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Turning is impaired in people with Parkinson's Disease (PD) and it is a common trigger for freezing of gait (FoG). Recent evidence suggests that people with PD who freeze (PD+FoG) have worse turning performance than those who don't have freezing (non-freezers, PD-FoG), and the freezing episodes are exacerbated by increasing the turn angular amplitude.We investigated the difference between turning 180° while walking versus turning 360° in place, in both single- and dual-task conditions, by means of objective measures in people with PD with and without FoG.Twenty-four PD+FoG and eighteen PD-FoG performed 180° turns while walking and 360° turns in place during single- and dual-task conditions. Quantitative measures of turning and the dual-task cost were computed. Differences were investigated between groups and within turning types using ANOVA. Associations between turn measures and clinical scales were examined with Spearman correlations.Turn duration and the number of steps were greater, and peak angular velocity slower, in PD+FoG compared to PD-FoG (p 0.001). Dual-task costs were similar across groups, but turn duration showed significant interaction (p = 0.03). Posture Instability and Gait Disability (PIGD) subscore was associated with all turn measures in PD-FoG; whereas PIGD was mainly associated with turning while walking in PD+FoG.Objective measures of turning revealed differences between people with and without FoG, specifically, people with FoG showed more impairments in 360° turning in place compared to 180° turning while walking. However, as the turning challenges were increased by adding a dual-task, results from PD+FoG were similar to those from PD-FoG.

Contains fulltext : 220639pub.pdf (Publisher’s version ) (Open Access) Contains fulltext : 220639pos.pdf (Author’s version postprint ) (Open Access) Background. People with Parkinson's disease and freezing of gait (FOG+) have more falls, postural instability and cognitive impairment compared with FOG-. Objective. To conduct a secondary analysis of the V-TIME study, a randomized, controlled investigation showing a greater reduction of falls after virtual reality treadmill training (TT + VR) compared with usual treadmill walking (TT) in a mixed population of fallers. We addressed whether these treadmill interventions led to similar gains in FOG+ as in FOG-. Methods. A total of 77 FOG+ and 44 FOG- were assigned randomly to TT + VR or TT. Participants were assessed pre- and posttraining and at 6 months' follow-up. Main outcome was postural stability assessed by the Mini Balance Evaluation System Test (Mini-BEST) test. Falls were documented using diaries. Other outcomes included the New Freezing of Gait Questionnaire (NFOG-Q) and the Trail Making Test (TMT-B). Results. Mini-BEST scores and the TMT-B improved in both groups after training (P = .001), irrespective of study arm and FOG subgroup. However, gains were not retained at 6 months. Both FOG+ and FOG- had a greater reduction of falls after TT + VR compared with TT (P = .008). NFOG-Q scores did not change after both training modes in the FOG+ group. Conclusions. Treadmill walking (with or without VR) improved postural instability in both FOG+ and FOG-, while controlling for disease severity differences. As found previously, TT + VR reduced falls more than TT alone, even among those with FOG. Interestingly, FOG itself was not helped by training, suggesting that although postural instability, falls and FOG are related, they may be controlled by different mechanisms.

Early-Onset Ataxia (EOA) and Developmental Coordination Disorder (DCD) are two conditions that affect coordination in children. Phenotypic identification of impaired coordination plays an important role in their diagnosis. Gait is one of the tests included in rating scales that can be used to assess motor coordination.A practical problem is that the resemblance between EOA and DCD symptoms can hamper their diagnosis. In this study we employed inertial sensors and a supervised classifier to obtain an automatic classification of the condition of participants. Data from shank and waist mounted inertial measurement units were used to extract features during gait in children diagnosed with EOA or DCD and age-matched controls. We defined a set of features from the recorded signals and we obtained the optimal features for classification using a backward sequential approach. We correctly classified 80.0%, 85.7%, and 70.0% of the control, DCD and EOA children, respectively. Overall, the automatic classifier correctly classified 78.4% of the participants, which is slightly better than the phenotypic assessment of gait by two pediatric neurologists (73.0%). These results demonstrate that automatic classification employing signals from inertial sensors obtained during gait maybe used as a support tool in the differential diagnosis of EOA and DCD. Furthermore, future extension of the classifier's test domains may help to further improve the diagnostic accuracy of pediatric coordination impairment. In this sense, this study may provide a first step towards incorporating a clinically objective and viable biomarker for identification of EOA and DCD. (C) 2016 Elsevier B.V. All rights reserved.

Accurate step detection is crucial for the estimation of gait spatio-temporal parameters. Although several step detection methods based on the use of inertial measurement units (IMUs) have been successfully proposed, they may not perform adequately when the foot is dragged while walking, when walking aids are used, or when walking at low speed. The aim of this study was to test an original step-detection method, the inter-foot distance step counter (IFOD), based on the direct measurement of the distance between feet. Gait data were recorded using a wearable prototype system (SWING2DS), which integrates an IMU and two time-of-flight distance sensors (DSs). The system was attached to the medial side of the right foot with one DS positioned close to the forefoot (FOREDS) and the other close to the rearfoot (REARDS). Sixteen healthy adults were asked to walk over ground for two minutes along a loop, including both rectilinear and curvilinear portions, during two experimental sessions. The accuracy of the IFOD step counter was assessed using a stereo-photogrammetric system as gold standard. The best performance was obtained for REARDS with an accuracy higher than 99.8% for the instrumented foot step and 88.8% for the non-instrumented foot step during both rectilinear and curvilinear walks. Key features of the IFOD step counter are that it is possible to detect both right and left steps by instrumenting one foot only and that it does not rely on foot impact dynamics. The IFOD step counter can be combined with existing IMU-based methods for increasing step-detection accuracy.

In this single blind randomized controlled trial, we examined the effect of a virtual reality-based training on gait of people with multiple sclerosis.Twenty-five individuals with multiple sclerosis with mild to moderate disability were randomly assigned to either the control group (n = 11) or the experimental group (n = 14). The subjects in the control group received treadmill training. Subjects in the experimental group received virtual reality based treadmill training. Clinical measures and gait parameters were evaluated.Subjects in both the groups significantly improved the walking endurance and speed, cadence and stride length, lower limb joint ranges of motion and powers, during single and dual task gait. Moreover, subjects in the experimental group also improved balance, as indicated by the results of the clinical motor tests (p 0.05). Between-group comparisons revealed that the experimental group improved significantly more than control group in hip range of motion and hip generated power at terminal stance at post-training.Our results support the perceived benefits of training programs that incorporate virtual reality to improve gait measures in individuals with multiple sclerosis. Implication of rehabilitation Gait deficits are common in multiple sclerosis (85%) and worsen during dual task activities. Intensive and progressive treadmill training, with and without virtual reality, is effective on dual task gait in persons with multiple sclerosis. Virtual reality-based treadmill training requiring obstacle negotiation increases the range of motion and the power generated at the hip, consequently allowing longer stride length and, consequently, higher gait speed.

