In the movement analysts community, the assessment of the displacement of skin photogrammetric ma... more In the movement analysts community, the assessment of the displacement of skin photogrammetric markers relative to the underlying bone (soft tissue displacement, STD) is considered to be a priority. The aim of this study is to present a non-invasive method that allows for the characterization of STD for any marker location, subject, and motor task. In particular, this method provides an estimate of the STD vector in a bone-embedded frame. The body segment under analysis is endowed with the largest possible number of skin markers located over all areas of interest. Any given STD vector is observed from all the marker cluster frames that can be built by suitably combining all the available markers. A subset of the latter frames is identified that is made of frames endowed with uncorrelated local movements. The estimate of a given STD vector is determined through the coherent average of the vectors reconstructed using the above-mentioned independent frames. This estimate is affected by a 1801 phase indeterminacy.
Ieee Transactions on Evolutionary Computation, 2014
ABSTRACT Reliable knowledge of in vivo joint kinematics is fundamental in clinical medicine. Fluo... more ABSTRACT Reliable knowledge of in vivo joint kinematics is fundamental in clinical medicine. Fluoroscopic motion tracking theoretically permits a millimeter/degree level of accuracy in 3D joint motion analysis, but the reliability of the local optimization algorithm (Levenberg-Marquardt, LMA), typically used for the pose estimation, is highly operator dependent. A new Memetic Algorithm (MA), hybridizing global evolution and a local search metaphor for learning, is proposed to automate the analysis and improve its reliability and robustness. The performance of MA was assessed for in silico and in vivo elbow kinematics, with and without user supervision. The best learning strategy between Lamarckian and Baldwinian evolution was identified. MA’s accuracy and repeatability was quantified and compared with LMA’s. The algorithm performed best using a partial Lamarckian learning strategy. The geometric symmetry of analysed bony segments influenced the accuracy, whereas the absolute bone pose with respect to the projection geometry affected the repeatability. In contrast to LMA, MA provided robust, repeatable, and operator independent pose estimations, even for in vivo analyses. The pose can be automatically estimated with errors lower than 1 mm and 1 deg for all the pose parameters except the depth position, if the investigated motion task avoids symmetric bony projection silhouettes.
La presente opera può essere liberamente consultata ed utilizzata, può essere riprodotta in via p... more La presente opera può essere liberamente consultata ed utilizzata, può essere riprodotta in via permanente in formato digitale (cd salvataggio) e può esserne effettuata la stampa su carta con apparecchiature private (senza ricorso a terzi operatori professionali), per fini ...
Inertial sensors are becoming widely used for the assessment of human movement in both clinical a... more Inertial sensors are becoming widely used for the assessment of human movement in both clinical and research applications, thanks to their usability out of the laboratory. This work aims to propose a method for calibrating anatomical landmark position in the wearable sensor reference frame with an ease to use, portable and low cost device. An off-the-shelf camera, a stick and a pattern, attached to the inertial sensor, compose the device. The proposed technique is referred to as video Calibrated Anatomical System Technique (vCAST). The absolute orientation of a synthetic femur was tracked both using the vCAST together with an inertial sensor and using stereo-photogrammetry as reference. Anatomical landmark calibration showed mean absolute error of 0.6±0.5 mm: these errors are smaller than those affecting the in-vivo identification of anatomical landmarks. The roll, pitch and yaw anatomical frame orientations showed root mean square errors close to the accuracy limit of the wearable sensor used (1°), highlighting the reliability of the proposed technique. In conclusion, the present paper proposes and preliminarily verifies the performance of a method (vCAST) for calibrating anatomical landmark position in the wearable sensor reference frame: the technique is low time consuming, highly portable, easy to implement and usable outside laboratory.
