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This study focuses on the metrological characterization of a 3D vision system consisting in the fusion of a CMOS camera sensor with a 2D laser scanner for contactless dimensional measurements. The purpose is to obtain an enhanced measurement information as a result of the combination of two different data sources. On one side, we can estimate the pose of the target measurand by solving the well-known Perspective-n-Point (PnP) problem from the calibrated camera. On the other side, the 2D laser scanner generates a discrete point cloud which describes the profile of the intercepted surface of the same target object. This solution allows to estimate the target’s geometrical parameters through the application of fit-to-purpose algorithms that see the data acquired by the overall system as their input. The measurement uncertainty is evaluated by applying the Monte Carlo Method (MCM) to estimate the uncertainty deriving from the Probability Distribution Functions (PDF) of the input variables. Through a Design of Experiments (DOE) model the effects of different influence factors were evaluated.

This research focuses on the characterization of the metrology of Optical 3D Coordinate Measurement Systems (O3DCMS). The focus is set on the identification and execution of the procedure indicated by the currently active technical standards related to industrial O3DCMS, for their metrological assessment, objective comparison, and performance tracking. This work leads to the implementation of an ad hoc software for the execution of the standard tests by the ISO 10360-13 standard. The implemented software application is employed in a real-case scenario for evaluating the performances of an industrial 3D scanner based on structured light. The specific hardware components to be assessed are two light sources of the active stereoscopic vision system, named Digital Light Projectors (DLP). The case study applies the procedures and metrics indicated by the active standards to objectively compare two alternative hardware design of the system under test. This results in the identification of the most performing hardware configuration, allowing the selection of the best system design, basing on objective metrological parameters.

Whole-body vibration (WBV) may increase musculoskeletal disorder risk among workers standing on vibrating surfaces for prolonged periods. Limited studies were conducted to comprehend WBV impact on individuals engaged in dynamic activities. This study explored the effects of different horizontal WBV frequencies on gait parameters, lower limb kinematics, and the cognitive response of healthy subjects. Forty participants walked at constant speed on a treadmill mounted on a horizontal shaker providing harmonic vibration with an amplitude of 1 m/s 2 and frequencies 2-10 Hz, with inversely proportional amplitudes. A Psychomotor Vigilance Test measured reaction time while a motion capture system recorded walking kinematics. ANOVA results revealed no significant impact of vibration frequencies on the reaction time. At 2 Hz, alterations in gait spatiotemporal parameters were significant, with reduced stride length, stride time, step length, and stance time and increased step width and cadence. Similarly, gait variability measured by standard deviation and coefficient of variation significantly increased at 2 Hz compared to the other conditions. Comparably, kinematic time series analyzed through statistical parametric mapping showed significant adjustments in different portions of the gait cycle at 2 Hz, including increased hip abduction and flexion, greater knee flexion around the heel strike, and augmented ankle dorsiflexion. Participants exhibited gait kinematic variations, mainly at 2 Hz, where the associated mediolateral displacement was higher, as a plausible strategy to maintain stability and postural control during perturbed locomotion. These findings highlight individuals' complex biomechanical adaptations in response to horizontal WBV, especially at lower frequencies, under dual-task conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose : Alpine ski racing is a complex sport where no single factor can exclusively account for performance. We assessed body composition, using bioelectrical impedance vector analysis (BIVA), and our purpose was to study its influence on the strength and power profile of young alpine skiers. Methods : Anthropometric measurements and advanced BIVA parameters were recorded on eighteen alpine ski racers (6 females/12 males; 17.0 ± 1.3 years; 172.2 ± 9.3 cm; 68.5 ± 9.8 kg). Dynamic force and power were assessed using countermovement jumps (CMJ), while maximal isometric strength was evaluated for hip flexion-extension and abduction-adduction movements. Stepwise regression models examined the relationship between BIVA-derived parameters and strength/power variables. Results : Body cellular mass (BCM) positively related to jump height ( p  = .021, R 2  = 74%), jump momentum ( p  < .001, R 2  = 89%), reactive strength index modified ( p  = .026, R 2  = 75%) and peak concentric power ( p  < .001, R 2  = 82%), while intracellular water (ICW) related to peak eccentric ( p  < .001, R 2  = 76%) and concentric force ( p  < .001, R 2  = 77%) as well as to concentric rate of force development together with the phase angle (PhA) ( p  = .008, R 2  = 79% and R 2  = 0.015). Regarding isometric assessment, ICW was a significant predictor for all four movement directions, and PhA contributed to hip adduction strength. Conclusions : Body composition, particularly BCM and ICW, significantly predict force- and power-related factors in young alpine skiers.

Background: Physical activity may help prevent the development of adverse health disorders in children. Thus, it is fundamental to assess key physical skills, such as jumping and running, from an early age. Several studies proposed test batteries to evaluate these motor skills in preschoolers, but no research studied their association. Therefore, this study aimed to evaluate the relationship between jump performance, including force production parameters, and sprint performance in preschool children., Methods: Twenty-nine preschoolers, aged 4 to 5, underwent assessments, including countermovement jumps (CMJ) and standing long jumps (SLJ) on a force plate. Then they performed a 10-meter linear sprint assessed using photocells., Results: Regression models revealed that SLJ distance emerged as a significant predictor (R2=49.3%, P<0.001) of sprint horizontal velocity, while, for sprint momentum (R2=34.3%), both SLJ distance (P=0.004) and SLJ vertical peak force (P=0.036) were found to be significant predictors., Conclusions: The findings showed that short-distance (i.e., 10 m) linear sprint performance, both velocity and momentum, in preschoolers may be predicted mainly using SLJ assessment. These findings underscore the importance of early motor skill development in shaping physical abilities and their potential relationship in preschool children.