Gait analysis is recognized as a useful assessment tool in the field of human movement research. However, doubts remain on its real effectiveness as a clinical tool, i.e. on its capability to change the diagnostic-therapeutic practice. In particular, the conditions in which evidence of a favorable cost-benefit ratio is found and the methodology for properly conducting and interpreting the exam are not identified clearly. To provide guidelines for the use of Gait Analysis in the context of rehabilitation medicine, SIAMOC (the Italian Society of Clinical Movement Analysis) promoted a National Consensus Conference which was held in Bologna on September 14th, 2013. The resulting recommendations were the result of a three-stage process entailing i) the preparation of working documents on specific open issues, ii) the holding of the consensus meeting, and iii) the drafting of consensus statements by an external Jury. The statements were formulated based on scientific evidence or experts’ opinion, when the quality/quantity of the relevant literature was deemed insufficient. The aim of this work is to disseminate the consensus statements. These are divided into 13 questions grouped in three areas of interest: 1) General requirements and management, 2) Methodological and instrumental issues, and 3) Scientific evidence and clinical appropriateness. SIAMOC hopes that this document will contribute to improve clinical practice and help promoting further research in the field.

Bio-imaging techniques represent a powerful tool for shoulder joint biomechanical analysis. However, the restricted field of view may prevent the acquisition of complete scapula and humerus bone models and hence limiting the applicability of standardized anatomical coordinate system (ACS) definitions. The aim of this study was to propose ACS definitions for both scapula and humerus which can be implemented when limited portions of the relevant bones are available. Magnetic resonance (MR) images of twenty right humeri and scapulae were acquired. The proposed ACSs were assessed in terms of (1) sensitivity to bone morphological variation, (2) intra – and inter – operator repeatability and (3) consistency with the anatomical cardinal directions. A comparison with alternative ACS definitions was also performed. Overall, our ACS scapular proposal and that presented in Kedgley and Dunning (2010) were found to be the least sensitive to the morphometric variability (mean angular absolute deviation lower than 8.3 deg) and they were characterized by a high intra – and inter – operator repeatability (mean angular absolute deviation lower than 1.5 deg). The humeral ACS proposal showed a morphometric variability similar to Amadi et al. (2009b) (mean angular absolute deviation lower than 8.3 deg) but a higher reproducibility. The scapular and humeral ACS mean angular deviation from the reference anatomical cardinal directions were smaller than 15 deg and 8.6 deg, respectively. The proposed scapular and humeral ACS definitions are therefore suitable to be applied when a limited portion of the glenohumeral joint is available as it may occur in standard shoulder clinical exams.

The effects of current athletic footwear on lower extremity biomechanics are unknown. The aim of this study was to examine the changes, if any, that occur in peak lower extremity net joint moments while walking in industry recommended athletic footwear. Sixty-eight healthy young adults underwent kinetic evaluation of lower extremity extrinsic joint moments while walking barefoot and while walking in current standard athletic footwear matched to the foot mechanics of each subject while controlling for speed. A secondary analysis was performed comparing peak knee joint extrinsic moments during barefoot walking to those while walking in three different standard footwear types: stability, motion control, and cushion. 3-D motion capture data were collected in synchrony with ground reaction force data collected from an instrumented treadmill. The shod condition was associated with a 9.7% increase in the first peak knee varus moment, and increases in the hip flexion and extension moments. These increases may be largely related to a 6.5% increase in stride length with shoes associated with increases in the ground reaction forces in all three axes. The changes from barefoot walking observed in the peak knee joint moments were similar when subjects walked in all three footwear types. It is unclear to what extent these increased joint moments may be clinically relevant, or potentially adverse. Nonetheless, these differences should be considered in the recommendation as well as the design of footwear in the future.

Objective To determine the effect of modern-day running shoes on lower extremity joint torques during running. Design Two-condition experimental comparison. Setting A 3-dimensional motion analysis laboratory. Participants A total of 68 healthy young adult runners (37 women) who typically run in running shoes. Methods All subjects ran barefoot and in the same type of stability running footwear at a controlled running speed. Three-dimensional motion capture data were collected in synchrony with ground reaction force data from an instrumented treadmill for each of the 2 conditions. Main Outcome Measurements Peak 3-dimensional external joint torques at the hip, knee, and ankle as calculated through a full inverse dynamic model. Results Increased joint torques at the hip, knee, and ankle were observed with running shoes compared with running barefoot. Disproportionately large increases were observed in the hip internal rotation torque and in the knee flexion and knee varus torques. An average 54% increase in the hip internal rotation torque, a 36% increase in knee flexion torque, and a 38% increase in knee varus torque were measured when running in running shoes compared with barefoot. Conclusions The findings at the knee suggest relatively greater pressures at anatomical sites that are typically more prone to knee osteoarthritis, the medial and patellofemoral compartments. It is important to note the limitations of these findings and of current 3-dimensional gait analysis in general, that only resultant joint torques were assessed. It is unknown to what extent actual joint contact forces could be affected by compliance that a shoe might provide, a potentially valuable design characteristic that may offset the observed increases in joint torques.

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.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.The kinematics of treadmill and overground gait were very similar. Twelve of 22 kinematic parameter maxima were statistically significantly different (p0.05), 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 (p0.05) 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.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.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.

