Collective excitability in highly diluted random networks of oscillators.

We report on collective excitable events in a highly diluted random network of non-excitable nodes. Excitability arises thanks to a self-sustained local adaptation mechanism that drives the system on a slow timescale across a hysteretic phase transition involving states with different degrees of synchronization. These phenomena have been investigated for the Kuramoto model with bimodal distribution of the natural frequencies and for the Kuramoto model with inertia and a unimodal frequency distribution. We consider global and partial stimulation protocols and characterize the system response for different levels of dilution. We compare the results with those obtained in the fully coupled case showing that such collective phenomena are remarkably robust against network diluteness.

Rehabilitation and Return to Sport Assessment after Anterior Cruciate Ligament Injury: Quantifying Joint Kinematics during Complex High-Speed Tasks through Wearable Sensors.

The aim of the present study was to quantify joint kinematics through a wearable sensor system in multidirectional high-speed complex movements used in a protocol for rehabilitation and return to sport assessment after Anterior Cruciate Ligament (ACL) injury, and to validate it against a gold standard optoelectronic marker-based system. Thirty-four healthy athletes were evaluated through a full-body wearable sensor (MTw Awinda, Xsens) and a marker-based optoelectronic (Vicon Nexus, Vicon) system during the execution of three tasks: drop jump, forward sprint, and 90° change of direction. Clinically relevant joint angles of lower limbs and trunk were compared through Pearson's correlation coefficient (r), and the Coefficient of Multiple Correlation (CMC). An excellent agreement (r > 0.94, CMC > 0.96) was found for knee and hip sagittal plane kinematics in all the movements. A fair-to-excellent agreement was found for frontal (r 0.55-0.96, CMC 0.63-0.96) and transverse (r 0.45-0.84, CMC 0.59-0.90) plane kinematics. Movement complexity slightly affected the agreement between the systems. The system based on wearable sensors showed fair-to-excellent concurrent validity in the evaluation of the specific joint parameters commonly used in rehabilitation and return to sport assessment after ACL injury for complex movements. The ACL professionals could benefit from full-body wearable technology in the on-field rehabilitation of athletes.

A Canine Gait Analysis Protocol for Back Movement Assessment in German Shepherd Dogs.

Objective-To design and test a motion analysis protocol for the gait analysis of adult German Shepherd (GS) dogs with a focus in the analyses of their back movements. Animals-Eight clinically healthy adult large-sized GS dogs (age, 4 ± 1.3 years; weight, 38.8 ± 4.2 kg). Procedures-A six-camera stereo-photogrammetric system and two force platforms were used for data acquisition. Experimental acquisition sessions consisted of static and gait trials. During gait trials, each dog walked along a 6 m long walkway at self-selected speed and a total of six gait cycles were recorded. Results-Grand mean and standard deviation of ground reaction forces of fore and hind limbs are reported. Spatial-temporal parameters averaged over gait cycles and subjects, their mean, standard deviation and coefficient of variance are analyzed. Joint kinematics for the hip, stifle and tarsal joints and their average range of motion (ROM) values, and their 95% Confidence Interval (CI) values of kinematics curves are reported. Conclusions and Clinical Relevance-This study provides normative data of healthy GS dogs to form a preliminary basis in the analysis of the spatial-temporal parameters, kinematics and kinetics during quadrupedal stance posture and gait. Also, a new back movement protocol enabling a multi-segment back model is provided. Results show that the proposed gait analysis protocol may become a useful and objective tool for the evaluation of canine treatment with special focus on the back movement.

Knee joint sagittal plane movement in cerebral palsy: a comparative study of 2-dimensional markerless video and 3-dimensional gait analysis.

