Online Spatial and Temporal Calibration for Monocular Direct Visual-Inertial Odometry.

Owing to the nonlinearity in visual-inertial state estimation, sufficiently accurate initial states, especially the spatial and temporal parameters between IMU (Inertial Measurement Unit) and camera, should be provided to avoid divergence. Moreover, these parameters are required to be calibrated online since they are likely to vary once the mechanical configuration slightly changes. Recently, direct approaches have gained popularity for their better performance than feature-based approaches in little-texture or low-illumination environments, taking advantage of tracking pixels directly. Based on these considerations, we perform a direct version of monocular VIO (Visual-inertial Odometry), and propose a novel approach to initialize the spatial-temporal parameters and estimate them with all other variables of interest (IMU pose, point inverse depth, etc.). We highlight that our approach is able to perform robust and accurate initialization and online calibration for the spatial and temporal parameters without utilizing any prior information, and also achieves high-precision estimates even when large temporal offset occurs. The performance of the proposed approach was verified through the public UAV (Unmanned Aerial Vehicle) dataset.

Symmetry of Gait in Underweight, Normal and Overweight Children and Adolescents.

Abnormal excess or lack of body mass can influence gait patterns, but in some cases such differences are subtle and not easy to detect, even with quantitative techniques for movement analysis. In these situations, the study of trunk accelerations may represent an effective way to detecting gait anomalies in terms of symmetry through the calculation of Harmonic Ratio (HR), a parameter obtained by processing trunk accelerations in the frequency domain. In the present study we used this technique to assess the existence of differences in HR during gait in a cohort of 75 healthy children and early adolescents (aged 7-14 years) stratified into 3 equally-sized age and gender-matched groups (Underweight: UW; Normal Weight: NW; Overweight: OW). The accelerometric signal, acquired using a single wearable inertial sensor, was processed to calculate stride length, speed, cadence and HR in antero-posterior, vertical and medio-lateral directions. No differences in spatio-temporal parameters were found among groups, while the HR in the medio-lateral direction was found significantly lower in UW children, while OW exhibited the highest values. On the basis of the results obtained, HR appears capable of discriminating gait symmetry in children with different body mass even when conventional gait parameters are unchanged.

Effects of different percentages of body weight support on spatiotemporal step characteristics during running.

This study aimed to determine the effect of different percentages of body weight support (BWS) on spatiotemporal step characteristics during running. 26 endurance runners (age: 37 ± 9 years) completed a running treadmill protocol consisting of 6 different conditions (BWS combinations: 0-50%), with velocity maintained at 12 km/h. Each condition lasted 1 minute. Step angle, ground contact time (CT), flight time (FT), step length (SL) and frequency (SF), and duration of phases during stance time (phase1: initial contact; phase2: midstance; phase3: propulsion) were measured for every step during the test using a photoelectric cell system. Compared with the baseline condition (100% BW), FT was longer, CT was shorter, SL was longer, SF was lower, and the step angle was higher with each increase in BWS (p < 0.05). Also, some changes were observed in the duration of phases during stance time: phase1 did not experience changes across experimental conditions (p = 0.096), phase2 decreased and phase3 increased as BW was supported (p < 0.05). These results indicate that as BW was supported, runners showed longer FT and SL, shorter CT, lower SF, and greater step angle as well as some changes in the phases during the ground contact. Therefore, this study highlights the effect of different percentages of BWS on spatiotemporal parameters.

Long-term gait analysis in patients after total knee arthroplasty: A systematic review and meta-analysis.

