Moving from laboratory to real life conditions: Influence on the assessment of variability and stability of gait

The availability of wearable sensors allows shifting gait analysis from the traditional laboratory settings, to daily life conditions. However, limited knowledge is available about whether alterations associated to different testing environment (e.g. indoor or outdoor) and walking protocols (e.g. free or controlled), result from actual differences in the motor behaviour of the tested subjects or from the sensitivity to these changes of the indexes adopted for the assessment. In this context, it was hypothesized that testing environment and walking protocols would not modify motor control stability in the gait of young healthy adults, who have a mature and structured gait pattern, but rather the variability of their motor pattern. To test this hypothesis, data from trunk and shank inertial sensors were collected from 19 young healthy participants during four walking tasks in different environments (indoor and outdoor) and in both controlled (i.e. following a predefined straight path) and free conditions. Results confirmed what hypothesized: variability indexes (Standard deviation, Coefficient of variation and Poincaré plots) were significantly influenced by both environment and walking conditions. Stability indexes (Harmonic ratio, Short term Lyapunov exponents, Recurrence quantification analysis and Sample entropy), on the contrary, did not highlight any change in the motor control. In conclusion, this study highlighted an influence of environment and testing condition on the assessment of specific characteristics of gait (i.e. variability and stability). In particular, for young healthy adults, both environment and testing conditions affect gait variability indexes, whereas neither affect gait stability indexes

Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Context. Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with coronal mass ejections (CMEs) and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20–90 MHz) is now possible with the Low Frequency Array (LOFAR), opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. Aims. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon. Methods. Thetype II shock source-positions and spectra were obtained using 91 simultaneous tied-array beams of LOFAR, and the CME was observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) and by the COR2A coronagraph of the SECCHI instruments on board the Solar Terrestrial Relation Observatory(STEREO). The 3D structure was inferred using triangulation of the coronographic observations. Coronal magnetic fields were obtained from a 3D magnetohydrodynamics (MHD) polytropic model using the photospheric fields measured by the Heliospheric Imager (HMI) on board the Solar Dynamic Observatory (SDO) as lower boundary. Results. The type II radio source of the coronal shock observed between 50 and 70 MHz was found to be located at the expanding flank of the CME, where the shock geometry is quasi-perpendicular with θBn ~ 70°. The type II radio burst showed first and second harmonic emission; the second harmonic source was cospatial with the first harmonic source to within the observational uncertainty. This suggests that radio wave propagation does not alter the apparent location of the harmonic source. The sources of the two split bands were also found to be cospatial within the observational uncertainty, in agreement with the interpretation that split bands are simultaneous radio emission from upstream and downstream of the shock front. The fast magnetosonic Mach number derived from this interpretation was found to lie in the range 1.3–1.5. The fast magnetosonic Mach numbers derived from modelling the CME and the coronal magnetic field around the type II source were found to lie in the range 1.4–1.6

Liquid crystals and their defects

These lecture notes discuss classical models of liquid crystals, and the different ways in which defects are described according to the different models.Comment: CIME lecture course, Cetraro, 201

Changes of human movement complexity during maturation: quantitative assessment using multiscale entropy

Movement complexity can be defined as the capability of using different strategies to accomplish a specific task and is expected to increase with maturation, reaching its highest level in adulthood.Multiscale Entropy (MSE) has been proposed to estimate complexity on different kinematic signals, at different time scales. When applied on trunk acceleration data during natural walking (NW) at different ages, MSE decreased from childhood to adulthood, apparently contradicting the premises. On the contrary, authors hypothesised that this decrease was dependent on the specific task analysed and resulted from the concurrent increase in gait automaticity.This work aims to test this hypothesis, applying MSE on a non-paradigmatic task (tandem walking, TW), in order to exclude aspects related to automaticity.MSE was estimated on trunk acceleration data, collected on children, adolescents, and young adults during TW and NW. As hypothesized, MSE increased significantly with age in TW and decreased in NW on the sagittal plane. Assuming the development of complexity in TW as reference, MSE in NW showed a reduction to half of the complexity of TW with maturation on the sagittal plane. These results indicate MSE as sensitive to differences in performance due to maturation and to expected changes in complexity related to the specific performed task

Complexity of human gait pattern at different ages assessed using multiscale entropy: From development to decline