Background and purpose - Gait analysis is indicated in children with cerebral palsy (CP) to identify and quantify gait deviations. One particularly difficult-to-treat deviation, crouch gait, can progress in adolescence and ultimately limit the ability to ambulate. An objective quantitative assessment is essential to early identify progressive gait impairments in children with CP. 3-dimensional gait analysis (3D GA) is considered the gold standard, although it is expensive, seldom available, and unnecessarily detailed for screening and follow-up. Simple video assessments are time-consuming when processed manually, but more convenient if used in conjunction with video processing algorithms; this has yet been validated in CP. We validate a 2-dimensional markerless (2D ML) assessment of knee joint flexion/extension angles of the gait cycle in children and young adults with CP. Patients and methods - 18 individuals, mean age 15 years (6.5-28), participated. 11 had bilateral, 3 unilateral, 3 dyskinetic, and 1 ataxic CP. In the Gross Motor Function Classification System, 6 were at level I, 11 at level II, and 1 at level III. We compared 2D ML, using a single video camera with computer processing, and 3D GA. Results - The 2D ML method overestimated the knee flexion/extension angle values by 3.3 to 7.0 degrees compared with 3D GA. The reliability within 2D ML and 3D GA was mostly good to excellent. Interpretation - Despite overestimating, 2D ML is a reliable and convenient tool to assess knee angles and, more importantly, to detect changes over time within a follow-up program in ambulatory children with CP.

A 2D Markerless Gait Analysis Methodology: Validation on Healthy Subjects.

A 2D markerless technique is proposed to perform lower limb sagittal plane kinematic analysis using a single video camera. A subject-specific, multisegmental model of the lower limb was calibrated with the subject in an upright standing position. Ankle socks and underwear garments were used to track the feet and pelvis segments, whereas shank and thigh segments were tracked by means of reference points identified on the model. The method was validated against a marker based clinical gait model. The accuracy of the spatiotemporal parameters estimation was found suitable for clinical use (errors between 1% and 3% of the corresponding true values). Comparison analysis of the kinematics patterns obtained with the two systems revealed high correlation for all the joints (0.82 < R(2) < 0.99). Differences between the joint kinematics estimates ranged from 3.9 deg to 6.1 deg for the hip, from 2.7 deg to 4.4 deg for the knee, and from 3.0 deg to 4.7 deg for the ankle. The proposed technique allows a quantitative assessment of the lower limb motion in the sagittal plane, simplifying the experimental setup and reducing the cost with respect to traditional marker based gait analysis protocols.

Validation of a method for real time foot position and orientation tracking with Microsoft Kinect technology for use in virtual reality and treadmill based gait training programs.

The use of virtual reality for the provision of motor-cognitive gait training has been shown to be effective for a variety of patient populations. The interaction between the user and the virtual environment is achieved by tracking the motion of the body parts and replicating it in the virtual environment in real time. In this paper, we present the validation of a novel method for tracking foot position and orientation in real time, based on the Microsoft Kinect technology, to be used for gait training combined with virtual reality. The validation of the motion tracking method was performed by comparing the tracking performance of the new system against a stereo-photogrammetric system used as gold standard. Foot position errors were in the order of a few millimeters (average RMSD from 4.9 to 12.1 mm in the medio-lateral and vertical directions, from 19.4 to 26.5 mm in the anterior-posterior direction); the foot orientation errors were also small (average %RMSD from 5.6% to 8.8% in the medio-lateral and vertical directions, from 15.5% to 18.6% in the anterior-posterior direction). The results suggest that the proposed method can be effectively used to track feet motion in virtual reality and treadmill-based gait training programs.

Identifying gait events without a force plate during running: a comparison of methods.

This paper presents a comparison of four different methods of identifying the times of foot-strike and toe-off during running based on gait marker trajectories. The event times predicted by the methods were compared to those identified using a force plate for both over-ground and treadmill running. The effect of using different threshold values for the detection of gait events using force plate data was also investigated, and as a result, all assessments of event detection accuracy were based on a cut-off value of 10N. The most accurate method of foot-strike detection depended on whether the runner landed with a rear- or a mid-foot strike. For rear-foot-strike running, the best method of identifying foot-strike used the vertical acceleration profile of the posterior heel distal marker and the vertical position profile of the hallux marker. For mid-foot-strike running, the best method of identifying foot-strike used the vertical velocity profile of the mean positions of the posterior heel distal marker and a marker midway between the second and third metatarsal heads. The most accurate method of identifying toe-off did not depend on type of foot-strike and was based on the vertical acceleration and position profiles of the hallux marker.

Altered ankle kinematics and shank-rear-foot coupling in those with chronic ankle instability.

