1,721,011 research outputs found
Balance and Motor Control in Dynamic Tasks
Full text linkNella prima parte dello studio si è descritto il mantenimento dell’equilibrio in seguito a perturbazioni indotte da stimoli esterni. La risposta posturale è stata analizzata dal punto di vista dinamico, cinematico ed elettromiografico, ottenendo una descrizione completa dei meccanismi adottati per contrastare la perdita di equilibrio. Vari parametri sono stati estratti dallo spostamento del centro di pressione e del centro di massa e sulla base dell’attività muscolare acquisita mediante elettromiografia di superficie, con lo scopo di ottenere indici che correlino con le diverse caratteristiche della perturbazione. Sulla base dei dati cinematici sono state descritte le strategie posturali adottate per contrastare la perturbazione indotta, allo scopo di quantificare se differenti condizioni perturbative facciano sorgere differenti risposte, che prevedono l’uso di differenti strategie articolari. Infine il controllo dell’equilibrio è stato descritto attraverso un modello a doppio pendolo inverso, attraverso tecniche che, sebbene ben note ed impiegate in altri ambiti, risultano poco usate per la descrizione della postura in condizioni dinamiche.
Nella seconda parte si è indagato il controllo della dinamica del cammino in termini di attività muscolare, acquisita su centinaia di passi consecutivi, permettendo un nuovo tipo di descrizione non basata solamente su parametri temporali ma anche sulla frequenza con cui ogni modalità di attivazione muscolare di presenta durante il cammino. I principali risultati includono la quantificazione dei pattern di co-contrazione dei flessori di caviglia e la loro ricorrenza durante il cammino. Si sono inoltre descritte le differenze legate al genere riguardanti l’attività dei principali muscoli dell’intero arto inferiore. Basandosi sui precedenti risultati si sono poi quantificate le differenze legate al genere nei pattern di co-contrazione degli antagonisti che regolano la meccanica dell’articolazione di caviglia durante il cammino.In the first part of this work a characterization of the upright stance recovery after balance perturbation administered through external stimuli was performed. Balance response has been analyzed in dynamics, kinematics and electromyographic terms, in order to obtain a complete description of which mechanisms are employed to withstand sudden stance perturbations. A series of parameters have been extracted from center of pressure and center of mass displacement and from electromyographic signals, acquired from lower limb and trunk muscles, in order to obtain a series of indexes which can correlate with the different characteristic of perturbations. From kinematic data, a description of the postural strategies adopted to withstand perturbations has been performed, in order to observe whether different perturbation conditions evoke different responses, employing different articular joints. Eventually, a first attempt to model perturbed upright stance through a double-link inverted pendulum is proposed, applying control systems seldom employed in describing this kind of dynamic motor task.
In the second part, the motor control during the walking task was described in terms of muscular activity. Myoelectric signals were acquired in hundreds of consecutive strides, obtaining a new type of description, not only in terms of temporal parameters of muscles activity but also in terms of the occurrence frequency of each muscular activation modality during gait. The main outcomes include the description of co-contraction activity between ankle flexor muscles and the assessment of the recurrence of each co-activation pattern during walking. Furthermore, a description of the whole lower limb muscles behavior was performed, aimed to the quantification of gender-based differences in muscular recruitment during gait. Then, these two aspects were joined in assessing gender-related differences in co-contraction activity of muscles which control the ankle joint mechanics during walking
Analisi statistica dell'attività mioelettrica del gastrocnemio laterale durante il cammimo
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Statistical Analysis of EMG Signal Acquired from Tibialis Anterior during Gait
No full textAim of the present study was to identify the different modalities of activation of tibialis anterior (TA) during gait at self-selected speed, by a statistical analysis of surface electromyographic signal from a large number (hundreds) of strides per subject. The analysis on ten healthy adults showed that TA is characterized by different activation modalities within different strides of the same walk. The most recurrent modality consists of three activations observed in 37.4±1.9% of total strides: at the beginning of gait cycle, around stance-to swing-transition and in the terminal swing. Further two modalities differ from the most recurrent one because of 1) the continuous activation during swing; 2) a further activity in the late mid-stance. The study of these different modalities of activation suggested that TA acts as pure ankle dorsi-flexor only in a small percentage (~20%) of total strides, where TA activity occurs in the simpler modality. The increase in the complexity of the recruitment of the muscle introduces an uncommon activity during mid-stance, which does not occur for the flexion of the ankle but is related to the activity of the TA as a foot invertor muscle