Lower-limb rehabilitation exoskeletons offer a transformative approach to enhancing recovery in patients with movement disorders affecting the lower extremities. This comprehensive systematic review delves into the literature on sensor technologies and the control strategies integrated into these exoskeletons, evaluating their capacity to address user needs and scrutinizing their structural designs regarding sensor distribution as well as control algorithms. The review examines various sensing modalities, including electromyography (EMG), force, displacement, and other innovative sensor types, employed in these devices to facilitate accurate and responsive motion control. Furthermore, the review explores the strengths and limitations of a diverse array of lower-limb rehabilitation-exoskeleton designs, highlighting areas of improvement and potential avenues for further development. In addition, the review investigates the latest control algorithms and analysis methods that have been utilized in conjunction with these sensor systems to optimize exoskeleton performance and ensure safe and effective user interactions. By building a deeper understanding of the diverse sensor technologies and monitoring systems, this review aims to contribute to the ongoing advancement of lower-limb rehabilitation exoskeletons, ultimately improving the quality of life for patients with mobility impairments.

This study compared the relative performance of alternative frequency weightings of hand-transmitted vibration (HTV) to predict the extent of cold-induced vasoconstriction in the digital arteries of HTV workers. The cold response of digital arteries was related to measures of daily vibration exposure expressed in terms of r.m.s. acceleration magnitude normalised to an 8-h day, frequency weighted according to either the frequency weighting W h defined in international standard ISO 5349-1:2001 (A h (8) in ms -2 r.m.s.) or the hand-arm vascular frequency weighting W p proposed in the ISO Technical Report 18570:2007 (A p (8) in ms -2 r.m.s.). The measure of daily vibration exposure constructed with the frequency weighting W p (A p (8)) was a better predictor of the cold response of the digital arteries in the HTV workers than the metric derived from the conventional ISO frequency weighting W h (A h (8)). This finding suggests that a measure of daily vibration exposure constructed with the vascular weighting W p , which gives more weight to intermediate- and high-frequency vibration (31.5-250 Hz), performed better for the prediction of cold induced digital arterial hyperresponsiveness than that obtained with the frequency weighting W h recommended in ISO 5349-1 which gives more importance to lower frequency vibration (≤16 Hz).

This study aims to investigate the effect of whole-body vibration along different axes on the response time (RT) of standing subjects during a customised psychomotor vigilance task (PVT). Twenty-five subjects were exposed to harmonic vibration with amplitude of 0.7 m/s 2 RMS and frequencies between 1.5 Hz and 12.5 Hz. ANOVA was used to assess if the difference of RT with and without vibration had a statistical relevance. Results showed that the RT was statistically affected by the vibration only at frequencies below 2 Hz. The vibration at higher frequencies had a minor effect on the RT. The RTs during the vibration exposure was, on average, 15% higher than the RT post exposure. Practitioner summary: This study investigates the effects of whole-body vibration (WBV) along different axes on the response time (RT). We measured the RTs to a psychomotor vigilance task of 25 standing subject exposed to WBV. The cognitive response was statistically affected by the WBV and, on average RT have increased of 15%.

During the secondary production of aluminum, upon melting the scrap in a furnace, there is the possibility of developing an aluminothermic reaction, which produces oxides in the molten metal bath. Aluminum oxides must be identified and removed from the bath, as they modify the chemical composition and reduce the purity of the product. Furthermore, accurate measurement of molten aluminum level in a casting furnace is crucial to obtain an optimal liquid metal flow rate which influences the final product quality and process efficiency. This paper proposes methods for the identification of aluminothermic reactions and molten aluminum levels in aluminum furnaces. An RGB Camera was used to acquire video from the furnace interior, and computer vision algorithms were developed to identify the aluminothermic reaction and melt level. The algorithms were developed to process the image frames of video acquired from the furnace. Results showed that the proposed system allowed the online identification of the aluminothermic reaction and the molten aluminum level present inside the furnace at a computation time of 0.7 s and 0.4 s per frame, respectively. The advantages and limitations of the different algorithms are presented and discussed.

Background: Step ascent and descent is one of the most common daily tasks. Although it is generally considered a rather simple movement, it may not be so easy for participants with Down syndrome., Methods: A kinematic analysis of step ascent and descent was conducted, and a comparison between 11 adult participants with Down syndrome and 23 healthy participants was carried out. This analysis was accompanied by a posturographic analysis with the aim of evaluating aspects relating to balance. The principal aim of postural control was to investigate the trajectory of the centre of pressure, while the kinematic analysis of movement included the following: (1) the analysis of anticipatory postural adjustments, (2) the calculation of spatiotemporal parameters and (3) the evaluation of articular range of motion., Results: A general instability for participants with Down syndrome, highlighted in the postural control by an increased anteroposterior and mediolateral excursion, when the test was conducted with both open and closed eyes, was found out. Regarding anticipatory postural adjustments, this deficit in balance control was revealed by the execution of small steps before completing the movement and by a much longer preparation time anticipating the movement. In addition, the kinematic analysis reported a longer ascent and descent time and a lower velocity, accompanied by a greater rising of both limbs in ascent, which indicates an increased perception of the obstacle. Finally, a wider trunk range of motion in both the sagittal and frontal planes was revealed., Conclusions: All the data confirm a compromised balance control that could be associated with damage to the sensorimotor centre., (© 2023 The Authors. Journal of Intellectual Disability Research published by MENCAP and International Association of the Scientific Study of Intellectual and Developmental Disabilities and John Wiley & Sons Ltd.)