Journal of Mechanics in Medicine and Biology, 2015
ABSTRACT The gait analysis of subjects with short and non-uniform gait is difficult using the com... more ABSTRACT The gait analysis of subjects with short and non-uniform gait is difficult using the common commercial force platforms. The present work consists in the design, based on finite element method (FEM) analysis, of a force platform of two different dimensions (0.40 × 0.40 m and 0.80 × 0.40 m) considering static and dynamic simulation of their behavior. The aim of this project is to improve, with a simple, low cost and flexible structure, the instrumentation available for the gait analysis of children, neurologic patients and in general the most common clinical cases. The applicability of gait analysis to children, neurologic patients ECC can be improved by the flexibility of force platforms without losing the performance provided by traditional force platforms (e.g., for postural analysis).
Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after... more Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.
Journal of neuroengineering and rehabilitation, 2014
Quantifying gait stability is a topic of high relevance and a number of possible measures have be... more Quantifying gait stability is a topic of high relevance and a number of possible measures have been proposed. The problem in validating these methods is the necessity to identify a-priori unstable individuals. Since proposed methods do not make any assumption on the characteristics of the subjects, the aim of the present study was to test the performance of gait stability measures on individuals whose gait is a-priori assumed unstable: toddlers at the onset of independent walking. Ten toddlers, ten adults and ten elderly subjects were included in the study. Data from toddlers were acquired longitudinally over a 6-month period to test if the methods detected the increase in gait stability with experience, and if they could differentiate between toddlers and young adults. Data from elderly subjects were expected to indicate a stability value in between the other two groups. Accelerations and angular velocities of the trunk and of the leg were measured using two tri-axial inertial sens...
ABSTRACT Twenty infants (age 10-16 month) were analysed using inertial sensors over a 6-month per... more ABSTRACT Twenty infants (age 10-16 month) were analysed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.
Background: Many gait variability and stability measures have been proposed in the literature, wi... more Background: Many gait variability and stability measures have been proposed in the literature, with the aim to quantify gait impairment, degree of neuro-motor control and balance disorders in healthy and pathological subjects. These measures are often obtained from lower trunk acceleration data, typically acquired during rectilinear gait, but relevant experimental protocols and data processing techniques lack in standardization. Since directional changes represent an essential aspect of gait, the assessment of their influence on such measures is essential for standardization. In addition, their investigation is needed to evaluate the applicability of these measures in laboratory trials and in daily life activity analysis. A further methodological aspect to be standardized concerns the assessment of the sampling frequency, which could affect stability measures. The aim of the present study was hence to assess if gait variability and stability measures are affected by directional changes, and to evaluate the influence of sampling frequency of trunk acceleration data on the results. Methods: Fifty-one healthy young adults performed a 6-minute walk test along a 30 m straight pathway, turning by 180 deg at each end of the pathway. Nine variability and stability measures (Standard deviation, Coefficient of variation, Poincaré plots, maximum Floquet multipliers, short-term Lyapunov exponents, Recurrence quantification analysis, Multiscale entropy, Harmonic ratio and Index of harmonicity) were calculated on stride duration and trunk acceleration data (acquired at 100 Hz and 200 Hz) coming from straight walking windows and from windows including both straight walking and the directional change. Results: Harmonic ratio was the only measure that resulted to be affected by directional changes and sampling frequency, decreasing with the presence of a directional change task. HR was affected in the AP and V directions for the 200 Hz, but only in AP direction for the 100 Hz group. Conclusion: Multiscale entropy, short term Lyapunov exponents and Recurrence quantification analysis were generally not affected by directional changes nor by sampling frequency, and could contribute to the definition of a fall risk index in free-walking conditions.
