Which starting style is faster in sprint running--standing or crouch start?

The purpose of this study was to further understand the biomechanical differences between the standing and crouch starting methods, and to investigate whether one of the starting styles provides better acceleration and proves to be faster. Six university track team sprinters performed 2 x 3 x 50 m trials. Digitised video, photocell timing, and velocity data revealed that during the first steps of the performance the standing start produced higher body centre of mass horizontal velocity than the crouch start. This may be due to the longer distance between the feet in the standing start, which caused longer push-off phases, and the work against gravity in the crouch start. However, this advantage in horizontal velocity disappeared by the 10 m mark, where similar velocities were recorded with both start styles. Further, there was no statistically significant difference between the two starting styles in horizontal velocity at the 25 m mark, nor in the time to reach the 25 m or 50 m mark. Regarding relay running, where athletes need to decide to adopt either a crouch start without starting blocks or a standing start, there seems to be no specific reason for outgoing athletes to use a crouch start, although this area warrants further investigation.     

Lower limb joint kinetics during the first stance phase in athletics sprinting: three elite athlete case studies

Abstract

This study analysed the first stance phase joint kinetics of three elite sprinters to improve the understanding of technique and investigate how individual differences in technique could influence the resulting levels of performance. Force (1000 Hz) and video (200 Hz) data were collected and resultant moments, power and work at the stance leg metatarsal-phalangeal (MTP), ankle, knee and hip joints were calculated. The MTP and ankle joints both exhibited resultant plantarflexor moments throughout stance. Whilst the ankle joint generated up to four times more energy than it absorbed, the MTP joint was primarily an energy absorber. Knee extensor resultant moments and power were produced throughout the majority of stance, and the best-performing sprinter generated double and four times the amount of knee joint energy compared to the other two sprinters. The hip joint extended throughout stance. Positive hip extensor energy was generated during early stance before energy was absorbed at the hip as the resultant moment became flexor-dominant towards toe-off. The generation of energy at the ankle appears to be of greater importance than in later phases of a sprint, whilst knee joint energy generation may be vital for early acceleration and is potentially facilitated by favourable kinematics at touchdown.     

A simple mechanical model for simulating cross-country skiing,skating technique

The role of simulation models in sport disciplines has become relevant lately due to the multiple advantages that they may offer sports teams, coaches and practitioners. This paper develops and presents a simple three-dimensional multibody dynamic model of a cross-country skier, modeling a single propulsion phase to obtain the kinetic parameters involved in the movement. A professional Olympic-level skier performed the skating technique without poles in a ski tunnel under controlled conditions and on an incline plane. Then, with a force acquisition system attached to the ski bindings and a motion capture system set on site, the leg resultant forces and the movement of specific points of the skier’s lower body were acquired. The data obtained from the motion capture system were used as the prescribed kinematic input data in the multibody model and the measured force was used later as a parameter of comparison with the results of the simple model. After simulating the technique, the calculated resultant forces seem to be in agreement with those measured in the field.     

Changes in technique within a sprint hurdle run

The aim of this study was to understand changes in technique within an athlete's own performance during a sprint hurdles run. Four athletes performed a training session containing four trials each over 10 hurdles. Clearances at hurdles three and nine were videotaped from a side view and manually digitised. All athletes in this study yielded a lower running speed over the hurdle at the ninth hurdle in comparison to the third hurdle in each run. All athletes also showed further signs of potential tiredness in the clearances of the ninth hurdle. Interestingly, these changes in technique varied among the athletes. This poses challenges to coaches, as they need to evaluate individually what changes in training should be introduced to keep the quality of clearances as high as possible throughout training. To match more closely the velocities to those in competitions, consideration could be given in training to shorten gradually the distances between the hurdles more during the latter part of the run, although this should be individually checked, based on the athlete. This way, athletes could learn to clear the hurdle with a higher horizontal velocity, even when fatigue is potentially influencing the performance.     

Choice of sprint start performance measure affects the performance-based ranking within a group of sprinters: which is the most appropriate measure?

Sprint start performance has previously been quantified using several different measures. This study aimed to identify whether different measures could influence the performance-based ranking within a group of 12 sprinters, and if so, to identify the most appropriate measure. None of the 10 performance measures ranked all sprinters in the same order; Spearman's rho correlations between different block phase measures ranged from 0.50 to 0.94, and between block phase measures and those obtained beyond block exit from 0.66 to 0.85. Based on the consideration of what each measure quantifies, normalised average horizontal external power was identified as the most appropriate, incorporating both block velocity and the time spent producing this velocity. The accuracy with which these data could be obtained in an externally valid field setting was assessed against force platform criterion data. For an athlete producing 678 +/- 40 W of block power, a carefully set-up manual high-speed video analysis protocol produced systematic and random errors of +5 Wand +/- 24 W, respectively. Since the choice of performance measure could affect the conclusions drawn from a technique analysis, for example the success of an intervention, it is proposed that external power is used to quantify start performance.     