Quality inspection in the industrial production field is experiencing a strong technological development that benefits from the combination of vision-based techniques with artificial intelligence algorithms. This paper initially addresses the problem of defect identification for circularly symmetric mechanical components, characterized by the presence of periodic elements. In the specific case of knurled washers, we compare the performances of a standard algorithm for the analysis of grey-scale image with a Deep Learning (DL) approach. The standard algorithm is based on the extraction of pseudo-signals derived from the conversion of the grey scale image of concentric annuli. In the DL approach, the component inspection is shifted from the entire sample to specific areas repeated along the object profile where the defect may occur. The standard algorithm provides better results in terms of accuracy and computational time with respect to the DL approach. Nevertheless, DL reaches accuracy higher than 99% when performance is evaluated targeting the identification of damaged teeth. The possibility of extending the methods and the results to other circularly symmetrical components is analyzed and discussed.

Background: The primary aim of this study was to assess how different conformations of the foot in individuals with Down syndrome affected the CoP during walking, and the secondary aim was to evaluate the effect of an excess of mass in young adults and children with Down syndrome and flat foot. The greater investigation of these aspects will allow for more targeted rehabilitation treatments to improve a patient's quality of life., Methods: The tests were carried out on 217 subjects with Down syndrome, 65 children and 152 young adults, and on 30 healthy individuals, 19 children and 11 young adults. All subjects underwent gait analysis, and the group with Down syndrome was also assessed with baropodometric tests to evaluate foot morphology., Results: The statistical analysis showed that within both the young adult and child groups, the CoP pattern in the anterior-posterior direction reflected a difficulty in proceeding in the walking direction compensated by a medio-lateral swing. The gait of children with Down syndrome was more impaired than that of young adults. In both young adults and children, a higher severity of impairment was found in overweight and obese female individuals., Conclusions: These results suggest that the sensory deficits and the development of hypotonic muscles and lax ligaments of the syndrome lead to morphological alterations of the foot that, combined with the physical characteristics of short stature and obesity, negatively impact the CoP pattern of people with Down syndrome during walking.

Recent developments in 3D graphic technologies enable the affordable and precise reconstruction of body scanned models that can be applied in a variety of verticals, such as fashion, fitness and wellness, and healthcare. The accuracy of body measurements is a crucial element for the successful application of avatars in the following use cases: Avatars that go beyond visual representation and offer intrinsic and precise anthropometric data defined as a smart body are discussed in this paper. In particular, this paper presents the Gate technology, an innovative, autonomous, sustainable body scanner, coupled with an automatic production pipeline and the concept of avatars as smart bodies. We present an accuracy study of scanning technology for scanning inanimate objects, as well as body parts versus the ground, by using an established accuracy scanning system. The results appear to be promising and confirm the hypothesis of applying the technology to the use cases discussed as well as broadening the research to other studies and future applications., Competing Interests: Conflict of interestsThe authors declare that they have no conflict of interest., (© The Author(s) 2022.)

Background: the primary aim of this study is to analyse the energy parameters of patients with Down syndrome compared to a control group and secondly to verify whether the sport activity leads to differences in energy expenditure., Methods: 3 groups of subjects were identified: 8 healthy subjects and 147 subjects with Down syndrome, of whom 14 played sports at least once a week. An energy index was calculated, given by the ratio between potential and kinetic energy. Next, kinetic ad potential energy parameters were extrapolated at 60% of the gait cycle (propulsion phase)., Findings: Down syndrome group was compared with the control group and emerged that the energy index was higher in the first one. No changes were found between Down syndrome and Down syndrome Sport groups. The analysis of the energy parameters showed that all parameters, except the medio-lateral kinetic energy, were higher in the control than in the Down syndrome groups. The potential energy, medio-lateral kinetic energy, and vertical were higher in the Down syndrome Sport group than in the Down syndrome group. The kinetic energy and the mean velocity were higher in the control group than in Down syndrome Sport group while the medio-lateral kinetic energy was lower., Interpretation: sport modified the parameter of potential energy but not that of kinetic energy, which continued to be different compared to the healthy group and increased the oscillations in the medio-lateral plane, which were double compared to Down syndrome group. The increase in potential energy, found to be almost equal to that of control group, indicates an increase in vertical oscillations. This could be because subjects who practise sports have stronger muscles that allow a greater push-off ability, which therefore increases their potential energy., Competing Interests: The authors declare no conflict of interest., (© 2022 Published by Elsevier Ltd.)

Background Cervical dystonia is a movement disorder characterized by involuntary and sustained contraction of the neck muscles that determines abnormal posture. The aim of this study was to investigate whether dystonic posture in patients with cervical dystonia affects walking and causes postural changes. Methods Patients with cervical dystonia and a group of age-matched healthy controls underwent an instrumental evaluation of the Timed Up and Go Test. Findings All the spatio-temporal parameters of the sub-phases of the Timed up and go test had a significantly higher duration in cervical dystonia patients compared to the control group while no differences in flection and extension angular amplitudes were observed. Indeed, we found that Cervical Dystonia patients had abnormalities in turning, as well as in standing-up and sitting-down from a chair during the Timed up and go test than healthy controls. Interpretation Impairment in postural control in cervical dystonia patients during walking and postural changes prompts to develop rehabilitation strategies to improve postural stability and reduce the risk of fall in these patients., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Nowadays, the use of wearable inertial-based systems together with machine learning methods opens new pathways to assess athletes' performance. In this paper, we developed a neural network-based approach for the estimation of the Ground Reaction Forces (GRFs) and the three-dimensional knee joint moments during the first landing phase of the Vertical Drop Jump. Data were simultaneously recorded from three commercial inertial units and an optoelectronic system during the execution of 112 jumps performed by 11 healthy participants. Data were processed and sorted to obtain a time-matched dataset, and a non-linear autoregressive with external input neural network was implemented in Matlab. The network was trained through a train-test split technique, and performance was evaluated in terms of Root Mean Square Error (RMSE). The network was able to estimate the time course of GRFs and joint moments with a mean RMSE of 0.02 N/kg and 0.04 N·m/kg, respectively. Despite the comparatively restricted data set and slight boundary errors, the results supported the use of the developed method to estimate joint kinetics, opening a new perspective for the development of an in-field analysis method.