Many measures aiming to assess the stability of human motion have been proposed in the literature... more Many measures aiming to assess the stability of human motion have been proposed in the literature, but still there is no commonly accepted way to define or quantify locomotor stability. Among these measures, orbital stability analysis via Floquet multipliers is still under debate. Some of the controversies concerning the use of this technique could lie in the absence of a standard implementation. The aim of this study was to analyse the influence of i) experimental measurement noise, ii) variables selected for the construction of the state space, and iii) number of analysed cycles on the outputs of orbital stability applied to walking. The analysis was performed on a 2-dimensional 5-link walking model and on a sample of 10 subjects performing long over-ground walks. Noise resulting from stereophotogrammetric and accelerometric measurement systems was simulated in the in-silico analysis. Maximum Floquet multipliers resulted to be affected by both number of analysed strides and state space composition. The effect of experimental noise was found to be slightly more potentially critical when analysing stereophotogrammetric data then when dealing with acceleration data. Experimental and model results were comparable in terms of overall trend, but a difference was found in the influence of the number of analysed cycles.
Journal of Mechanics in Medicine and Biology, 2012
The aim of the present study was to identify the phases of gait and the joints where the \ground ... more The aim of the present study was to identify the phases of gait and the joints where the \ground reaction vector technique" (GRVT) can represent an acceptable alternative to the use of inverse dynamics (ID), when considering subjects with a lower-limb amputation. First, an analytical investigation of the ID of the three joints of the lower limb is given, distinguishing the gravitational, the inertial and the ground reaction contributions. The¯rst two contributions require inertial parameters estimation; for this purpose, literature anthropometric data are typically used, both for the unimpaired and prosthetic limb, as accurate speci¯c inertial parameters for the prosthetic limb are di±cult to obtain from companies or require time consuming estimation. This assumption potentially leads to errors in the three-dimensional (3D) joint moment estimation. Second, the results of two case studies, a trans-femoral amputee with two di®erent prostheses and Journal a trans-tibial amputee, showed that the GRVT can explain the most part of the net joint moment for the ankle and the knee in the whole stance phase, and for the hip in the¯rst part of the stance, leading to a similar clinical evaluation without any assumptions on inertial parameters.
In the movement analysts community, the assessment of the displacement of skin photogrammetric ma... more In the movement analysts community, the assessment of the displacement of skin photogrammetric markers relative to the underlying bone (soft tissue displacement, STD) is considered to be a priority. The aim of this study is to present a non-invasive method that allows for the characterization of STD for any marker location, subject, and motor task. In particular, this method provides an estimate of the STD vector in a bone-embedded frame. The body segment under analysis is endowed with the largest possible number of skin markers located over all areas of interest. Any given STD vector is observed from all the marker cluster frames that can be built by suitably combining all the available markers. A subset of the latter frames is identified that is made of frames endowed with uncorrelated local movements. The estimate of a given STD vector is determined through the coherent average of the vectors reconstructed using the above-mentioned independent frames. This estimate is affected by a 1801 phase indeterminacy.
Ieee Transactions on Evolutionary Computation, 2014
ABSTRACT Reliable knowledge of in vivo joint kinematics is fundamental in clinical medicine. Fluo... more ABSTRACT Reliable knowledge of in vivo joint kinematics is fundamental in clinical medicine. Fluoroscopic motion tracking theoretically permits a millimeter/degree level of accuracy in 3D joint motion analysis, but the reliability of the local optimization algorithm (Levenberg-Marquardt, LMA), typically used for the pose estimation, is highly operator dependent. A new Memetic Algorithm (MA), hybridizing global evolution and a local search metaphor for learning, is proposed to automate the analysis and improve its reliability and robustness. The performance of MA was assessed for in silico and in vivo elbow kinematics, with and without user supervision. The best learning strategy between Lamarckian and Baldwinian evolution was identified. MA’s accuracy and repeatability was quantified and compared with LMA’s. The algorithm performed best using a partial Lamarckian learning strategy. The geometric symmetry of analysed bony segments influenced the accuracy, whereas the absolute bone pose with respect to the projection geometry affected the repeatability. In contrast to LMA, MA provided robust, repeatable, and operator independent pose estimations, even for in vivo analyses. The pose can be automatically estimated with errors lower than 1 mm and 1 deg for all the pose parameters except the depth position, if the investigated motion task avoids symmetric bony projection silhouettes.