CONTEXT: Kinematic patterns during gait have not been extensively studied in relation to chronic ankle instability (CAI). OBJECTIVE: To determine whether individuals with CAI demonstrate altered ankle kinematics and shank-rear-foot coupling compared with controls during walking and jogging. DESIGN: Case control. SETTING: Motion-analysis laboratory. PARTICIPANTS: 7 participants (3 men, 4 women) suffering from CAI (age 24.6 +/- 4.2 y, height 172.6 +/- 9.4 cm, mass 70.9 +/- 8.1 kg) and 7 (3 men, 4 women) healthy, matched controls (age 24.7 +/- 4.5 y, height 168.2 +/- 5.9 cm, mass 66.5 +/- 9.8 kg). INTERVENTIONS: Subjects walked and jogged on a treadmill while 3-dimensional kinematics of the lower extremities were captured. MAIN OUTCOME MEASURES: The positions of rear-foot inversion-eversion and shank rotation were calculated throughout the gait cycle. Continuous relative-phase angles between these segments were calculated to assess coupling. RESULTS: The CAI group demonstrated more rear-foot inversion and shank external rotation during walking and jogging. There were differences between groups in shank-rear-foot coupling during terminal swing at both speeds. CONCLUSIONS: Altered ankle kinematics and joint coupling during the terminal-swing phase of gait may predispose a population with CAI to ankle-inversion injuries. Less coordinated movement during gait may be an indication of altered neuromuscular recruitment of the musculature surrounding the ankle as the foot is being positioned for initial contact.

Effects of balance training on gait parameters in patients with chronic ankle instability: a randomized controlled trial.

OBJECTIVE: To examine the effects of a four-week balance training programme on ankle kinematics during walking and jogging in those with chronic ankle instability. A secondary objective was to evaluate the effect of balance training on the mechanical properties of the lateral ligaments in those with chronic ankle instability. DESIGN: Randomized controlled trial. SETTING: Laboratory. SUBJECTS/PATIENTS: Twenty-nine participants (12 males, 17 females) with self-reported chronic ankle instability were randomly assigned to a balance training group or a control group. INTERVENTION: Four weeks of supervised rehabilitation that emphasized dynamic balance stabilization in single-limb stance. The control group received no intervention. MAIN OUTCOME MEASURES: Kinematic measures of rearfoot inversion/eversion, shank rotation, and the coupling relationship between these two segments throughout the gait cycle during walking and jogging on a treadmill. Instrumented ankle arthrometer measures were taken to assess anterior drawer and inversion talar tilt laxity and stiffness. RESULTS: No significant alterations in the inversion/eversion or shank rotation kinematics were found during walking and jogging after balance training. There was, however, a significant decrease in the shank/rearfoot coupling variability during walking as measured by deviation phase after balance training (balance training posttest: 13.1 degrees +/- 6.2 degrees , balance training pretest: 16.2 degrees +/- 3.3 degrees , P = 0.03), indicating improved shank/rearfoot coupling stability. The control group did not significantly change. (posttest: 16.30 degrees +/- 4.4 degrees , pretest: 18.6 degrees +/- 7.1 degrees , P40.05) There were no significant changes in laxity measures for either group. CONCLUSIONS: Balance training significantly altered the relationship between shank rotation and rearfoot inversion/eversion in those with chronic ankle instability.

A new anatomically based protocol for gait analysis in children.

Human movement analysis still suffers from the weakness of the currently used protocols for data collection and reduction. Reliable data comparisons and precise functional assessment require anatomically based definitions of the reference axes and frames, and therefore careful identification and tracking of the landmarks. When impaired children are analysed, the marker-set and other measurement procedures have to be minimised to reduce the time of the experiment and ensure patient collaboration. A new protocol is proposed for the analysis of pelvis and lower limb motion obtained as a compromise between these two requirements. A marker-set is proposed which involves the attachment of 22 skin markers, the calibration by a pointer of 6 anatomical landmarks, and the identification of the hip joint centre by a prediction approach. Anatomical reference frames and joint rotations are defined according to current recommendations. The protocol was assessed by analysing a single child in several repetitions by different examiners, and a population of 10 healthy children, mean age 9.7-years-old. The entire analysis was repeated after subtraction of the offset by static posture angles. The minimum and maximum means of the standard deviations from five examiners of the same child were respectively 2.1 degrees in pelvic obliquity and 6.8 degrees in knee rotation. The minimum and maximum means of the standard deviations from the 10 healthy children were 2.1 degrees in pelvic obliquity and 9.6 degrees in knee internal-external rotation. The protocol is feasible and allows 3D anatomical-based measurements of segment and joint motion and data sharing according to current standards.

A kinematic and kinetic comparison of overground and treadmill walking in healthy subjects.