This case study was designed starting from our experience at CYBATHLON 2020. The specific aim of this work was to compare the effectiveness of different fatigue reducing stimulation strategies during cycling induced by Functional Electrical Stimulation (FES). The compared stimulation strategies were: traditional constant frequency trains (CFTs) at 30 and 40Hz, doublet frequency trains (DFTs) and spatially distributed sequential stimulation (SDSS) on the quadriceps muscles. One Spinal Cord Injured (SCI) subject (39 years, T5-T6, male, ASIA A) was involved in 12 experimental sessions during which the four strategies were tested in a randomized order during FES-induced cycling performed on a passive trike at a constant cadence of 35 RPM. FES was delivered to four muscle groups (quadriceps, gluteal muscles, hamstrings and gastrocnemius) for each leg. The performance was evaluated in terms of saturation time (i.e., the time elapsed from the beginning of the stimulation until the predetermined maximum value of current amplitude is reached) and root mean square error (RMSE) of the actual cadence with respect to the target value. SDSS achieved a statistical lower saturation time and a qualitative higher RMSE of the cadence with respect to CFTs both at 30 and 40Hz.Clinical relevance- Conversely to previous literature, SDSS seems to be ineffective to reduce muscle fatigue during FES-induced cycling. Further experiments are needed to confirm this result.

Background: Vertical whole-body vibration (vWBV) during work, recreation, and transportation can have detrimental effects on physical and mental health. Studies have shown that lateral vibration at low frequencies (<3 Hz) can result in changes to spatiotemporal gait parameters. There are few studies which explore spatiotemporal gait changes due to vertical vibration at higher frequencies (> 3 Hz). This study seeks to assess the effect of vWBV on spatiotemporal gait parameters at a greater range of frequencies (≤ 30 Hz)., Methods: Stride Frequency (SF), Stride Length (SL), and Center of Pressure velocity (CoPv) was measured in seven male subjects (23 ± 4 years, 1.79 ± 0.05 m, 73.9 ± 9.7 kg) during In-Place Walking and nine male subjects (29 ± 7 years, 1.78 ± 0.07 m, 77.8 ± 9.9 kg; mean ± SD) during Treadmill Walking while exposed to vWBV. Load cells measured ground reaction forces during In-Place Walking and sensorized insoles acquired under-foot pressure during Treadmill Walking. Statistical tests included a one-way repeated-measures ANOVA, post-hoc two way paired T-tests, statistical power (1-β), correlation (R 2 ), and effect size (Cohen's d)., Results: While statistical significance was not found for changes in SF, SL, or Mean CoPv, small to large effects were found in all measured spatiotemporal parameters of both setups. During Treadmill Walking, vWBV was correlated with a decrease in SF (R 2  = 0.925), an increase in SL (R 2  = 0.908), and an increase in Mean CoPv (R 2  = 0.921) and Max CoPv (R 2  = 0.952) with a significant increase (p < 0.0083) in Max CoPv at frequencies of 8 Hz and higher., Significance: Study results demonstrated that vWBV influences spatiotemporal gait parameters at frequencies greater than previously studied., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Modelling the foot-ankle system (FAS) while exposed to foot-transmitted vibration (FTV) is essential for designing inhibition methods to prevent the effects of vibration-induced white-foot. K-means analysis was conducted on a data set containing vibration transmissibility from the floor to 24 anatomical locations on the right foot of 21 participants. The K-means analysis found three locations to be sufficient for summarising the FTV response. A three segment, four degrees-of-freedom lumped parameter model of the FAS was designed to model the transmissibility response at three locations when exposed to vertical vibration from 10 to 60 Hz. Reasonable results were found at the ankle, midfoot, and toes in the natural standing position (mean-squared error ( ε ) = 0.471, 0.089, 0.047) and forward centre of pressure (COP) ( ε  = 0.539, 0.058, 0.057). However, when the COP is backward, the model does not sufficiently capture the transmissibility response at the ankle ( ε  = 1.09, 0.219, 0.039). Practitioner summary The vibration transmissibility response of the foot-ankle system (FAS) was modelled with varying centre of pressure (COP) locations. Modelling the FAS using three transmissibility locations and two foot segments (rearfoot and forefoot) demonstrated reasonable results in a natural standing and forward COP position to test future intervention strategies. Abbreviations: COP: centre of pressure; DOF: degrees-of-freedom; FAS: foot-ankle system; FTV: foot-transmitted vibration; HAVS: hand-arm vibration syndrome; LDV: laser Doppler vibrometer; LP: lumped-parameter; VWT: vibration-induced white-toes; WBV: whole-body vibration.