BACKGROUND: Gait abnormalities have been described in patients after total knee arthroplasty (TKA), leading to the development of inter-joint coordination abnormalities and increased risk of falling. Such impairments have been reported to persist in the long-term, although the majority of studies assessed gait pattern especially in the first months after TKA. RESEARCH QUESTION: What are the long-term gait impairments in patients after TKA compared to healthy age-matched subjects? METHODS: A systematic search was conducted on MEDLINE/PubMed, EMBASE, CENTRAL and Scopus databases. Observational studies or randomized controlled trials investigating gait spatial-temporal, kinematic and kinetics parameters in a time-window longer than 6 months in patients with TKA compared to healthy age-matched subjects were included. Methodological quality was assessed using the modified Downs and Black (D&B) checklist and participants' characteristics, surgical procedures details and outcome measures were extracted. Pooled or un-pooled findings were categorized into "6 months - 1 year" and "more than 1 year" timepoint categories. RESULTS: Twenty-eight studies (976 patients) were included. Overall quality was fair with a mean modified D&B score of 63.5 %. Reduced speed, stride length, cadence and longer stance phase were found in patients when compared to healthy individuals at "6 months - 1 year" follow-up. Spatial-temporal parameters deficits were also found at more than 1 year after TKA, where lower single-limb support and longer double-limb support durations were detected. These impairments occurred in concomitance with decreased knee range of motion along the sagittal and frontal planes and altered kinetic parameters. Hip kinematic and kinetic long-term impairments were also detected after TKA. SIGNIFICANCE: These findings highlighted long-term gait pattern alterations in patients with TKA compared to age-matched healthy subjects. Future studies should identify interventions able to reduce long-term gait pattern alterations and improve function in patients after TKA.

Vibrations on mastoid process alter the gait characteristics during walking on different inclines.

Background: Eighty-eight percent of the persons with bilateral vestibular dysfunction have reported at least one fall within the past 5 years. The apparent alternations due to the bilateral vestibular dysfunctions (BVD) are the gait characteristics, such as slower walking speed, prolonged stance phase, and shorter step length. Unexpectedly, due to the prevalence of this BVD being relatively low, attention is not obtained as same as in other vestibular disorders. Moreover, how does walking on different inclines, part of daily activities, alter the gait characteristics under the unreliable bilateral vestibular systems? Previous studies used vibration-based stimulations (VS) as a perturbation to understand the postural control during walking while the bilateral vestibular systems were perturbed. Therefore, this study attempted to extend the knowledge to understand the alternations in spatial-temporal gait characteristics under perturbed bilateral vestibular systems while walking on different inclines. Methods: Nineteen healthy young adults participated in this study. Eight walking conditions were randomly assigned to each participant: 0%, 3%, 6%, and 9% grade of inclines with/without VS. The preferred walking speed was used for gait analysis. The dependent variables were stance time, double support time, step length, step time, step width, foot clearance, and respective variabilities. All dependent variables were defined by two critical gait events: heel-strike and toe-off. Pre-Hoc paired comparisons with Bonferroni corrections were used to prioritize the dependent variables. A two-way repeated measure was used to investigate the effect of VS and the effect of inclines on the selected dependent variables from Pre-Hoc analysis. Post-Hoc comparisons were also corrected by the Bonferroni method. Results: The step length, step time, foot clearance, and foot clearance variability were selected by the Pre-Hoc analysis because the corrected paired t-test demonstrated a significant VS effect (p < 0.05) on these gait parameters at least one of four inclines. The significant interaction between the effect of VS and the effect of inclines was found in step length (p = 0.005), step time (p = 0.028), and foot clearance variability (p = 0.003). The results revealed that implementing a VS increased step length and step time when walking on 0%, 3%, and 9% of grade inclines. In particular, the foot clearance variability was found when walking on 9% of grade inclines. Conclusion: The observations in the current study suggested that VS increased the step length, step time, foot clearance, and foot clearance variability while walking on inclines. These results suggested that these gait parameters might be promising targets for future clinical investigations in patients with BVD while walking on different inclines. Importantly, the increases in spatial-temporal gait performance under bilateral VS might be an indicator of gait improvement while walking on different inclines.

Gait and posture are correlated domains in Parkinson's disease.