Partial body weight support (PBWS) systems used for rehabilitation status post-neurological and musculoskeletal pathologies and injuries are traditionally passive. Our purpose was to demonstrate the ability of an actively controlled PBWS system to provide a clinically relevant modulated support condition while investigating the impact of such a condition on the dynamics of gait. Using an instrumented treadmill and a motion capture system, we compared gait parameters of six healthy young adults (age 24–31 years) during unsupported walking to those under the assistance of two support conditions (a constant 20% body weight support, and a modulated support providing 20% body weight support during the loading response of each leg while allowing for an unsupported terminal stance). The modulated condition achieved support synchronized to gait cycle events with mean and maximum loading errors at the 20% body weight support level equal to 1.01 and 2.44 kg, respectively. Constant support significantly reduced sagittal plane hip angle range of motion and increased ankle platarflexion as compared to unsupported walking (p

Gait and cognitive deficits are common in multiple sclerosis (MS) and are negatively affected during dual-task walking. Treadmill (TM) training has been previously used to preserve locomotor activity in MS. Virtual reality (VR) engages the user in cognitive and motor activities simultaneously. A training combining TM and VR has been successfully adopted in several neurological diseases, but not in MS. This study aims at investigating the feasibility of a VR-based TM training program on gait of subjects with MS. Eight persons with relapsing-remitting MS were recruited to participate in a six-week VR-based TM training program. Gait analysis was performed both in single and dual task conditions. Clinical tests were used to assess walking endurance and obstacle negotiation. All the evaluations were performed before, immediately and one month after the training. Gait speed and stride length improved in dual task post-intervention and were retained at follow-up. An improved ability in negotiating obstacles was found across the evaluations. VR-based TM training program is feasible and safe for MS subjects with moderate disabilities and may positively affect gait under complex conditions, such as dual tasking and obstacle negotiation.

Background Burn contractures are common and difficult to treat. Measuring continuous joint motion would inform the assessment of contracture interventions; however, it is not standard clinical practice. This study examines use of an interactive gaming system to measure continuous joint motion data. Objective To assess the usability of an exoskeleton-based interactive gaming system in the rehabilitation of upper extremity burn contractures. Design Feasibility study. Setting Eight subjects with a history of burn injury and upper extremity contractures were recruited from the outpatient clinic of a regional inpatient rehabilitation facility. Methods Subjects used an exoskeleton-based interactive gaming system to play 4 different video games. Continuous joint motion data were collected at the shoulder and elbow during game play. Main Outcome Measures Visual analog scale for engagement, difficulty and comfort. Angular range of motion by subject, joint, and game. Results The study population had an age of 43 ± 16 (mean ± standard deviation) years and total body surface area burned range of 10%-90%. Subjects reported satisfactory levels of enjoyment, comfort, and difficulty. Continuous joint motion data demonstrated variable characteristics by subject, plane of motion, and game. Conclusions This study demonstrates the feasibility of use of an exoskeleton-based interactive gaming system in the burn population. Future studies are needed that examine the efficacy of tailoring interactive video games to the specific joint impairments of burn survivors.

When using optoelectronic stereophotogrammetry, skin deformation and displacement causes marker movement with respect to the underlying bone. This movement represents an artifact, which affects the estimation of the skeletal system kinematics, and is regarded as the most critical source of error in human movement analysis. A comprehensive review of the state-of-the-art for assessment, minimization and compensation of the soft tissue artifact (STA) is provided. It has been shown that STA is greater than the instrumental error associated with stereophotogrammetry, has a frequency content similar to the actual bone movement, is task dependent and not reproducible among subjects and, of lower limb segments, is greatest at the thigh. It has been shown that in in vivo experiments only motion about the flexion/extension axis of the hip, knees and ankles can be determined reliably. Motion about other axes at those joints should be regarded with much more caution as this artifact produces spurious effects with magnitudes comparable to the amount of motion actually occurring in those joints. Techniques designed to minimize the contribution of and compensate for the effects of this artifact can be divided up into those which model the skin surface and those which include joint motion constraints. Despite the numerous solutions proposed, the objective of reliable estimation of 3D skeletal system kinematics using skin markers has not yet been satisfactorily achieved and greatly limits the contribution of human movement analysis to clinical practice and biomechanical research. For STA to be compensated for effectively, it is here suggested that either its subject-specific pattern is assessed by ad hoc exercises or it is characterized from a large series of measurements on different subject populations. Alternatively, inclusion of joint constraints into a more general STA minimization approach may provide an acceptable solution.

Background The step-by-step determination of the spatio-temporal parameters of gait is clinically relevant since it provides an estimation of the variability of specific gait patterns associated with frequent geriatric syndromes. In recent years, several methods, based on the use of magneto-inertial units (MIMUs), have been developed for the step-by-step estimation of the gait temporal parameters. However, most of them were applied to the gait of healthy subjects and/or of a single pathologic population. Moreover, spatial parameters in pathologic populations have been rarely estimated step-by-step using MIMUs. The validity of clinically suitable MIMU-based methods for the estimation of spatio-temporal parameters is therefore still an open issue. The aim of this study was to propose and validate a method for the determination of both temporal and spatial parameters that could be applied to normal and heavily compromised gait patterns. Methods Two MIMUs were attached above each subject’s ankles. An instrumented gait mat was used as gold standard. Gait data were acquired from ten hemiparetic subjects, ten choreic subjects, ten subjects with Parkinson’s disease and ten healthy older adults walking at two different gait speeds. The method detects gait events (GEs) taking advantage of the cyclic nature of gait and exploiting some lower limb invariant kinematic characteristics. A combination of a MIMU axes realignment along the direction of progression and of an optimally filtered direct and reverse integration is used to determine the stride length. Results Over the 4,514 gait cycles analyzed, neither missed nor extra GEs were generated. The errors in identifying both initial and final contact at comfortable speed ranged between 0 and 11 ms for the different groups analyzed. The stride length was estimated for all subjects with less than 3% error. Conclusions The proposed method is apparently extremely robust since gait speed did not substantially affect its performance and both missed and extra GEs were avoided. The spatio-temporal parameters estimates showed smaller errors than those reported in previous studies and a similar level of precision and accuracy for both healthy and pathologic gait patterns. The combination of robustness, precision and accuracy suggests that the proposed method is suitable for routine clinical use. Electronic supplementary material The online version of this article (doi:10.1186/1743-0003-11-152) contains supplementary material, which is available to authorized users.

The evaluation of the glenohumeral joint laxity requires the estimate of displacements of the humeral head centre (HHC) with respect to the glenoid. To the authors׳ knowledge, several studies have been conducted to estimate HHC translations in vivo but data under anterior loading conditions has not been collected yet. Aim of this study was to develop a non-invasive experimental methodology based on magnetic resonance (MR) imaging for the in vivo evaluation of the HHC translations due to an anteriorly directed force. Fourteen asymptomatic shoulders were acquired using a horizontal open MR scanner with the subjects in the supine position both at 15° and 90° of arm abduction with and without an anterior force of 20 N applied at the HHC level. When no load was applied, from 15° to 90° of arm abduction, the HHC moved, anteriorly (1.5±1.3 mm) and superiorly (1.8±1.3 mm) while smaller displacements were observed medio-laterally (0.4±0.7 mm). Under the application of the anterior force the 3D displacement of the HHC with respect to the glenoid was 1.6±1.2 mm and 1.3 ±0.7 mm, respectively at 15° and 90° of arm abduction. The level of precision associated to the GHJ translation was less than 0.33 mm along all directions i.e. one order of magnitude smaller than the relevant translations. In conclusion, the MRI-based methodology allowed for the analysis of HHC displacements under conditions of anterior loads within an acceptable level of reliability.