Background: The etiology of Anterior Cruciate Ligament (ACL) injury in women football results from the interaction of several extrinsic and intrinsic risk factors. Extrinsic factors change dynamically, also due to fatigue. However, existing biomechanical findings concerning the impact of fatigue on the risk of ACL injuries remains inconsistent. We hypothesized that fatigue induced by acute workload in short and intense game periods, might in either of two ways: by pushing lower limbs mechanics toward a pattern close to injury mechanism, or alternatively by inducing opposed protective compensatory adjustments., Aim: In this study, we aimed at assessing the extent to which fatigue impact on joints kinematics and kinetics while performing repeated changes of direction (CoDs) in the light of the ACL risk factors., Methods: This was an observational, cross-sectional associative study. Twenty female players (age: 20-31 years, 1st-2nd Italian division) performed a continuous shuttle run test (5-m) involving repeated 180°-CoDs until exhaustion. During the whole test, 3D kinematics and ground reaction forces were used to compute lower limb joints angles and internal moments. Measures of exercise internal load were: peak post-exercise blood lactate concentration, heart rate (HR) and perceived exertion. Continuous linear correlations between kinematics/kinetics waveforms (during the ground contact phase of the pivoting limb) and the number of consecutive CoD were computed during the exercise using a Statistical Parametric Mapping (SPM) approach., Results: The test lasted 153 ± 72 s, with a rate of 14 ± 2 CoDs/min. Participants reached 95% of maximum HR and a peak lactate concentration of 11.2 ± 2.8 mmol/L. Exercise duration was inversely related to lactate concentration ( r = -0.517, p < 0.01), while neither%HR max nor [La - ] b nor RPE were correlated with test duration before exhaustion ( p > 0.05). Alterations in lower limb kinematics were found in 100%, and in lower limb kinetics in 85% of the players. The most common kinematic pattern was a concurrent progressive reduction in hip and knee flexion angle at initial contact (10 players); 5 of them also showed a significantly more adducted hip. Knee extension moment decreased in 8, knee valgus moment increased in 5 players. A subset of participants showed a drift of pivoting limb kinematics that matches the known ACL injury mechanism; other players displayed less definite or even opposed behaviors., Discussion: Players exhibited different strategies to cope with repeated CoDs, ranging from protective to potentially dangerous behaviors. While the latter was not a univocal effect, it reinforces the importance of individual biomechanical assessment when coping with fatigue., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Zago, David, Bertozzi, Brunetti, Gatti, Salaorni, Tarabini, Galvani, Sforza and Galli.)

A promising but still scarcely explored strategy for the estimation of gait parameters based on inertial sensors involves the adoption of machine learning techniques. However, existing approaches are reliable only for specific conditions, inertial measurements unit (IMU) placement on the body, protocols, or when combined with additional devices. In this paper, we tested an alternative gait-events estimation approach which is fully data-driven and does not rely on a priori models or assumptions. High-frequency (512 Hz) data from a commercial inertial unit were recorded during 500 steps performed by 40 healthy participants. Sensors' readings were synchronized with a reference ground reaction force system to determine initial/terminal contacts. Then, we extracted a set of features from windowed data labeled according to the reference. Two gray-box approaches were evaluated: (1) classifiers (decision trees) returning the presence of a gait event in each time window and (2) a classifier discriminating between stance and swing phases. Both outputs were submitted to a deterministic algorithm correcting spurious clusters of predictions. The stance vs. swing approach estimated the stride time duration with an average error lower than 20 ms and confidence bounds between ±50 ms. These figures are suitable to detect clinically meaningful differences across different populations., Competing Interests: The authors declare no conflicts of interest.

Whole-Body Vibration (WBV) is an occupational hazard affecting employees working with transportation, construction or heavy machinery. To minimize vibration-induced pathologies, ISO identified WBV exposure limits based on vibration transmissibility and apparent mass studies. The ISO guidelines do not account for variations in posture or movement. In our study, we measured the transmissibility and apparent mass at the mouth, lower back, and leg of participants during stationary and propelled walking. Stationary walking transmissibility was significantly higher at the lumbar spine and bite bar at 5 and 10 Hz compared to all higher frequencies while the distal tibia was lower at 5 Hz compared to 10 and 15 Hz. Propelled walking transmissibility was significantly higher at the bite bar and knee at 2 Hz than all higher frequencies. These results vary from previously published transmissibility values for static participants, showing that ISO standards should be adjusted for active workers., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The design of markerless systems to reconstruct human motion in a timely, unobtrusive and externally valid manner is still an open challenge. Artificial intelligence algorithms based on automatic landmarks identification on video images opened to a new approach, potentially e-viable with low-cost hardware. OpenPose is a library that t using a two-branch convolutional neural network allows for the recognition of skeletons in the scene. Although OpenPose-based solutions are spreading, their metrological performances relative to video setup are still largely unexplored. This paper aimed at validating a two-cameras OpenPose-based markerless system for gait analysis, considering its accuracy relative to three factors: cameras' relative distance, gait direction and video resolution. Two volunteers performed a walking test within a gait analysis laboratory. A marker-based optical motion capture system was taken as a reference. Procedures involved: calibration of the stereoscopic system; acquisition of video recordings, simultaneously with the reference marker-based system; video processing within OpenPose to extract the subject's skeleton; videos synchronization; triangulation of the skeletons in the two videos to obtain the 3D coordinates of the joints. Two set of parameters were considered for the accuracy assessment: errors in trajectory reconstruction and error in selected gait space-temporal parameters (step length, swing and stance time). The lowest error in trajectories (~20 mm) was obtained with cameras 1.8 m apart, highest resolution and straight gait, and the highest (~60 mm) with the 1.0 m, low resolution and diagonal gait configuration. The OpenPose-based system tended to underestimate step length of about 1.5 cm, while no systematic biases were found for swing/stance time. Step length significantly changed according to gait direction ( p = 0.008), camera distance ( p = 0.020), and resolution ( p < 0.001). Among stance and swing times, the lowest errors (0.02 and 0.05 s for stance and swing, respectively) were obtained with the 1 m, highest resolution and straight gait configuration. These findings confirm the feasibility of tracking kinematics and gait parameters of a single subject in a 3D space using two low-cost webcams and the OpenPose engine. In particular, the maximization of cameras distance and video resolution enabled to achieve the highest metrological performances., (Copyright © 2020 Zago, Luzzago, Marangoni, De Cecco, Tarabini and Galli.)