Using Lesson Study in teacher professional development for domain-based moral education

This study examined the application of Lesson Study for professional development (PD) for a domain approach to moral education. A comparison was drawn between the effects of Lesson Study with 17 teachers and 144 students representing middle schools in the same district as a prior study employing intensive traditional PD. In Lesson Study, groups of same grade teachers construct lessons taught by one group member and observed by the others. Teachers meet following the lesson to critique and improve the lesson using criteria established by teachers and informed by outside ‘experts.’ Findings from analysis of teacher discourse over nine months and end of year surveys revealed improvements in teacher pedagogy, knowledge of moral development, greater sense of professionalism, and efficacy for engagement in moral education in comparison with controls. Fewer lessons were produced, resulting in fewer gains in student moral and conventional reasoning than observed with intensive individualized PD.     

Observations of teacher-child interactions in classrooms serving Latinos and dual language learners: Applicability of the Classroom Assessment Scoring System in diverse settings

With the rising number of Latino and dual language learner (DLL) children attending pre-k and the importance of assessing the quality of their experiences in those settings, this study examined the extent to which a commonly used assessment of teacher-child interactions, the Classroom Assessment Scoring System (CLASS), demonstrated similar psychometric properties in classrooms serving ethnically and linguistically diverse children as it does in other classrooms. Specifically, this study investigated: (1) whether CLASS observations of teacher-child interactions are organized in three domains across classrooms with varying ethnic and language compositions (measurement invariance) and (2) the extent to which CLASS-assessed teacher-child interactions (emotional support, classroom organization, and instructional support) predict children's social, math, and literacy outcomes equally well for Latino and DLL children (predictive validity). CLASS observations of teacher-child interactions were conducted in 721 state-funded pre-k classrooms across 11 states. Direct assessments and teacher ratings of social, math, and literacy outcomes were collected for four randomly selected children in each classroom. CLASS observations factored similarly across pre-k classrooms with different Latino and DLL compositions and predicted improvements in school readiness regardless of a child's Latino or DLL status. Results suggest CLASS functions equally well as an assessment of the quality of teacher-child interactions in pre-k settings regardless of the proportion of Latino children and/or the language diversity of the children in that setting.     

Understanding the effect of touchdown distance and ankle joint kinematics on sprint acceleration performance through computer simulation

This study determined the effects of simulated technique manipulations on early acceleration performance. A planar seven-segment angle-driven model was developed and quantitatively evaluated based on the agreement of its output to empirical data from an international-level male sprinter (100 m personal best = 10.28 s). The model was then applied to independently assess the effects of manipulating touchdown distance (horizontal distance between the foot and centre of mass) and range of ankle joint dorsiflexion during early stance on horizontal external power production during stance. The model matched the empirical data with a mean difference of 5.2%. When the foot was placed progressively further forward at touchdown, horizontal power production continually reduced. When the foot was placed further back, power production initially increased (a peak increase of 0.7% occurred at 0.02 m further back) but decreased as the foot continued to touchdown further back. When the range of dorsiflexion during early stance was reduced, exponential increases in performance were observed. Increasing negative touchdown distance directs the ground reaction force more horizontally; however, a limit to the associated performance benefit exists. Reducing dorsiflexion, which required achievable increases in the peak ankle plantar flexor moment, appears potentially beneficial for improving early acceleration performance.     

Diversity and High Academic Expectations Without Tracking: Inclusively Responsive Instruction

This article presents an instructional model (inclusively responsive instruction) that takes advantage of student diversity in order to differentiate student learning while maintaining high expectations. In the history of U.S. education, diversity and academic rigor were often considered at odds, and educators tried to emphasize one at the expense of the other. This article uses a detailed set of examples from Japanese mathematics education to illustrate how diverse ideas, as important resources, can drive classroom instruction. Teaching and learning supports are described that are essential to helping all teachers balance group and individual learning in classrooms. Current U.S. instructional approaches and the model of inclusively responsive instruction are compared in terms of balancing diversity and academic expectations.     

Parents’ assessments of their children’s abilities

Conducted in the framework of the theory of social representations, the study was designed to examine the dimensions in terms of which parents assess their children’s abilities, the ways in which social positions — here, the parents’ education and gender and the child’s gender — organize these assessments, and the ways in which the assessments relate to the estimated school success of the child. The subjects were a nationwide sample of parents (N=938), who were asked to estimate their children’s school success and to assess these children’s abilities. A factor analysis showed the ability assessments to be multidimensional. The parents assessed girls’ cognitive and social abilities to be better than boys’. Academically educated parents drew a more categorical distinction than other parents between cognitive and other abilities, which suggests that they endorse a differential conception of intelligence. A clear congruity of content was observed between the estimations of school success and the assessments of abilities, indicating that different school subjects are associated with different abilities.