We evaluated the effect of reducing the vertical displacement of the centre of mass (COM) on the six determinants of gait proposed by Saunders, Inman and Eberhart in 30 healthy adults. We compared the estimated reduction in COM vertical displacement due to the determinants in their compass model with the actual reduction of vertical displacement. The maximum height of the COM for the compass gait model occurred earlier than the actual COM maximum height. Different gait functions were determinant in reducing COM vertical displacement. In both cases heel rise was the main determinant (up to 2/3 of total reduction). Pelvic obliquity and single stance knee flexion contributions were more important when compass gait COM maximum was used while they were barely detectable at the actual COM maximum. Ipsi- and contra-lateral knee flexion were detrimental to the reduction of COM vertical displacements, while pelvic rotation contribution was beneficial and accounted for up to 10% of the overall COM vertical displacement reduction. Although a reduction of COM vertical displacement may have important energy implications, determining the specific gait parameters associated with this function is fundamental in understanding gait disability.

Kerrigan DC, Della Croce U, Marciello M, Riley PO. A refined view of the determinants of gait: significance of heel rise. Arch Phys Med Rehabil 2000;81:1077-80. Objectives: Although the major determinants of gait described by Saunders and colleagues have been accepted for more than 40 years, recent investigations raise the question of whether the reduction in center of mass (COM) displacement compared with a compass gait model indeed results from the factors originally described. We tested the hypothesis that heel rise at the end of stance is a true determinant that can explain a considerable portion of the reduction in COM vertical displacement during walking. Design: Stereophotogrammetric data during walking were collected. A modified compass gait model incorporating the effect of heel rise, as compared with predictions based on a standard compass model, were used to estimate the isolated effect of heel rise on reducing the vertical displacement of COM. Setting: A gait laboratory. Participants: Thirty able-bodied subjects. Main Outcome Measure: The estimated reduction in COM displacement due to heel rise was compared with the actual reduction in displacement. Results: The estimated effect of heel rise on reduction in COM displacement was 23.4 ± 7.6mm, whereas the actual reduction in COM displacement was 21.2 ± 6.5mm (difference not significant, paired p = .185). Conclusion: During normal walking, heel rise from foot flat has a considerable role in raising the height of the COM when it is at its lowest, thus reducing its overall displacement. Insofar as reduction of COM vertical displacement may have important energy implications, appreciating the specific gait parameter of heel rise is key in rehabilitative approaches to improve gait disability. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Objective: To analyze the role of the rectus femoris muscle in nondisabled gait at various walking velocities using fine-wire dynamic electromyography. Design: Descriptive study. Fine-wire electromyography data were collected from the rectus femoris during level walking at four walking speeds. Rectus femoris activity patterns in the loading response phase and the pre- and initial-swing phase of the gait cycle were compared using paired t tests. Setting: A gait laboratory. Subjects: Ten nondisabled adult volunteers. Main Outcome Measures: Amplitude of rectus femoris activity in the loading response phase and the pre- and initial-swing phase during walking at four speeds. Results: There was a bimodal pattern of rectus femoris activity in all subjects, at all speeds, in both phases, with high variability in the onsets, durations, and amplitudes of activity, and paired t tests revealed no significant differences ( p > .05) between phases at any walking speed. Conclusion: Activity in the rectus femoris in the pre- and initial-swing phase in nondisabled individuals at all speeds suggests that similar activity detected in individuals with stiff-legged gait may not be inappropriate.

s / Gait & Posture 42S (2015) S1–S27 S5 Fig. 1. (a) Reference image. Model generated after the manual identification of the relevant anatomical landmarks. (b) Tracked model in a dynamic frame. They wore an underwear garment with a coloured patch applied, and uniformly coloured ankle socks used as segmentalmarkers (for pelvis and feet, respectively). A RGB video camera (Vicon Bonita 720C, 60 fps) was placed laterally to the walkway. Synchronous 3D marker positions were captured with a Vicon system (Bonita10). Markers were positioned according to the Davis protocol [3] (GS). The proposed ML methodology requires a preliminary model calibration step, performed on a reference image of the subject standing upright (Fig. 1a), from which a foot contour model template is automatically identified, while the lateral malleolus, lateral epicondyle and greater trochanter are manually identified [2]. Model templates of the shank and thigh segments are defined bymeans of technical reference points identified on the silhouette contour. The pelvis orientation is assumed to coincidewith the orientation of the segment obtained by interpolating the points extracted from the pelvis patch. For eachgait trial, the silhouette contourof themoving subject was extracted using a background subtraction technique, and the foot and pelvis segmental markers were identified using colour filters. The foot orientation was determined by matching the foot template with the foot current image. The shank and thigh reference points on the deformed silhouette contour were identified for each frame, and the corresponding templates fitted using a SVD procedure (Fig. 1b) [2]. The kinematic estimations provided by theMLmethodwere compared to the GS in terms of correlation coefficient (CC) and root mean square deviation (RMSD). Results: The CC (and RMSD) between the ML and the GS estimations ranged from 0.91 (4.9◦) to 0.98 (7.3◦) for the hip flexextension, from0.94 (5.4◦) to 0.97 (8.3◦) for the knee flex-extension and from0.74 (5.9◦) to0.84 (9.9◦) for theankledorsi-plantarflexion. Discussion: Joint kinematics estimatedusingML showed a good correlation with the GS joint kinematics (0.74≤CC≤0.98), however the relevant errors are clearly larger than those found in healthy adults [2] (up to 9.9◦). This difference can be attributed partly to the children’s body segments small size (particularly for the foot) and in some cases to the presence of the arm swing that reduces the visibility of the pelvis segmental marker. Therefore, the extraction of the segmental markers will have to be improved in order for this method to be applied in clinical settings.

