrated good agreement for three subjects with relatively normal gait patterns, where the difference between the mean measured and calculated forces ranged from 0.05 to 0.45 body weights, and the envelopes of measured and calculated forces (from three walking trials) overlapped. The fourth subject, who had a “quadriceps avoidance” external moment pattern, initially had little overlap between the measured and calculated force envelopes. When additional constraints were added, tailored to the subject’s gait pattern, the model predictions improved to complete force envelope overlap. Coefficient of multiple determination analysis indicated that the shape of the measured and calculated force waveforms were similar for all subjects (adjusted coefficient of multiple correlation values between 0.88 and 0.92). The parametric model was accurate in predicting both the magnitude and waveform of the contact force, and the accuracy of model predictions was affected by deviations from normal gait patterns. Equally important, the envelope of forces generated by the range of solutions substantially overlapped with the corresponding measured envelope from multiple gait trials for a given subject, suggesting that the variable strategic processes of in vivo force generation are covered by the solution range of this parametric model.

Automatic tracking of medial gastrocnemius fascicle length during human locomotion

During human locomotion lower extremity muscle-tendon units undergo cyclic length changes that were previously assumed to be representative of muscle fascicle length changes. Measurements in cats and humans have since revealed that muscle fascicle length changes can be uncoupled from those of the muscle-tendon unit. Ultrasonography is frequently used to estimate fascicle length changes during human locomotion. Fascicle length analysis requires time consuming manual methods that are prone to human error and experimenter bias. To bypass these limitations, we have developed an automatic fascicle tracking method based on the Lucas-Kanade optical flow algorithm with an affine optic flow extension. The aims of this study were to compare gastrocnemius fascicle length changes during locomotion using the automated and manual approaches and to determine the repeatability of the automated approach. Ultrasound was used to examine gastrocnemius fascicle lengths in eight participants walking at 4, 5, 6, and 7 km/h and jogging at 7 km/h on a treadmill. Ground reaction forces and three dimensional kinematics were recorded simultaneously. The level of agreement between methods and the repeatability of the automated method were quantified using the coefficient of multiple correlation (CMC). Regardless of speed, the level of agreement between methods was high, with overall CMC values of 0.90 ± 0.09 (95% CI: 0.86-0.95). Repeatability of the algorithm was also high, with an overall CMC of 0.88 ± 0.08 (95% CI: 0.79-0.96). The automated fascicle tracking method presented here is a robust, reliable, and time-efficient alternative to the manual analysis of muscle fascicle length during gait.

Precision and repeatability analysis of Optotrak Certus as a tool for gait analysis utilizing a 3D robot

In both scientific and clinical investigations, the precision and repeatability of instruments are demanded; however, precision of motion analysis systems has been reported in the literature rarely and studies are generally not comparable. This study introduces a new method of determining precision and repeatability of Optotrak Certus, a motion analysis tool for gait analysis using a three dimensional (3D) robot. Using 3D robot as reference of standard for distance, the angle and velocity measurement, the accuracy and precision of the Optotrak Certus in terms of angle, distance between markers were quantitated. The standard deviation (SD) and the coefficient of variation (CV) provide a measure of precision whereas the coefficient of multiple correlation (CMC) provides a measure of repeatability. Experimental results containing CMC, CV and SD values for variation of angle, volume, circular movement and speed were demonstrated to analyze the repeatability; hence the repeatability was satisfactory. Angle and distance between markers showed good agreement between measurements, and comparable measures of precision are reported as well as CMC and CV values. The investigation is ethical and practical in measurement analysis in terms of precision and repeatability. Key words: Gait, CMC, CV, precision, repeatability, SD, 3D robot.

A reliability study of biomechanical foot function in psoriatic arthritis based on a novel multi-segmented foot model

The objective of this study was to determine the within-and between-day reliability of spatio-temporal, plantar pressure, kinematic and kinetic measurements based on a novel, seven segment foot model applied in patients with Psoriatic Arthritis (PsA). Nine PsA patients and matched healthy adult controls underwent three-dimensional gait analysis on two occasions, one week apart using a seven segment foot model. A core-set of functional variables including inter-segment kinematics, kinetics, spatio-temporal and plantar pressure distribution were analysed using the coefficient of multiple correlation (CMC), Bland–Altman plots, intraclass correlation coefficients (ICC) and the standard error of measurement (SEM). Results showed excellent within- and between-day reliability for intersegment kinematic and kinetic data patterns with CMC values typically greater than 0.950 in a clinically stable cohort of PsA patients. Between-day reliability ranged from poor to excellent for absolute CMC values. Corrected CMC values were consistently higher across all variables ranging from fair-to-good to excellent. ICC values indicated excellent reliability for discrete spatio-temporal, plantar pressure, and ankle moment and power variables for both groups. Reliability for ground reaction forces and kinematic discrete variables ranged from fair-to-good to excellent. Standard error of measurement values ranged from 0.7° to 3.0° for discrete kinematic variables across both groups with greater variability in the PsA patients. In conclusion, intersegment kinematics and kinetics as well as spatio-temporal and plantar pressure can be reliably measured in PsA patients using a novel seven segment foot model. Some discrete kinematic variables have poor reliability and should not be used in prospective cohort and intervention studies.

The Repeatability of Scapular Rotations Across Three Planes of Humeral Elevation

Measurement of scapular kinematics is an important component in the assessment of shoulder function; however, repeatability of these measurements has not been established. The purpose of this study, therefore, was to determine the repeatability of scapular rotation measures for different humeral elevation planes between trials, sessions, and days. Three-dimensional scapular rotations were collected using an electromagnetic tracking system in three planes of humeral elevation. Coefficient of multiple correlation (CMC) values were calculated between trials, sessions, and days for curves of scapular rotations. CMC values were compared with repeated measures analysis of variance (ANOVAs) and Tukey's post-hoc procedures. Tests of simple main effects were performed for significant interaction effects. Our results suggest that scapular rotation measures are repeatable between trials within the same testing session, but less repeatable between testing sessions and days. Sagittal plane elevation consistently yielded the highest CMC values for all scapular rotations. These results suggest sagittal plane elevation should be considered to evaluate differences in scapular rotations.