La presente opera può essere liberamente consultata ed utilizzata, può essere riprodotta in via p... more La presente opera può essere liberamente consultata ed utilizzata, può essere riprodotta in via permanente in formato digitale (cd salvataggio) e può esserne effettuata la stampa su carta con apparecchiature private (senza ricorso a terzi operatori professionali), per fini ...
Inertial sensors are becoming widely used for the assessment of human movement in both clinical a... more Inertial sensors are becoming widely used for the assessment of human movement in both clinical and research applications, thanks to their usability out of the laboratory. This work aims to propose a method for calibrating anatomical landmark position in the wearable sensor reference frame with an ease to use, portable and low cost device. An off-the-shelf camera, a stick and a pattern, attached to the inertial sensor, compose the device. The proposed technique is referred to as video Calibrated Anatomical System Technique (vCAST). The absolute orientation of a synthetic femur was tracked both using the vCAST together with an inertial sensor and using stereo-photogrammetry as reference. Anatomical landmark calibration showed mean absolute error of 0.6±0.5 mm: these errors are smaller than those affecting the in-vivo identification of anatomical landmarks. The roll, pitch and yaw anatomical frame orientations showed root mean square errors close to the accuracy limit of the wearable sensor used (1°), highlighting the reliability of the proposed technique. In conclusion, the present paper proposes and preliminarily verifies the performance of a method (vCAST) for calibrating anatomical landmark position in the wearable sensor reference frame: the technique is low time consuming, highly portable, easy to implement and usable outside laboratory.
Journal of Mechanics in Medicine and Biology, 2015
ABSTRACT The gait analysis of subjects with short and non-uniform gait is difficult using the com... more ABSTRACT The gait analysis of subjects with short and non-uniform gait is difficult using the common commercial force platforms. The present work consists in the design, based on finite element method (FEM) analysis, of a force platform of two different dimensions (0.40 × 0.40 m and 0.80 × 0.40 m) considering static and dynamic simulation of their behavior. The aim of this project is to improve, with a simple, low cost and flexible structure, the instrumentation available for the gait analysis of children, neurologic patients and in general the most common clinical cases. The applicability of gait analysis to children, neurologic patients ECC can be improved by the flexibility of force platforms without losing the performance provided by traditional force platforms (e.g., for postural analysis).
Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after... more Twenty infants (age 10-16 month) were analyzed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.
Journal of neuroengineering and rehabilitation, 2014
Quantifying gait stability is a topic of high relevance and a number of possible measures have be... more Quantifying gait stability is a topic of high relevance and a number of possible measures have been proposed. The problem in validating these methods is the necessity to identify a-priori unstable individuals. Since proposed methods do not make any assumption on the characteristics of the subjects, the aim of the present study was to test the performance of gait stability measures on individuals whose gait is a-priori assumed unstable: toddlers at the onset of independent walking. Ten toddlers, ten adults and ten elderly subjects were included in the study. Data from toddlers were acquired longitudinally over a 6-month period to test if the methods detected the increase in gait stability with experience, and if they could differentiate between toddlers and young adults. Data from elderly subjects were expected to indicate a stability value in between the other two groups. Accelerations and angular velocities of the trunk and of the leg were measured using two tri-axial inertial sens...
ABSTRACT Twenty infants (age 10-16 month) were analysed using inertial sensors over a 6-month per... more ABSTRACT Twenty infants (age 10-16 month) were analysed using inertial sensors over a 6-month period after the onset of independent walking. Changes in gait temporal parameters, coordination and gait strategies were evaluated. Gait temporal parameters showed a developmental shift at 2 months of walking experience: after this period, a change in the developmental trend was present in most of the analyzed parameters. Cadence results showed that the increased velocity is more due to an increase in step length than to an increase in cadence, after the first two months of independent walking. Different gait strategies were identified during the first month of independent gait based on collected data; after one month, characteristics of the pendulum mechanism were present in each examined toddler.