Objectives: It is not known whether changes in the biomechanics of elderly gait are related to aging per se, or to reduced walking speed in this population. The goals of the present study were to identify specific biomechanical changes, independent of speed, that might impair gait performance in healthy older people by identifying age-associated changes in the biomechanics of gait, and to determine which of these changes persist at increased walking speed. Design: Stereophotogrammetric and force platform data were collected. Differences in peak joint motion (kinematic) and joint moment and power (kinetic) values between healthy young and elderly subjects at comfortable and increased walking speed were measured. Setting: A gait laboratory. Subjects: Thirty-one healthy elderly (age 65 to 84 years) and 31 healthy young adult subjects (age 18 to 36 years), all without known neurologic, musculoskeletal, cardiac, or pulmonary problems. Main Outcome Measures: All major peak kinematic and kinetic variables during the gait cycle. Results: Several kinematic and kinetic differences between young and elderly adults were found that did not persist when walking speed was increased. Differences that persisted at both comfortable and fast walking speeds were reduced peak hip extension, increased anterior pelvic tilt, and reduced ankle plantarflexion and ankle power generation. Conclusion: Gait performance in the elderly may be limited by both subtle hip flexion contracture and ankle plantarflexor concentric weakness. Results of the current study should motivate future experimental trials of specific hip flexor stretching and ankle plantarflexor concentric strengthening exercises to preserve and potentially improve walking performance in the elderly.

A previous study demonstrated that when one knee is artificially immobilized, a contralateral shoe-lift improves the oxygen cost of walking. This study was undertaken to evaluate the kinematic and kinetic effects associated with this shoe-lift.Motion analysis and force platform data were collected in subjects walking (1) normally, (2) with one knee immobilized, (3) with one knee immobilized and with a one-half-inch shoe-lift applied to the contralateral, nonimmobilized shoe, and (4) with a one-inch shoe-lift similarly applied. Kinematic and kinetic data from three trials of each condition were compared graphically and statistically using a repeated measures analysis of variance.A gait laboratory.Eight able-bodied subjects without known neurologic or musculoskeletal problems.Fifty-two peak kinematic and kinetic variables during various phases of the gait cycle.Statistically significant differences (p.05) between the normal and immobilized knee conditions were noted in 22 variables; however, significant differences between the immobilized knee conditions were found in only 4 variables. There were small improvements with the shoe-lifts toward normal in peak hip abduction, hip abduction at 20% to 30% of the gait cycle, and in peak knee extension moment on the nonimmobilized side. There was a small change away from normal in peak knee extension moment on the immobilized-side for the 1" shoe-lift.Wearing a contralateral shoe-lift when one knee is immobilized is associated with only small changes in kinematic and kinetic parameters. The shoe-lift may slightly reduce the need for compensatory hip abduction and vaulting on the nonimmobilized side. Importantly, no adverse biomechanic effect from the shoe-lift was noted except for a slightly increased peak knee extension moment on the immobilized side found for the 1" but not the 1"/2 shoe-lift.

Three methods of estimating the vertical displacement of the center of mass (COM) during level walking were compared in 30 consecutive patients with gait disability. The methods were: (1) sacral marker method, (2) segmental analysis method and (3) force plate method. The force plate method produced data with a lower range and a different distribution than the other two methods. There was no significant difference between the data of the sacral marker and segmental analysis methods (Johnson's modified t-test, P = 0.16). These two methods are likely more accurate and sensitive methods of estimating the changes in the vertical displacement of COM than the force plate method. The segmental analysis method is prone to errors because the model and anthropometric estimations used may not be applicable to every patient. The sacral marker method is a simple, inexpensive, effective and accurate tool to estimate the vertical displacement of the COM.

Objectives To determine whether a knee brace incorporating inflatable air bladders can alter the net peak external knee adduction moment in persons with medial compartment knee osteoarthritis. Design Prospective cohort study. Setting Motion analysis laboratory. Participants Subjects (n = 18) diagnosed with knee osteoarthritis as defined by the Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association. Methods Instrumented gait analysis was performed while subjects walked with and without the knee brace. When subjects wore the knee brace, the air bladders were either uninflated or inflated to 7 psi. The net external knee adduction moment was obtained by subtracting the abduction moment produced by the knee brace (estimated using a finite element analysis model) from the external knee adduction moment (estimated using a camera-based motion analysis system). Main Outcome Measurements The net external knee adduction moment was compared across all testing conditions. Results A 7.6% decrease in net peak external knee adduction moment was observed when subjects wore the knee brace uninflated compared with when they did not wear the brace. Inflation of the bladders to 7 psi led to a 26.0% decrease in net peak external knee adduction moment. Conclusions The results of the study suggest that the effects of an unloading knee brace may be enhanced by incorporating inflatable air bladders into the design of the brace, thus leading to an improved correction of the excessive peak external knee adduction moment observed in patients with medial compartment knee osteoarthritis.

Background The estimation of the spatio-temporal gait parameters is of primary importance in both physical activity monitoring and clinical contexts. A method for estimating step length bilaterally, during level walking, using a single inertial measurement unit (IMU) attached to the pelvis is proposed. In contrast to previous studies, based either on a simplified representation of the human gait mechanics or on a general linear regressive model, the proposed method estimates the step length directly from the integration of the acceleration along the direction of progression. Methods The IMU was placed at pelvis level fixed to the subject's belt on the right side. The method was validated using measurements from a stereo-photogrammetric system as a gold standard on nine subjects walking ten laps along a closed loop track of about 25 m, varying their speed. For each loop, only the IMU data recorded in a 4 m long portion of the track included in the calibrated volume of the SP system, were used for the analysis. The method takes advantage of the cyclic nature of gait and it requires an accurate determination of the foot contact instances. A combination of a Kalman filter and of an optimally filtered direct and reverse integration applied to the IMU signals formed a single novel method (Kalman and Optimally filtered Step length Estimation - KOSE method). A correction of the IMU displacement due to the pelvic rotation occurring in gait was implemented to estimate the step length and the traversed distance. Results The step length was estimated for all subjects with less than 3% error. Traversed distance was assessed with less than 2% error. Conclusions The proposed method provided estimates of step length and traversed distance more accurate than any other method applied to measurements obtained from a single IMU that can be found in the literature. In healthy subjects, it is reasonable to expect that, errors in traversed distance estimation during daily monitoring activity would be of the same order of magnitude of those presented.