Establishing a relationship between gait and posture in patients with Parkinson's disease (PD) is essential for PD treatment and rehabilitation. While previous studies have indicated that gait and posture are independent domains in PD, shared neuromechanisms related to gait and posture control and previous studies investigating the relationship between gait and posture parameters in stroke survivors and neurologically healthy older adults have shown a correlated domain. Thus, this study analyzed the relationship of gait and posture domains, primarily through gait temporal sub-phases (i.e., double support and stance phases) and step width. We analyzed the spatial-temporal gait parameters at the self-selected velocity and center of pressure (CoP) during quiet standing of 22 idiopathic PD participants under and without dopaminergic medication conditions. The association between quiet standing and gait variables was assessed through the Spearman test, controlled by age, disease duration, NFoG-Q, and levodopa dosage. In ON medication, CoP area showed a significant correlation with stance phase and total double support; and RMS ML CoP showed a significant correlation with stance phase, total double support, and step width. In OFF medication, CoP area, RMS AP CoP, RMS ML CoP, and ML CoP velocity significantly correlated with stance phase and total double support. By showing the relationship between gait and posture domains in PD, our study adds novel knowledge about the shared gait-posture control, which could collaborate with new approaches during mobility treatment and assessment.

Smoothness of gait detects early alterations of walking in persons with multiple sclerosis without disability.

In people with Multiple Sclerosis (pwMS) with little or no signs of disability, early detection of walking impairments represents a challenging issue, as simple gait metrics (e.g. speed, cadence, stride length, etc.) may not significantly differ from those of healthy individuals. In this study, we aimed to assess the existence of possible differences in spatial-temporal parameters and smoothness of gait measures (assessed through Harmonic Ratio, HR) obtained from trunk accelerations between 50pwMS without disability (Expanded Disability Status Scale score =1) and 50 age-matched healthy controls. The results show no differences in terms of gait velocity, stride length, stance/swing and double support phases duration, while HR in the direction of motion was significantly lower in pwMS (2.92 vs. 3.67, p<0.001), thus indicating a less smooth gait. The study of trunk accelerations through calculation of HR represents a fast, non-intrusive technique that allows early identification of anomalies in gait patterns of pwMS in absence of disability.

Gait characteristics of children with cerebral palsy as they walk with body weight unloading on a treadmill and over the ground.

Body weight support (BWS) has become a typical strategy for gait training, in special with children with cerebral palsy (CP). Although several findings have been reported in the literature, it remains uncertain how different types of surfaces and gradual amount of BWS can facilitate the mobility of children with CP. The aim of this study was to investigate gait kinematic parameters of children with CP by manipulating BWS and two different types of ground surfaces. Ten children (7.7 ± 2.1 years old) diagnosed with spastic CP and GMFCS classification between levels II and IV were asked to walk on a treadmill and over the ground. In both conditions, BWS was manipulated to minimize gravitational effects and spatial-temporal gait parameters and lower limb joints were analyzed. The results revealed that the type of ground surface causes greater impact on the gait pattern of children with CP as compared to body weight unloading. This finding may provide new insights into the behavioral heterogeneity of children with CP, and offers critical information to be considered on interventional programs specifically designed to improve mobility on this population.

Influence of body weight unloading and support surface during walking of children with cerebral palsy / Influência do alívio de peso corporal e da superfície de suporte durante o andar de crianças com paralisia cerebral espástica

Introduction Partial body weight support (BWS) systems have been employed for gait training of children with cerebral palsy (CP). Therefore, it would be important to analyze if the type of walking surface and the amount of body weight unloading over lower limbs change the way these children walk. Objectives Investigate the influence of walking surface and amount of body weight unloading on the spatial temporal characteristics during walking of children with CP. Materials and methods Seven children with spastic CP between four and eight years old and GMFCS (Gross Motor Function Classification System) between I and IV, were videotaped walking with 0%, 15% and 30% of BWS on both dynamic (treadmill) and static (ground level) surfaces. Walking spatial temporal variables were calculated. Results Children walked with similar velocity in all experimental conditions. While stance duration decreased as the percentage of BWS increased, no differences were found for stance and swing periods and cadence. Children walked with longer steps and strides and with faster strides on static surface compared to dynamic surface. Conclusion Children with CP presenting different levels of motor impairment presented some alterations in the spatial temporal walking parameters as they walked with body unloading. However, such alterations might be due mainly to the type of walking surface than the percentage of body weight unloading on lower limbs.