Assessment of the surface electromyographic activity of thigh muscles in males and females
No full textSurface electromyographic (sEMG) signal is commonly used as input information to control robotic systems. sEMG signals vary from person to person; gender is a factor influencing this variation. The aim of the study is to detect gender-related differences in sEMG activity of main three thigh muscles (rectus femoris, RF, biceps femoris, BF and vastus lateralis, VL) during walking at comfortable speed and cadence. Statistical analysis of sEMG signals, performed in seven male (M-group) and seven female (F-group) adults, showed clear gender-related differences in VL behavior and no relevant differences in the behavior of RF and BF. F-group, indeed, adopts a walking modality with a higher number of VL activations during gait cycle, compared to M-group. This suggests a female propensity for a more complex VL recruitment, during walking. This novel information suggests considering separate approaches for males and females, in providing electromyographic signals as input information to control robotic systems
Surface-EMG analysis for the quantification of thigh muscle dynamic co-contractions during normal gait
No full textThe research purpose was to quantify the co-contraction patterns of quadriceps femoris (QF) vs. hamstring muscles during free walking, in terms of variability of onset-offset muscular activation and occurrence frequency. Statistical Gait Analysis was performed on surface-EMG signals from vastus lateralis (VL), rectus femoris (RF), and medial hamstrings (MH), in 16315 strides walked by 30 healthy young adults. Results showed full superimpositions of MH with both VL and RF activity from terminal swing, 80 to 100% of gait cycle (GC), to the successive loading response (≈0-15% of GC), in around 90% of the considered strides. A further superimposition was detected during the push-off phase both between VL and MH activation intervals (38.6±12.8% to 44.1±9.6 % of GC) in 21.9±13.6% of strides, and between RF and MH activation intervals (45.9±5.3% to 50.7±9.7 of GC) in 32.7±15.1% of strides. These findings led to identify three different co-contractions among QF and hamstring muscles during able-bodied walking: in early stance, in push-off and during swing. This study represents the first attempt for developing a ‘‘normality'' reference frame for QF/MH co-contractions, able to include the physiological variability of the phenomenon
Assessment of the variability of vastii myoelectric activity in young healthy females during walking: A statistical gait analysis
No full textThe study was designed to assess the natural variability of the activation modalities of vastus medialis (VM) and vastus lateralis (VL) during walking at a self-selected speed and cadence of 30 young, healthy, females. This was achieved by conducting statistical gait analysis on the surface electromyographic signals from hundreds of strides for each subject. Results revealed variability in the number of activations, occurrence frequency, and onset-offset instants across the thousands of strides analyzed. However, despite the variability, there was one activation occurrence which remained consistent across subjects for both VM and VL. This occurred from terminal swing to the following loading response (observed in 100% of strides). A second, less frequent, activation occurred between mid-stance up to pre-swing (observed in 39.3 ± 22.4% of strides for VM and in 35.1 ± 20.6% for VL). No significant differences (p>. 0.05) were observed in the onset-offset instants or in the occurrence frequency, which suggest a simultaneous recruitment of VM and VL. This "normality" pattern represents the first attempt at developing a reference frame for vastii sEMG activity during walking, that is able to include the physiological variability of the phenomenon and control the confounding effects of age and gender
Inertial Sensing for Human Motion Analysis: Enabling Sensor-to-Body Calibration Through an Anatomical and Functional Combined Approach
No full textThe use of inertial measurement units is gaining attention to estimate human joint kinematics. However, to obtain clinically meaningful results, sensor frame needs to be aligned with the underlying anatomical one. Although during the years different approaches have been proposed, a common consensus has not been reached. Further, inertial sensor positioning on human segments can affect frame definition and kinematics estimation. Thus, the aim of the present work is to define an anatomical calibration procedure for lower limb joints kinematics, robust with respect to sensor misalignment, and based on a limited set of movements, with static and functional assumptions. To this purpose, straight walking and turning motor tasks in six healthy subjects were considered, and results were compared with those provided by an optoelectronic system. Three sensor placements have been also evaluated to test the procedure with respect to sensor positioning. After offset removal, an average RMSE ≤2.5 deg in gait, and ≤2 deg in turning for all the configurations were obtained, outperforming results from previous approaches. Average offset values resulted about 6 deg for hip and ankle, whereas negligible for the knee. Outcomes of this study enable a simple and accurate measurement of clinically meaningful joints kinematics, also without a strict sensor placement
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