A markerless technique is proposed and applied to estimate the two-dimensional joint kinematics of the shank and foot complex during the stance phase. Image sequences were acquired with a single camera from three healthy subjects while walking barefoot and with socks. Automatic segmentation of the shank and foot was performed to isolate the moving body from the background. A multi-rigid body model for the shank and foot complex, with the relevant segment anatomical axes, was defined and an image cross-correlation technique was applied to detect the anatomical axes locations throughout the movement. The proposed markerless technique was validated by acquiring the same trials also with a stereophotogrammetric marker-based system and a simple marker set. Differences in the joint kinematics estimates obtained with the two techniques fall in most cases within the intra-subject variability showing that, in selected applications, the markerless technique may replace more expensive and more experimental time demanding marker-based techniques.

s / Gait & Posture 42S (2015) S1–S27 S3 Table 1 Morphological and structural features in CP and TD children. Age [years] Muscle volume [cm3] Muscle length [cm] MTU [cm] Average muscle area [cm2] Normalized Muscle volume [cm2] Mean EI of muscle CP 8.6±2.3 32.4±13.8 16.2±3.9 33.5±6.0 2.1±0.5 1.1±0.3 101.0±9.7 TD 9.2±2.3 52.2±19.0 17.3±2.7 34.0±4.9 2.9±0.7 1.5±0.4 129.2±20.3 t-Test (p-value) 0.740 0.103 0.331 0.566 0.018* 0.040* 0.006* volume (=volume/MTU length) were calculated. In addition, the mean EI value (expressed in a grey-scale of 256 values), was also evaluated. Comparisons were made using the Student t-test (unpaired). Statistical significance (*) was set to p 0.79, p>0.01), but with a lower slope in CP (5.2 vs. 7.8 cm3/years). In CP, a significant negative correlation was found between EI and average muscle area (R2 =0.60, p=0.04). Discussion: We found a smaller muscle volume in CP children, as previously reported [2]. Interestingly, as a CP child ages, slower muscle growth occurs than in the TD children. Averaged muscle area was found to be more sensitive to distinguish between TD and CP children. Furthermore, the MG was hyper-echoic in the CP group relative to the TD group, supporting our hypothesis. Combining EI and average muscle area shows potential in estimating the amount of fibrotic changes occurring within a muscle. Utilising the new approach for 3D reconstruction offers an objective and efficient manner to diagnose muscle and tendon morphological and structural changes in the clinical environment.

s / Gait & Posture 42S (2015) S1–S27 S25 Table 1 FClmax true values and estimate errors in the two tasks performed by E and PD subjects. Group Overground walking Obstacle passing Val true± sd [mm] (sd) [mm] mae [mm] mae% Val true± sd [mm] (sd) [mm] mae [mm] mae% E 124 ± 26 −1 (12) 9 7% 297 ± 25 1 (10) 8 3% PD 119 ± 16 3 (9) 8 6% 304 ± 63 3 (20) 14 5% the solid phase and interstitial fluid pressure. It is shown that they evolve as long as the number of steps increases. Contact pressures with the ground are also obtained, which can be directly compared with plantar pressures measured during experimental tests. Discussion: Two highly outstanding achievements are reached by this approach. First, the real time-dependent behavior of the plantar tissue is captured thus allowing for considering the influence of the number and the duration of gait cycles and their alterations. Second, the distribution of stress peaks is available in the whole domain of interest, and the poroelastic behavior shows the location of total stresses and effective ones. This distinction can be very useful in the study of ulceration triggering and the porous media approach adds very useful information to the those already available by the gait analysis acquisitions.

were 8.2±3.2◦, 10.2±3.7◦ and 8.8±5.3◦ in group A, and 7.3±3.5◦, 12.6±2.6◦ and 12.5±4.2◦ in group B. EMG analysis revealed prolonged activation of the medial/lateral vasti muscles in group A. Such muscle co-contraction was not generally observed in all patients in group B, this being proving more stability in the knee joint after TKA according KA. Discussion: These results reveal that better function occurs usingKA thanNMA inTKR. Though small differenceswereobserved between TKR groups in terms of motion data, the higher data consistency and the less prolonged muscle activations identified using KA support the claim of a more natural soft tissue balance in corresponding knees. More patients are needed to establish the superiority of KA.

Agnese Peruzzi1,2,∗, Andrea Cereatti 1,2, Roberto Zarbo3, Anat Mirelman4, Ugo Della Croce1,2 1 Information Engineering Unit, PolComIng Department, University of Sassari, Sassari, Italy 2 Interuniversity Centre of Bioengineering of the Human Neuromusculoskeletal System, Sassari, Italy 3 Department of Clinical and Experimental Medicine, University of Sassari, Sassari, Italy 4 Department of Neurology, Tel Aviv Sourasky Medical Center, Tel Aviv University, Tel Aviv, Israel

Functional recovery of an impaired gait pattern is a common goal for stroke patients in their rehabilitation. Robotic and mechatronic devices offer a means of facilitating and enhancing gait retraining practices undertaken by clinicians. A new active knee orthosis has been developed for gait retraining of stroke patients that may fulfill this role. Since this device is newly developed, it is important to determine its impact on the walking patterns of healthy individuals before exploring its use in gait retraining of stroke patients. The aim of this study was to analyze adaptations in gait mechanics of healthy subjects due to the added mass of the knee orthosis while worn uni-laterally and bi-laterally. In our preliminary tests we observed significant deviations from normal gait patterns when the knee orthosis was worn uni-laterally. Conversely, minor gait deviations were seen when the knee orthosis was worn bi-laterally. This suggests that a bilateral configuration may be more suited for gait retraining purposes.

Background The assessment of the accuracy of the pose estimation of human bones and consequent joint kinematics is of primary relevance in human movement analysis. This study evaluated the performance of selected pose estimators in reducing the effects of instrumental errors, soft tissue artifacts and anatomical landmark mislocations occurring at the thigh on the determination of the knee kinematics. Methods The pattern of a typical knee flexion-extension during a gait cycle was fed into a knee model which generated a six-components knee kinematics and relevant marker trajectories. The marker trajectories were corrupted with both instrumental noise and soft tissue artifacts. Two different cluster configurations (4 and 12-marker cluster) were investigated. Four selected pose estimators, a Geometrical method, a SVD-based method, and the Pointer Cluster Technique in the optimized and non optimized version, were analyzed. The estimated knee kinematics were compared to the nominal kinematics in order to evaluate the accuracy of the selected pose estimators. Results Results have shown that optimal pose estimators perform better than traditional geometric pose estimators when soft tissue artifacts are present. The use of redundant markers improved in some cases the estimation of the dynamics of the kinematics patterns, while it does not reduce the offsets from the nominal kinematics curves. Overall, the best performance was obtained by the SVD-based pose estimator, while the performance of the PCT pose estimator in its optimal version was not satisfactory. However, the knee kinematics errors reached 5 deg for rotations and 10 mm for translations). Conclusion Given the favorable experimental conditions of this study (soft tissue artifacts determined from a young, healthy and non overweight subject), the errors found in estimating the knee kinematics have to be considered unsatisfactory even if the best performing pose estimator is used. Therefore, it is the authors' opinion that the movement analysis research community should make additional efforts in the search of more subject specific error models to increase the accuracy of joint kinematics estimations.