Quantifying the response of postural control in developmental athletes makes it possible to understand critical coordination and learning phases and to improve technical-physical interventions. However, the influence of maturation on postural control amongst young soccer players has neither been tested using quantitative methods, nor over a wide age range. In this study, we examined stabilometric parameters of 238 young male soccer players from 9 to 17 years old relative to maturity offset. Two 30-s tests (eyes open and eyes closed) were recorded on a baropodometric platform at 50 Hz. Participants were split into six groups according to their maturity offset, expressed as years from individual's peak height velocity. Dependent variables were: Sway Area, Center-of-Pressure velocity, standard deviation of the antero-posterior and medio-lateral Center-of-Pressure trajectory, Romberg Quotient. Sway Area was significantly higher in players with maturity offset <-1.5 than in groups with maturity offset > 0.5 years (p < 0.001, large effect). Center-of-Pressure velocity markedly dropped in players with maturity offset >-0.5 years (p < 0.001, very large effect). Antero-posterior standard deviation was higher before than after peak height velocity (p < 0.05, large effect) and significantly higher with closed eyes at some points. Medio-lateral standard deviation was higher in the youngest group of players (maturity offset <-2.5 years, large effect) than in those with maturity offset >-0.5 years. In sum, stabilometric parameters improved with age until zero maturity offset was achieved. Thereafter, variables describing postural control in developing soccer players were almost stable. No evidence of a changing role of vision in postural sway control during maturation was observed., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Workers in mining, mills, construction and some types of manufacturing are exposed to vibration that enters the body through the feet. Exposure to foot-transmitted vibration (FTV) is associated with an increased risk of developing vibration-induced white foot (VIWFt). VIWFt is a vascular and neurological condition of the lower limb, leading to blanching in the toes and numbness and tingling in the feet, which can be disabling for the worker. This paper presents a two-dimensional dynamic model describing the response of the foot-ankle system to vibration using four segments and eight Kelvin-Voigt models. The parameters of the model have been obtained by minimizing the quadratic reconstruction error between the experimental and numerical curves of the transmissibility and the apparent mass of participants standing in a neutral position. The average transmissibility at five locations on the foot has been optimized by minimizing the difference between experimental data and the model prediction between 10 and 100 Hz. The same procedure has been repeated to fit the apparent mass measured at the driving point in a frequency range between 2 and 20 Hz. Monte Carlo simulations were used to assess how the variability of the mass, stiffness and damping matrices affect the overall data dispersion. Results showed that the 7°-of-freedom model correctly described the transmissibility: the average transmissibility modulus error was 0.1. The error increased when fitting the transmissibility and apparent mass curves: the average modulus error was 0.3. However, the obtained values were reasonable with respect to the average inter-participant variability experimentally estimated at 0.52 for the modulus. Study results can contribute to the development of materials and equipment to attenuate FTV and, consequently, lower the risk of developing VIWFt., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Vibration-white foot as an occupational disease has underscored the need to better understand the vibration response of the foot. While vibration transmissibility data exist for a natural standing position, it is anticipated that weight distribution will affect the response. The purpose of this study was to determine the effects of changes in centre of pressure (COP) on the foot's biomechanical response. Twenty-one participants were exposed to vertical vibration of 30 mm/s, with a sine sweep from 10-200 Hz. Z -axis (vertical) vibration was measured at 24 locations on the right foot, with the COP shifted forward or toward the heel. A mixed model analysis at each location revealed significant differences ( p  < .001) in the transmissibility response when the COP was altered to the forefoot and rearfoot. In general, the peak frequency of the average vibration response increased for a region of the foot when the COP was shifted toward that region. Practitioner Summary : Altering the centre of pressure location resulted in changes in the transmission of vibration through the foot. The forward lean position was associated with the greatest amplitude of vibration transmissibility at the toes. This information is relevant for clinicians studying vibration-induced white-foot and engineers designing protective equipment.

Changes of directions and cutting maneuvers, including 180-degree turns, are common locomotor actions in team sports, implying high mechanical load. While the mechanics and neurophysiology of turns have been extensively studied in laboratory conditions, modern inertial measurement units allow us to monitor athletes directly on the field. In this study, we applied four supervised machine learning techniques (linear regression, support vector regression/machine, boosted decision trees and artificial neural networks) to predict turn direction, speed (before/after turn) and the related positive/negative mechanical work. Reference values were computed using an optical motion capture system. We collected data from 13 elite female soccer players performing a shuttle run test, wearing a six-axes inertial sensor at the pelvis level. A set of 18 features (predictors) were obtained from accelerometers, gyroscopes and barometer readings. Turn direction classification returned good results (accuracy > 98.4%) with all methods. Support vector regression and neural networks obtained the best performance in the estimation of positive/negative mechanical work (coefficient of determination R 2 = 0.42-0.43, mean absolute error = 1.14-1.41 J) and running speed before/after the turns (R 2 = 0.66-0.69, mean absolute error = 0.15-018 m/s). Although models can be extended to different angles, we showed that meaningful information on turn kinematics and energetics can be obtained from inertial units with a data-driven approach.

