Biomechanical determinants of cross-country skiing performance: A systematic review

ABSTRACT

Cross-country skiing is a complex endurance sport requiring technical skills, in addition to considerable physiological and tactical abilities. This review aims to identify biomechanical factors that influence the performance of cross-country skiers. Four electronic databases were searched systematically for original articles in peer-reviewed journals addressing the relationship between biomechanical factors (including kinematics, kinetics, and muscle activation) and performance while skiing on snow or roller skiing. Of the 46 articles included, 22 focused exclusively on the classical technique, 18 on the skating technique, and six on both. The indicators of performance were: results from actual or simulated races (9 articles); speed on specific tracts (6 articles); maximal or peak speed (11 articles); skiing economy or efficiency (11 articles); and grouping on the basis of performance or level of skill (12 articles). The main findings were that i) cycle length, most often considered as a major determinant of skiing speed, is also related to skiing economy and level of performance; ii) higher cycle rate related with maximal speed capacity, while self-selected cycle rate improves skiing economy at sub-maximal speeds; iii) cross-country skiing performance appears to be improved by joint, whole-body, ski, and pole kinematics that promote forward propulsion while minimizing unnecessary movement.     

Selective spatial working memory impairment in a group of children with mathematics learning disabilities and poor problem-solving skills

This study examines visual and spatial working memory skills in 35 third to fifth graders with both mathematics learning disabilities (MLD) and poor problem-solving skills and 35 of their peers with typical development (TD) on tasks involving both low and high attentional control. Results revealed that children with MLD, relative to TD children, failed spatial working memory tasks that had either low or high attentional demands but did not fail the visual tasks. In addition, children with MLD made more intrusion errors in the spatial working memory tasks requiring high attentional control than did their TD peers. Finally, as a post hoc analysis the sample of MLD was divided in two: children with severe MLD and children with low mathematical achievement. Results showed that only children with severe MLD failed in spatial working memory (WM) tasks if compared with children with low mathematical achievement and TD. The findings are discussed on the basis of their theoretical and clinical implications, in particular considering that children with MLD can benefit from spatial WM processes to solve arithmetic word problems, which involves the ability to both maintain and manipulate relevant information.     

Influence of motivational beliefs and strategies on recall task performance in elementary, middle and high school students

In the present study, we propose a model describing how motivational beliefs and strategies influence study performance of students at three different school levels: elementary (age 8-10), middle (11-14), and first year high school (15). Participants were administered the AMOS 8-15 instrument (Cornoldi et al. 2005) designed for measuring the influence of motivational beliefs and strategies on recall task performance. Results of multigroup analysis confirmed the relations proposed in our model between motivational beliefs and strategies for all three groups, the largest difference being in how these aspects influenced performance on recall tasks: in elementary and middle school, motivational beliefs have direct influence on performance, whereas in high school they influence performance through strategy use.     

Preschoolers' Communicative Functions During Shared Book Reading With Mothers and Fathers

Research Findings: This study examined whether the communicative behaviors of preschoolers during shared-reading interactions differ according to child age or parent gender. Twenty Italian preschoolers (from 3.1 to 5.11 years) were observed during book reading with each parent separately. Communicative behaviors were analyzed according to the speech act theory. The findings showed that older children produced significantly more requests with fathers than with mothers but significantly more assertions with mothers than with fathers. Sequential analysis showed that only the fathers' reading utterances were significantly followed by older children's requests. These results suggest that older children adjusted their communicative functions to elicit richer conversations from their fathers. Practice or Policy: These findings have implications for the assessment and support of preschoolers' conversational skills.     

Supporting preschoolers’ cognitive development: Short- and mid-term effects of fluid reasoning,visuospatial, and motor training

Cognitive abilities are essential to children's overall growth; thus, the implementation of early and effective training interventions is a major challenge for developmental psychologists and teachers. This study explores whether an intervention simultaneously operating on fluid reasoning (FR), visuospatial, narrative, and motor abilities could boost these competencies in a group of Italian preschoolers (N = 108, 54 males 54 females, Age_mean = 4.04). FR and visuospatial abilities showed training-related increases at the end of the training and 1-year follow-up (moderate effect size). Interestingly, positive correlations with working memory and mathematical abilities were found. Beyond their scientific relevance, the short- and long-term effects provide fundamental indications for designing and implementing educational programs dedicated to preschoolers.     

Dynamic assessment and teachers' knowledge of children's mathematical thinking: a case study in children's mathematics

This paper considers the kind of pedagogical knowledge and principles involved in the operationalisation of knowledge of children's mathematical thinking as a process of dynamic assessment. Using a case study of a particular child, this paper explores planning and instruction for a child determined by a detailed and informed interpretation of the child's conceptual understanding through a dynamic process. It presents as a case study the observations of a teacher who had undertaken professional development in children's mathematical thinking, theoretically informed by Cognitively Guided Instruction and Maths Recovery. The observations revealed the child's mathematical understanding and how the teacher used this knowledge dynamically to inform teaching. The paper outlines the kind of knowledge required of teachers to enact this dynamic process in mathematics teaching and argues for the centrality of this to the development of inclusive practice.     

The role of working memory in spatial text processing: What benefit of imagery strategy and visuospatial abilities?

This study investigated the construction of a spatial model in relation to working memory (WM) and visuospatial abilities. Participants were trained to use either imagery or verbal strategies to process route spatial texts. Results obtained on a free recall task, a verification test and a graphic representation task showed the beneficial effect of using a strategy based on mental images. When imagery strategies were used, a concurrent articulatory task produced interference effects on recall performance, and a spatial tapping task also impaired performance as compared to the control condition. These interference effects suggest that both visuospatial and verbal WM were involved in construction of the spatial model. When repetition strategies were used, however, only the articulatory task produced interference effects, highlighting the role of the verbal WM. To elucidate how the involvement of the visuospatial component may differ in relation to visuospatial abilities, participants with good or poor ability in generation of visual images and spatial manipulation of objects were compared. The benefit of the imagery strategy was found in both groups, but whereas low-visuospatial imagery participants were sensitive to spatial interference, their high ability counterparts were not. These results question the role of imagery processes in the construction of spatial models and their relation to the visuospatial WM.     

Microfluidic generation of PEG-b-PLA polymersomes containing alginate-based core hydrogel

Herein, we demonstrate a novel method for the generation of monodisperse cell-like structures containing a biocompatible hydrogel matrix surrounded by a membrane responsive to chemical cues. Specifically, we employ droplet-based microfluidics to generate PEG-PLA polymersomes encapsulating alginate in liquid form. We investigate alginate core gelation by creating an osmotic pressure gradient across the polymeric membrane that, through expansion, allows the passage of calcium ions. The effects of calcium concentration on the core gelation are explored.