INTRODUCTION: Gait evaluation protocols using instrumented treadmills will be increasingly used in the near future. For this reason, it must be shown that using instrumented treadmills will produce measures of the ground reaction force adequate for inverse dynamic analysis, and differences between treadmill and overground gait must be well characterized. METHODS: Overground walking kinetics were estimated with the subjects walking at their self-selected comfortable walking speed. For the treadmill gait trials, the subjects walked on two treadmills, such that heel-strike occurred on the forward treadmill and toe-off occurred on the trailing treadmill. The treadmill was set to the average overground walking speed. Overground and treadmill data were evaluated using Vicon Plug-in Gait. The differences between the maxima and minima of kinematic and kinetic parameters for overground and treadmill gait were evaluated. RESULTS: The kinematics of treadmill and overground gait were very similar. Twelve of 22 kinematic parameter maxima were statistically significantly different (p<0.05), but the magnitude of the difference was generally less than 2 degrees . All GRF maxima were found to be statistically significantly smaller for treadmill versus overground gait (p<0.05) as were 15 of 18 moment, and 3 of 6 power maxima. However, the magnitude of the differences was comparable to the variability in normal gait parameters. The sagittal plane ankle moments were not statistically different for treadmill and overground gait. DISCUSSION: We have shown that treadmill gait is qualitatively and quantitatively similar to overground gait. Differences in kinematic and kinetic parameters can be detected in matched comparisons, particularly in the case of kinetic parameters. However, the magnitudes of these differences are all within the range of repeatability of measured kinematic parameters. Thus, the mechanics of treadmill and overground gait are very similar. CLINICAL SIGNIFICANCE: Having demonstrated the essential equivalence of treadmill and overground gait, it is now possible for clinical movement analysis to take advantage of treadmill-based protocols.

Testing of a tri-instrumented-treadmill unit for kinetic analysis of locomotion tasks in static and dynamic loading conditions.

In this study, we present a multi-treadmill system instrumented with three force platforms capable of measuring vertical and shear ground reaction forces and moments during both walking and running. Linearity, belts speed variations, repeatability of the measures, cross-talk, natural frequency, instrumental noise, moving part induced noise and drift were investigated. The noise due to vibrations and to moving parts was also investigated having a subject walking and running on the treadmill. The linearity test results showed a high linearity of all three treadmill force platforms, and vertical force natural frequency values of 219, 308, 307Hz, obtained for the three force platforms, were considered appropriate for the investigation of walking and running. The instrumental noise did not appear to be a significant source of error. The characteristics of the noise due to vibrations and moving parts changed when in the presence of a subject walking and running on the treadmill. For walking trials, averaging of gait cycles led to a systematic improvement of the signal to noise ratio, particularly for the medio-lateral component of the force. For running trials, even though averaging was not as beneficial as for walking trials, the greater force amplitude led to a better signal to noise ratio value. This instrumented treadmill demonstrated acceptable accuracy and signal to noise ratios for all ground reaction force components such that it can be useful for a variety of research and clinical gait analysis applications.

Soft tissue artefact assessment in humeral axial rotation.

The accuracy of upper-limb kinematic data acquired from optoelectronic systems with retro-reflective markers is poor, mainly due to soft tissue artefact (STA). For the upper-arm, humeral internal/external rotation (HIER) is the movement most affected by STA, which is measured as a percentile fraction (K) of the effective humeral axial rotation performed. The aim of this work was to quantify STA during HIERs, with independently varying attitude of the humerus and elbow flexion, and to test the possibility of estimating its mean value over the tested upper-limb orientations using one simple trial. Six able-bodied subjects performed a series of HIERs in combination with elbow flexion for different humeral planes and degrees of elevation. During the trials the instantaneous attitudes of two humeral anatomical frames were compared, one being affected by the STA to be measured, and the other assumed as the gold standard. K was found to range from 20% to 48% of the effective humeral axial rotation performed, depending on the subject, humeral attitude and elbow flexion. These last two factors comparably affect STA and resulted in mean K coefficients of variation among the subjects of about 9% and 7%, respectively. Common patterns of K with elbow flexion and humerus elevation are discussed. The data also show that the mean of K of a subject is very close to the value assessed in a specific upper-limb configuration consistent among the subjects. This result from this study could be used to build up a time-saving STA compensation procedure suitable for clinical applications.