Exposure to foot-transmitted vibration (FTV) can lead to pain and numbness in the toes and feet, increased cold sensitivity, blanching in the toes, and joint pain. Prolonged exposure can result in a clinical diagnosis of vibration-induced white foot (VIWFt). Data on the biomechanical response of the feet to FTV is limited; therefore, this study seeks to identify resonant frequencies for different anatomical locations on the human foot, while standing in a natural position. A laser Doppler vibrometer was used to measure vertical (z-axis) vibration on 21 participants at 24 anatomical locations on the right foot during exposure to a sine sweep from 10-200 Hz with a peak vertical velocity of 30 mm/s. The most notable differences in the average peak frequency occur between the toes (range: 99-147 Hz), midfoot (range: 51-84 Hz) and ankle (range: 16-39 Hz). Practitioner Summary: The biomechanical response of the human foot exposed to foot-transmitted vibration, when standing in a natural position, was measured for 21 participants. The foot does not respond uniformly; the toes, midfoot, and ankle regions need to be considered independently in future development of isolation strategies and protective measures.

Objective: (i) to determine the outcomes of whole-body vibration training (WBVT) on obese individuals, and the intervention settings producing such effects; (ii) identify potential improper or harmful use of WBVT., Design: Systematic review., Data Sources: Medline, Scopus, Web of Science, PEDro and Scielo until July 2018., Eligibility Criteria: Full papers evaluating the effect of WBVT on body composition, cardiovascular status and functional performance in obese adults. Papers with PEDro score<4 were excluded., Study Appraisal and Synthesis: Risk of bias and quality of WBVT reporting were assessed with PEDro scale (randomized controlled trials) or TREND checklist (non-randomized studies) and a 14-items checklist, respectively. Weighted acceleration, daily exposure and Hedges' adjusted g were computed., Results: We included 18 papers published 2010-2017. Typical interventions consisted in three sessions/week of exercises (squats, calf-raises) performed on platforms vibrating at 25-40 Hz (amplitude: 1-2 mm); according to ISO 2631-1:1997, daily exposure was "unsafe" in 7/18 studies. Interventions lasting ≥6 weeks improved cardiac autonomic function and reduced central/peripheral arterial stiffness in obese women; 10 weeks of WBVT produced significant weight/fat mass reduction, leg strength improvements as resistance training, and enhanced glucose regulation when added to hypocaloric diet. No paper evidenced losses of lean mass. Isolated cases of adverse effects were reported., Summary: To date, WBVT is a promising adjuvant intervention therapy for obese women; long-term studies involving larger cohorts and male participants are required to demonstrate the associated safety and health benefits. The therapeutic use of WBVT in the management of obese patients is still not standardised and should be supported by an extensive knowledge on the causality between vibration parameters and outcomes., Competing Interests: The authors have declared that no competing interests exist.

Background: Participation rates in extreme sports have grown exponentially in the last 40 yr, often surpassing traditional sporting activities. The purpose of this study was to examine injury rates in foot-launched flying sports, i.e., sports in which a pilot foot-launches into flight with a wing already deployed., Methods: This paper is based on a retrospective analysis of the reports of incidents that occurred between 2000 and 2014 among the British Hang Gliding and Paragliding Association members., Results: The majority of the 1411 reported injuries were in the lower limb, followed by the upper limb. The most common lower limb injury was to the ankle and included fractures, sprains, and dislocations. The distribution of injures was different in each discipline. The calculated yearly fatality rate (fatalities/100,000 participants) was 40.4 in hang gliding, 47.1 in paragliding, 61.9 in powered hang gliding and 83.4 in powered paragliding; the overall value for foot-launched flight sports was 43.9., Discussion: Significant differences in injury rates and injury patterns were found among different sport disciplines that can be useful to steer research on safety, and adopt specific safety rules about flying, protective clothing and safety systems in each of these sports.Feletti F, Aliverti A, Henjum M, Tarabini M, Brymer E. Incidents and injuries in foot-launched flying extreme sports. Aerosp Med Hum Perform. 2017; 88(11):1016-1023.

This paper describes the experimental characterisation of the apparent mass matrix of eight male subjects in standing position and the identification of nonlinearities under both mono-axial and dual-axis whole-body vibration. The nonlinear behaviour of the response was studied using the conditioned response techniques considering models of increasing complexity. Results showed that the cross-axis terms are comparable to the diagonal terms. The contribution of the nonlinear effects are minor and can be endorsed to the change of modal parameters during the tests. The nonlinearity generated by the vibration magnitude is more evident in the subject response, since magnitude-dependent effects in the population are overlaid by the scatter in the subjects' biometric data. The biodynamic response is influenced by the addition of a secondary vibration axis and, in case of dual-axis vibrations, the overall magnitude has a marginal contribution. Practitioner Summary: We have measured both the diagonal and cross-axis elements of the apparent mass matrix. The effect of nonlinearities and the simultaneous presence of vibration along two axes are smaller than the inter-subject variability.