Multiscale entropy (MSE) has been applied in biomechanics to evaluate gait stability during human gait and was found to be a promising method for evaluating fall risk in elderly and/or pathologic subjects. The hypothesis of this work is that gait complexity is a relevant parameter of gait development during life, decreasing from immature to mature gait and then increasing again during old age. In order to verify this hypothesis, MSE was applied on trunk acceleration data collected during gait of subjects of different ages: toddlers at the onset of walking, pre-scholar and scholar children, adolescents, young adults, adults and elderlies. MSE was estimated by calculating sample entropy (SEN) on raw unfiltered data of L5 acceleration along the three axes, using values of τ ranging from 1 to 6. In addition, other performance parameters (cadence, stride time variability and harmonic ratio) were evaluated. The results followed the hypothesized trend when MSE was applied on the vertical and/or anteroposterior axis of trunk acceleration: an age effect was found and adult SEN values were significantly different from children ones. From young adults to elderlies a slight increase in SEN values was shown although not statistically significant. While performance gait parameters showed adolescent gait similar to the one of adults, SEN highlighted that their gait maturation is not complete yet. In conclusion, present results suggest that the complexity of gait, evaluated on the sagittal plane, can be used as a characterizing parameter of the maturation of gait control

A non invasive protocol to estimate muscle tendon lengths and moment arms through ultrasound images

INTRODUCTION One of the important aspects of the application of muscle-skeletal models in clinical diagnostic is the possibility to estimate muscle force contributions to joint moments, taking into account muscle co-contraction and physiological aspects of muscles. An accurate representation of the lower limb musculoskeletal system is required for the prediction of the muscle-tendon forces during human movement when using these models. The most recent muscle skeletal models are still sensitive to musculoskeletal geometry. Usually muscle- tendon lengths and moment arms are estimated from joint angles using published data obtained from cadaver specimens of different heights [1,2]. The determination of the length and of the line of action of the muscles personalized to subject morphology is one of the major steps in the development of reliable musculoskeletal models. In 2007, a non-invasive method for determining the line of action of lower limb muscles with means of manual pointing on the subject has been proposed [3]. The aim of this study is to further improve the accuracy of these estimations using ultrasound images for identifying muscle insertions, origins and via points of a specific subject. CLINICAL SIGNIFICANCE Functional evaluation of muscle co-contraction patterns can significantly improve the clinical decision process. The reliability of musculoskeletal models for the quantification of muscle co-contraction patterns is critically affected by the limited possibility to adapt muscle models to subject-specific characteristics. The possibility to quantify in-vivo subject-specific muscle parameters can significantly improve the clinical applicability of musculoskeletal models. METHODS One healthy young subject [25y, 1.72m, 61kg] participated in the study. He was asked to perform an initial step exercise and then to continue walking at self-selected speed while kinematic data (SmartE, BTS, Milan, Italy) were collected. A 3-segment model of the subject right lower limb (thigh, leg and foot) was obtained. Gastrocnemius, soleus and tibialis anterior were selected as representative muscles of the lower limb. Origins (O), insertions (I) and via points of these muscles were calibrated using manual pointing [3] and using ultrasound images [4] while the participant was standing in neutral position. Retinaculum was calibrated both in neutral position and in complete dorsi-flexion of the ankle. These points were then reconstructed during the walk exercise. Muscle tendon lengths and moment arms were calculated through 5 different methods: i) using equations taken from literature [1,2]; ii) using IO points calibrated with manual pointing; iii) using IO points calibrated with ultrasound images. 266 In methods ii) and iii) tibialis anterior length and moment arm were calculated first with retinaculum calibrated with the ankle in neutral position (ii.a and iii.a) and then in complete dorsiflexion (ii.b and iii.b). RESULTS (1.a) (1.b) Figure 1: Tibialis anterior muscle-tendon length (1.a) and moment arms (1.b) obtained with different methods. Muscle tendon length variations obtained with the various methods were similar during the exercise. Offset values were underestimated or overestimated with the equation approach, while were comparable if obtained with kinematic or ultrasound IO calibrations. Moment arm results varied up to 40% of the mean values with the different estimation methods. In figure 1 exemplificative results for tibialis anterior during initial step and stance phases are shown. Tibialis anterior length and moment arm varied calibrating the retinaculum at different ankle position. DISCUSSION Results of this study showed the importance of calibrating insertion, origin and via point of muscles in order to build reliable muscle skeletal models. Different methods showed similar trend of muscle tendon lengths during the exercise, while absolute value varied of about 5%. Moment arm results showed between method d..