Kinetics during stair ambulation is currently studied via either the use of sensing elements embedded in the steps of the stairway or simple rigid blocks of different height positioned on top of existing force platforms, typically embedded in a walkway for gait analysis. Neither of these approaches is truly satisfactory for gait analysis laboratories. The first one is expensive and requires setting up a dedicated space. The second approach is limited by the number of platforms utilized in the laboratory for evaluating level walking. This communication proposes a novel design, referred to as "interlaced stairway", that allows one to measure ground reaction force and position of the center of pressure (CoP) for four foot contacts during stair ambulation using only two force platforms embedded in a walkway. Accuracy and precision of the CoP estimates and natural frequency of the stairway structure were derived from experimental data. Test results indicate that the interlaced stairway structure does not appreciably reduce the quality of the measures gathered by the existing force platforms. Specifically, the estimated CoP coordinates show good agreement with the horizontal coordinates of the geometric center of the calibration object utilized to assess accuracy and precision of the CoP estimates (max difference < 6 mm). The natural frequency of the stairway structure is lower than the one for the unloaded force platform but higher than the frequency components of interest in stair ambulation analysis.

Kerrigan DC, Johansson JL, Bryant MG, Boxer JA, Della Croce U, Riley PO. Moderate-heeled shoes and knee joint torques relevant to the development and progression of knee osteoarthritis. Objective To determine if women's dress shoes with heels of just 1.5in (3.8cm) in height increases knee joint torques, which are thought to be relevant to the development and/or progression of knee osteoarthritis (OA) in both the medial and patellofemoral compartments. Design Randomized controlled trial. Setting A 3-dimensional motion analysis gait laboratory. Participants Twenty-nine healthy young women (age, 26.7±5.0y) and 20 healthy elderly adult women (age, 75.3±6.5y). Interventions Not applicable. Main outcome measures Peak external varus knee torque in early and late stance and prolongation of flexor knee torque in early stance. Three-dimensional data on lower-extremity torques and motion were collected during walking while (1) wearing shoes with 1.5-in high heels and (2) wearing control shoes without any additional heel. Data were plotted and qualitatively compared; major peak values and timing were statistically compared between the 2 conditions using paired t tests. Results Peak knee varus torque during late stance was statistically significantly greater with the heeled shoes than with the controls, with increases of 14% in the young women and 9% in the elderly women. With the heeled shoes, the early stance phase knee flexor torque was significantly prolonged, by 19% in the young women and by 14% in elderly women. Also, the peak flexor torque was 7% higher with the heeled shoe in the elderly women. Conclusions Even shoes with moderately high heels (1.5in) significantly increase knee torques thought to be relevant in the development and/or progression of knee OA. Women, particularly those who already have knee OA, should be advised against wearing these types of shoes.

The identification of quantitative tools to assess an individual's mobility limitation is a complex and challenging task. Several motor tasks have been designated as potential indicators of mobility limitation. In this study, a multiple motor task obtained by sequencing sit-to-stand and upright posture was used. Algorithms based on data obtained exclusively from a single force platform were developed to detect the timing of the motor task phases (sit-to-stand, preparation to the upright posture and upright posture). To test these algorithms, an experimental protocol inducing predictable changes in the acquired signals was designed. Twenty-two young, able-bodied subjects performed the task in four different conditions: self-selected natural and high speed with feet kept together, and self-selected natural and high speed with feet pelvis-width apart. The proposed algorithms effectively detected the timing of the task phases, the duration of which was sensitive to the four different experimental conditions. As expected, the duration of the sit-to-stand was sensitive to the speed of the task and not to the foot position, while the duration of the preparation to the upright posture was sensitive to foot position but not to speed. In addition to providing a simple and effective description of the execution of the motor task, the correct timing of the studied multiple task could facilitate the accurate determination of variables descriptive of the single isolated phases, allowing for a more thorough description of the motor task and therefore could contribute to the development of effective quantitative functional evaluation tests.

We investigated the relationship of hip, knee and ankle function to gait speed in healthy elderly subjects. We hypothesized that the hip extension moment would make a significantly smaller contribution to propulsion power in the elderly than in healthy young subjects even when the elders were ambulating at speeds comparable to those of the young subjects. We analyzed the free speed gait of 16 young and 14 elderly subjects, and the fast gait of the elder subjects. In elderly subjects free speed gait linear power transfer from the leg to the upper body due to the hip and knee moments was decreased compared with young subjects walking at their normal gait speed. However, when asked to walk fast, elders significantly increase knee and hip moment contributions to hip linear power to levels comparable to those of young subjects at a similar speed. These results refute our hypothesis and support our earlier findings indicating that kinematic alterations at the hip are a cause of reduced gait speed in the elderly.

Kerrigan DC, Riley PO, Lelas JL, Della Croce U. Quantification of pelvic rotation as a determinant of gait. Arch Phys Med Rehabil 2001;82:217-20. Objective: To evaluate the effect of pelvic rotation, originally described as the first determinant of gait, on reducing the vertical displacement of the center of mass (COM) during comfortable speed walking. Design: Pelvic and lower extremity kinematic data during walking were collected. A modified compass gait model incorporating measured inputs was used to estimate the effect of pelvic rotation on reducing the vertical displacement of the COM. The actual reduction in vertical displacement was also calculated. Setting: A gait laboratory. Participants: Thirty able-bodied subjects. Main Outcome Measure: The estimated reduction in COM vertical displacement caused by pelvic rotation was compared with the actual reduction in COM displacement. Results: The estimated effect of pelvic rotation in reducing COM displacement was 2.5 ± 1.1mm, accounting for only 12% of the actual reduction. Conclusion: During normal comfortable speed walking by able-bodied subjects, pelvic rotation contributes only a small portion of the actual reduction in the vertical displacement of the COM compared with a compass gait model. Other primary gait factors or determinants are needed to explain the actual reduction in vertical displacement of the COM.