Background: Many gait variability and stability measures have been proposed in the literature, wi... more Background: Many gait variability and stability measures have been proposed in the literature, with the aim to quantify gait impairment, degree of neuro-motor control and balance disorders in healthy and pathological subjects. These measures are often obtained from lower trunk acceleration data, typically acquired during rectilinear gait, but relevant experimental protocols and data processing techniques lack in standardization. Since directional changes represent an essential aspect of gait, the assessment of their influence on such measures is essential for standardization. In addition, their investigation is needed to evaluate the applicability of these measures in laboratory trials and in daily life activity analysis. A further methodological aspect to be standardized concerns the assessment of the sampling frequency, which could affect stability measures. The aim of the present study was hence to assess if gait variability and stability measures are affected by directional changes, and to evaluate the influence of sampling frequency of trunk acceleration data on the results. Methods: Fifty-one healthy young adults performed a 6-minute walk test along a 30 m straight pathway, turning by 180 deg at each end of the pathway. Nine variability and stability measures (Standard deviation, Coefficient of variation, Poincaré plots, maximum Floquet multipliers, short-term Lyapunov exponents, Recurrence quantification analysis, Multiscale entropy, Harmonic ratio and Index of harmonicity) were calculated on stride duration and trunk acceleration data (acquired at 100 Hz and 200 Hz) coming from straight walking windows and from windows including both straight walking and the directional change. Results: Harmonic ratio was the only measure that resulted to be affected by directional changes and sampling frequency, decreasing with the presence of a directional change task. HR was affected in the AP and V directions for the 200 Hz, but only in AP direction for the 100 Hz group. Conclusion: Multiscale entropy, short term Lyapunov exponents and Recurrence quantification analysis were generally not affected by directional changes nor by sampling frequency, and could contribute to the definition of a fall risk index in free-walking conditions.
Many measures aiming to assess the stability of human motion have been proposed in the literature... more Many measures aiming to assess the stability of human motion have been proposed in the literature, but still there is no commonly accepted way to define or quantify locomotor stability. Among these measures, orbital stability analysis via Floquet multipliers is still under debate. Some of the controversies concerning the use of this technique could lie in the absence of a standard implementation. The aim of this study was to analyse the influence of i) experimental measurement noise, ii) variables selected for the construction of the state space, and iii) number of analysed cycles on the outputs of orbital stability applied to walking. The analysis was performed on a 2-dimensional 5-link walking model and on a sample of 10 subjects performing long over-ground walks. Noise resulting from stereophotogrammetric and accelerometric measurement systems was simulated in the in-silico analysis. Maximum Floquet multipliers resulted to be affected by both number of analysed strides and state space composition. The effect of experimental noise was found to be slightly more potentially critical when analysing stereophotogrammetric data then when dealing with acceleration data. Experimental and model results were comparable in terms of overall trend, but a difference was found in the influence of the number of analysed cycles.
Journal of Mechanics in Medicine and Biology, 2012
The aim of the present study was to identify the phases of gait and the joints where the \ground ... more The aim of the present study was to identify the phases of gait and the joints where the \ground reaction vector technique" (GRVT) can represent an acceptable alternative to the use of inverse dynamics (ID), when considering subjects with a lower-limb amputation. First, an analytical investigation of the ID of the three joints of the lower limb is given, distinguishing the gravitational, the inertial and the ground reaction contributions. The¯rst two contributions require inertial parameters estimation; for this purpose, literature anthropometric data are typically used, both for the unimpaired and prosthetic limb, as accurate speci¯c inertial parameters for the prosthetic limb are di±cult to obtain from companies or require time consuming estimation. This assumption potentially leads to errors in the three-dimensional (3D) joint moment estimation. Second, the results of two case studies, a trans-femoral amputee with two di®erent prostheses and Journal a trans-tibial amputee, showed that the GRVT can explain the most part of the net joint moment for the ankle and the knee in the whole stance phase, and for the hip in the¯rst part of the stance, leading to a similar clinical evaluation without any assumptions on inertial parameters.
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Papers by Rita Stagni