Model-based automatic tracking of articulated human movement

This study applied a vision-based tracking approach to the analysis of articulated, three-dimensional (3D) whole-body human movements. A 3D computer graphics model of the human body was constructed from ellipsoid solids and customized to two gymnasts for size and colour. The model was used in the generation of model images from multiple camera views with simulated environments based on measurements taken on each of three synchronized video cameras and the lighting sources present in the original recording environment. A hierarchical procedure was used whereby the torso was tracked initially to establish whole-body position and orientation and subsequently body segments were added successively to the model to establish body configuration. An iterative procedure was used at each stage to optimize each new set of variables using a score based on the RGB colour difference between the model images and video images at each stage. Tracking experiments were carried out on movement sequences using both synthetic and video image data. Promising qualitative results were obtained with consistent model matching in all sequences, including sequences involving whole-body rotational movements. Accurate tracking results were obtained for the synthetic image sequences. Automatic tracking results for the video images were also compared with kinematic estimates obtained via manual digitization and favourable comparisons were obtained. It is concluded that with further development this model-based approach using colour matching should provide the basis of a robust and accurate tracking system applicable to data collection for biomechanics studies.     

规律运动与性别差异对高中生身体意象的影响

选用多维度身体与自我关系问卷作工具,对浙江省4所高级中学进行调查.结果显示:(1)除外表取向和疾病取向外,性别差异对高中生的身体意象其他各维度都具有显著影响.男生的外表评价、体能评价、健康评价、身体各部位满意度、体能关注、健康关注显著高于女生.(2)除对头发的满意度无显著性别差异外,对其他身体部位的满意度,男生显著高于女生.(3)规律运动对外表评价、体能评价、健康评价和体能取向有显著影响,而对其他身体意向构成维度没有显著影响.     

Reliability and agreement between DXA-derived body volumes and their usage in 4-compartment body composition models produced from DXA and BIA values

Two research groups recently produced equations for estimation of body volume from dual-energy x-ray absorptiometry (DXA) scans. These body volume estimates can be used for body composition evaluation in modified 4-compartment models. In the present analysis, the reliability of body volume calculations, as well as their usage in 4-compartment models, was explored while employing precise scheduling of assessments and dietary standardization. Forty-eight recreationally active males and females completed two pairs of identical assessments, which included a DXA scan and single-frequency bioelectrical impedance analysis. Each assessment within a pair was separated by 24 hours, during which participants were provided a standardized diet. Body volume and 4-compartment equations were applied to the data, and metrics of reliability and agreement were calculated for body volume and 4-compartment components. While both body volume equations demonstrated excellent reliability individually, substantial disagreement between equations was present when utilized in 4-compartment equations. The magnitude of this disagreement was 4.3 kg for lean mass and fat mass and 6.9% for body fat percentage. At present, the large discrepancies in body composition components when using existing body volume equations preclude their interchangeability and demonstrate the need for continued exploration of the utility of body volume estimates.     

Associations between anxiety,self-efficacy,and outcomes by gender and body size dissatisfaction during fitness in high school physical education

Background: Noteworthy proportions of adolescents – particularly females – report negatively about their experiences regarding fitness and the testing of it during physical education (PE). These accounts often coincide with lower levels of body image, fitness, motivation, and physical activity and higher rates of attrition from optional PE.

Purpose: The aim of this study was to test path relations between body size dissatisfaction (BSD), test anxiety (TA), self-efficacy, and fitness-related outcomes during fitness in PE and to determine whether these differ as a function of gender and level of BSD.

Method: Survey data were collected from 394 9th and 10th-grade students in southern Ontario, Canada. A previously validated BSD measure was used that consisted of a series of nine gender-specific silhouettes ranging from very thin/slender to very large/overweight. Students’ dissatisfaction score involved subtracting self-ratings of their ideal body size from current body size estimates. Fitness indices in PE (FIPE)was the z-score of the sum of self-reported fitness level, fitness grade in PE, and frequency of active exercise at least 30 minutes per day. Self-efficacy and TA were assessed using established scales from the Motivated Strategies for Learning Questionnaire.

Data analysis: Multivariate analysis of variance was used to assess group differences whereas gender-specific confirmatory factor and path analyses were used to test the proposed path in which relations between BSD and FIPE were manifest indirectly through TA and self-efficacy.

Findings: The hypothetical path fit the data in the overall sample and fit better for females than for males. Females reported a higher BSD and a lower self-efficacy and FIPE than males. BSD was evident in both genders with most females desiring a thinner body compared to boys who had relatively equal proportions wanting to be bigger and thinner. Males wanting to be smaller reported significantly lower self-efficacy and FIPE than males with little BSD or those wanting to be larger. Females desiring a thinner body reported significantly more TA and lower FIPE than females with no BSD.

Conclusion: Body image concerns and elevated levels of anxiety appear to undergird the influence of self-efficacy on FIPE. This is particularly so in females, although both females and males with a BSD are susceptible to lowered fitness motivation and achievement in PE. Suggestions are provided to help physical educators to structure fitness curricula and pedagogy to better minimize this vulnerability. These include catering to the gender-specific needs and preferences for fitness activities during PE including the testing of fitness.