Introdução Sistemas de suporte parcial de peso corporal (SPPC) têm sido utilizados para treinamento do andar de crianças com paralisia cerebral (PC). Sendo assim, seria importante analisar se o tipo de superfície e a quantidade de alívio de peso corporal sobre os membros inferiores interferem na forma como essas crianças andam. Objetivo Investigar a influência do tipo de superfície e da porcentagem de alívio de peso corporal sobre as características espaço-temporais durante o andar de crianças com PC. Materiais e métodos Sete crianças com PC espástica, entre quatro e oito anos de idade, e GMFCS (Gross Motor Function Classification System) entre I e IV, foram filmadas andando com 0%, 15% e 30% de SPPC em superfícies móvel (esteira motorizada) e fixa (chão). Variáveis espaço-temporais do andar foram calculadas. Resultados As crianças andaram com velocidade semelhante em todas as condições experimentais. Enquanto que a duração do período de apoio diminuiu conforme a porcentagem de SPPC aumentou, nenhuma diferença para as fases de apoio e balanço e cadência foi encontrada. As crianças andaram com passos e passadas mais longos e passadas mais rápidas na superfície fixa do que na superfície móvel. Conclusão Crianças com PC com diferentes níveis de acometimento motor apresentaram algumas alterações nos parâmetros espaço-temporais durante o andar com alívio de peso corporal em superfícies móvel e fixa. Entretanto, tais alterações podem ser atribuídas principalmente ao tipo de superfície em que as crianças andam do que às porcentagens de alívio de peso corporal proporcionadas aos membros inferiores.

Análise do uso de suporte parcial de peso corporal em esteira e em piso fixo durante o andar de crianças com paralisia cerebral / Analysis of partial body weight support during treadmill and overground walking of children with cerebral palsy

OBJETIVO: Analisar características espaço-temporais e ângulos articulares de crianças com paralisia cerebral andando sem o uso de suporte parcial de peso corporal (SPPC) em piso fixo e com 0 por cento e 30 por cento de SPPC em piso fixo e em esteira. MÉTODOS: Seis crianças com paralisia cerebral hemiplégica espástica (7,70±1,04 anos) foram filmadas andando com velocidade confortável sem o uso de SPPC, com 0 por cento e 30 por cento de SPPC em piso fixo e com 0 por cento e 30 por cento de SPPC em esteira. Marcadores refletivos foram afixados nos principais pontos anatômicos dos dois hemicorpos para registro das coordenadas "x", "y", "z". RESULTADOS: As crianças andaram mais rapidamente e com passadas mais longas e mais rápidas, com duração dos períodos de apoio simples e balanço maiores e apoio duplo menor no piso fixo do que na esteira, independentemente do uso do SPPC. O quadril foi a única articulação que apresentou diferenças entre os hemicorpos e entre as condições, sendo que o hemicorpo plégico apresentou menor amplitude de movimento (ADM) que o hemicorpo não plégico, e a ADM foi maior na condição sem o uso de SPPC do que com 30 por cento de SPPC em piso fixo. CONCLUSÃO: Crianças com paralisia cerebral hemiplégica espástica são capazes de andar em piso fixo e esteira com diferentes porcentagens de SPPC, sendo que seus desempenhos foram melhores no piso fixo, independentemente do uso de SPPC, do que na esteira.

OBJECTIVE: To analyze the spatial-temporal characteristics and joint angles during overground walking without body weight support (BWS) and with 0 percent and 30 percent BWS, and during treadmill walking with the same BWS in children with cerebral palsy. METHODS: Six children with hemiplegic and spastic cerebral palsy (7.70 ± 1.04 years old) were videotaped during overground walking at a comfortable speed with no BWS, with 0 percent and 30 percent BWS, and during treadmill walking with 0 percent and 30 percent BWS. Reflective markers were placed over main bony landmarks in both body sides to register the coordinates "x", "y", "z". RESULTS: During overground walking, children walked faster and presented longer and faster strides, longer duration of single-stance and swing periods, and shorter duration of double-stance period, than treadmill walking, regardless of BWS use. The hip was the only joint that presented a difference between body sides and experimental conditions; i.e. range of motion (ROM) was reduced in the plegic side when compared to the nonplegic side, and during overground walking without BWS when compared to 30 percent BWS. CONCLUSION: Children with hemiplegic and spastic cerebral palsy were able to walk overground and on a treadmill with different percentages of BWS, and their performance was superior during overground walking, regardless of BWS use.