This study investigates the whole-body vibration exposure in kite surfing, alpine skiing, snowboarding and cycling. The vibration exposure was experimentally evaluated following the ISO 2631 guidelines. Results evidenced that the most critical axis is the vertical one. The weighted vibration levels are always larger than 2.5 m/s(2) and the vibration dose values are larger than 25 m/s(1.75). The exposure limit values of the EU directive are reached after 8-37 min depending on the sport. The vibration magnitude is influenced by the athletes' speed, by their skill level and sometimes by the equipment. The large vibration values suggest that the practice of sport activities may be a confounding factor in the aetiology of vibration-related diseases., Practitioner Summary: The vibration exposure in some sports is expected to be large, but has never been quantified in the literature. Results of experiments performed in cycling, alpine and water sports outlined vibration levels exceeding the EU standard limit values.

The human response to vibration is typically studied using linear estimators of the frequency response function, although different literature works evidenced the presence of non-linear effects in whole-body vibration response. This paper analyses the apparent mass of standing subjects using the conditioned response techniques in order to understand the causes of the non-linear behaviour. The conditioned apparent masses were derived considering models of increasing complexity. The multiple coherence function was used as a figure of merit for the comparison between the linear and the non-linear models. The apparent mass of eight male subjects was studied in six configurations (combinations of three vibration magnitudes and two postures). The contribution of the non-linear terms was negligible and was endorsed to the change of modal parameters during the test. Since the effect of the inter-subject variability was larger than that due to the increase in vibration magnitude, the biodynamic response should be more meaningfully modelled using a linear estimator with uncertainty rather than looking for a non-linear modelling.

This study was carried out to investigate the influence of the body posture and of the foot support on the apparent mass distribution at the feet of standing subjects exposed to whole-body vibration. The apparent mass was measured at the driving point through a capacitive pressure sensor matrix, which allowed to separate the contributions of the different foot regions. The overall value was also determined using a conventional measurement system based on piezoelectric load cells. Ten male subjects performed 15 tests with three kinds of feet supports (flat rigid, anatomic rigid and flat soft) in five different postures. Static components of the pressure measurements were exploited to identify which fraction of the weight is supported by the rearfoot, the midfoot and the forefoot in the various test configurations. Factorial design of experiments on different response variables showed that the apparent mass is affected by the posture but not by the type of feet contact surface; conversely, the presence of insoles varies with the apparent mass distribution on the different feet parts., Practitioner Summary: The response of standing subjects to whole-body vibration has always been considered as a global parameter measured at the driving point, neglecting the local phenomena occurring in different foot parts. We have experimentally identified the apparent mass distribution of subjects in different standing postures and with different foot supports.

Phase correction is a critical procedure for most space-borne Fourier transform spectrometers (FTSs) whose accuracy (owing to often poor signal-to-noise ratio, SNR) can be jeopardized from many uncontrollable environmental conditions. This work considers the phase correction in an FTS working under significant temperature change during the measurement and affected by mechanical disturbances. The implemented method is based on the identification of an instrumental phase that is dependent on the interferometer temperature and on the extraction of a linear phase component through a least-squares approach. The use of an instrumental phase parameterized with the interferometer temperature eases the determination of the linear phase that can be extracted using only a narrow spectral region selected to be immune from disturbances. The procedure, in this way, is made robust against phase errors arising from instrumental effects, a key feature to reduce the disturbances through spectra averaging. The method was specifically developed for the Mars IR Mapper spectrometer, that was designed for operation onboard a rover on the Mars surface; the validation was performed using ground and in-flight measurements of the Fourier transform IR spectrometer planetary Fourier spectrometer, onboard the MarsExpress mission. The symmetrization has been exploited also for the spectra calibration, highlighting the issues deriving from the cases of relevant beamsplitter emission. The applicability of this procedure to other instruments is conditional to the presence in the spectra of at least one spectral region with a large SNR along with a negligible (or known) beamsplitter emission. For the PFS instrument, the processing of data with relevant beamsplitter emission has been performed exploiting the absorption carbon dioxide bands present in Martian spectra., (© 2011 Optical Society of America)

We describe the optimization of a mounting system for the infrared (IR) optics of a spaceborne interferometer working in the temperature range between -120 degrees C and +150 degrees C. The concept is based on an aluminum alloy frame with designed mechanical compliance, which allows for compensation of the different coefficient of thermal expansion between the optics and the holder; at the same time, the system provides for the high stiffness required to reach natural frequencies above 200 Hz, which are mandatory in most space missions. Thermal adapters with properly chosen thermomechanical characteristics are interposed between the metallic structure and the lens, so as to reduce the interface stresses on the mechanically weak IR material, due to both the thermoelastic and acceleration loads. With the proposed mount, the competitive requirements of stiffness and stress-free mounting can be matched in wide temperature ranges. The case study of the interferometer of a miniaturized Fourier transform IR spectrometer is presented.

This paper describes the results of a long-term whole-body-vibration monitoring campaign performed on different cars with different drivers. The weighted and the un-weighted root-mean-square acceleration, the MTVV and the VDV have been monitored on five different cars in regular usage for over one hundred hours of measurements on urban roads and highways. The variability of the above parameters has been statistically analyzed in order to assess the time requested for the convergence of standard indexes to their average values. The aim is to supply a general reliability evaluation so as to minimize the on-field tests and to provide a scientific support to the design of such experiments. A comparison between different vehicles is presented and discussed; the correlation with speed measured by a GPS system is analyzed with probabilistic assessments. Results showed that the minimum time for reliable measurement was approximately 30 min for each driving condition (urban, carriage road, highway). The MTVV/a(w) ratio was usually larger than 1.5 (even on short measurement periods), thus indicating the unsuitability of the basic ISO 2631 criterion. The 8-h based VDV provided indications compatible with the a(v) criterion.