Understanding propulsion and adaptation to speed requirements is important in determining appropriate therapies for gait disorders. We hypothesize that adaptations for changing speed requirements occur primarily at the hip. The slow, normal and fast gait of 24 healthy young subjects was analyzed. The linear power was analyzed at the hip joint. The anterior}posterior and vertical induced accelerations of the hip were also determined. Linear power and anterior}posterior-induced acceleration (IA) analyses of the hip reveal that the lower limb joint’s moments contribute to body forward propulsion primarily during late swing and early stance. Propulsive adaptations to speed changes occur primarily at the hip and secondarily at the ankle. These analyses show that hip muscles, particularly the hip extensors, are critical to propulsion. They also show that ankle function is primarily for support, but is important to propulsion, especially at slow speeds. ( 2001 Elsevier Science Ltd. All rights reserved.

Kerrigan DC, Riley PO, Nieto TJ, Della Croce U. Knee joint torques: comparison between women and men during barefoot walking. Arch Phys Med Rehabil 2000;81:1162-5. Objective: To determine if knee joint torques, which are likely relevant to the development and, possibly, progression of knee osteoarthritis, are equivalent between genders during natural, barefoot walking. Design: Collected stereophotogrammetric and force platform data during comfortable, barefoot walking. Knee joint torques were plotted and statistically compared between genders using both an unpaired t test ( p Setting: A gait laboratory. Participants: One hundred ten healthy, nondisabled young women and men. Main Outcome Measures: Four knee joint torque parameters normalized for height and weight: (1) peak and (2) duration of sagittal flexor joint torque from early to midstance, and (3) first and (4) second peak coronal (frontal) varus torque values during the stance period. Results: No statistically significant differences between genders were found, and the values were equivalent between genders for each of the 4 knee joint torque parameters. Conclusion: These findings support the hypothesis that under similar barefoot conditions women and men have a similar intrinsic biomechanic risk for knee osteoarthritis. Future research to assess the effects of other potential biomechanic factors, such as shoe-wear and activity type, may assist not only in preventing knee joint osteoarthritis, but also in developing new rehabilitative strategies to treat osteoarthritis of the knee. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

In three dimensional (3-D) human movement analysis using close-range photogrammetry, surface marker clusters deform and rigidly move relative to the underlying bone. This introduces an important artefact (skin movement artefact) which propagates to bone position and orientation and joint kinematics estimates. This occurs to the extent that those joint attitude components that undergo small variations result in totally unreliable values. This paper presents an experimental and analytical procedure, to be included in a subject-specific movement analysis protocol, which allows for the assessment of skin movement artefacts and, based on this knowledge, for their compensation. The effectiveness of this procedure was verified with reference to knee-joint kinematics and to the artefacts caused by the hip movements on markers located on the thigh surface. Quantitative validation was achieved through experimental paradigms whereby prior reliable information on the target joint kinematics was available. When position and orientation of bones were determined during the execution of a motor task, using a least-squares optimal estimator, but the rigid artefactual marker cluster movement was not dealt with, then knee joint translations and rotations were affected by root mean square errors (r.m.s.) up to 14 mm and 6 degrees, respectively. When the rigid artefactual movement was also compensated for, then r.m.s errors were reduced to less than 4 mm and 3 degrees, respectively. In addition, errors originally strongly correlated with hip rotations, after compensation, lost this correlation.

The interpretation of data obtained in a movement analysis laboratory is a crucial issue in clinical contexts. Collection of such data in large databases might encourage the use of modern techniques of data mining to discover additional knowledge with automated methods. In order to maximise the size of the database, simple and low-cost experimental set-ups are preferable. The aim of this study was to extract knowledge inherent in the sit-to-stand task as performed by healthy adults, by searching relationships among measured and estimated biomechanical quantities. An automated method was applied to a large amount of data stored in a database. The sit-to-stand motor task was already shown to be adequate for determining the level of individual motor ability. The technique of search for association rules was chosen to discover patterns as part of a Knowledge Discovery in Databases (KDD) process applied to a sit-to-stand motor task observed with a simple experimental set-up and analysed by means of a minimum measured input model. Selected parameters and variables of a database containing data from 110 healthy adults, of both genders and of a large range of age, performing the task were considered in the analysis. A set of rules and definitions were found characterising the patterns shared by the investigated subjects. Time events of the task turned out to be highly interdependent at least in their average values, showing a high level of repeatability of the timing of the performance of the task. The distinctive patterns of the sit-to-stand task found in this study, associated to those that could be found in similar studies focusing on subjects with pathologies, could be used as a reference for the functional evaluation of specific subjects performing the sit-to-stand motor task.

An improved characterization of the dynamics of postural sway can provide a better understanding about the functional organization of the postural control system as well as a more robust tool for postural pattern recognition. To this aim, a novel parameterization was applied to the stabilogram diffusion analysis formerly proposed by Collins and De Luca [Collins JJ, De Luca CJ. Open-loop and closed-loop control of posture: a random-walk analysis of center-of-pressure trajectories. Exp Brain Res 1993;95:308-18] that considered the act of maintaining posture as a stochastic process. The main purpose of the present technique was to overcome some drawbacks of the model presented by Collins and De Luca that may restrain its potential application in clinical practice. The approach uses a unique non-linear model to describe the center of pressure (COP) dynamics that reduces the number of parameters and decreases their intra-subject variability; consequently, fewer trials are required to perform reliable estimates of stochastic parameters and this is of particular importance for subjects that cannot afford many repeated measurements because of age or pathology. Four new statistical mechanics parameters (NSMP) were computed on the log-log stabilogram diffusion plots and their estimates were compared in terms of reliability and sensitivity to the visual conditions with: (1) a minimal set of four summary statistic scores (SSS); and (2) the six statistical mechanics parameters (SMP) proposed by Collins and De Luca. All four NSMP showed at least a fair-to-good reliability (intraclass correlation coefficient, ICC=0.49) while SMP (ICC=0.20) showed some poor reliability. A better overall reliability was also observed with respect to SSS. Moreover, only NSMP had a similar score for eyes open and eyes closed conditions. Three out of four NSMP were also significantly sensitive to eyes open or closed conditions (P