Lower limb joint kinetics in the starting blocks and first stance in athletic sprinting

The aim of this study was to examine lower limb joint kinetics during the block and first stance phases in athletic sprinting. Ten male sprinters (100 m PB, 10.50 ± 0.27 s) performed maximal sprint starts from blocks. External force (1000 Hz) and three-dimensional kinematics (250 Hz) were recorded in both the block (utilising instrumented starting blocks) and subsequent first stance phases. Ankle, knee and hip resultant joint moment, power and work were calculated at the rear and front leg during the block phase and during first stance using inverse dynamics. Significantly (P < 0.05) greater peak moment, power and work were evident at the knee joint in the front block and during stance compared with the rear block. Ankle joint kinetic data significantly increased during stance compared with the front and rear block. The hip joint dominated leg extensor energy generation in the block phase (rear leg, 61 ± 10%; front leg, 64 ± 8%) but significantly reduced during stance (32 ± 9%), where the ankle contributed most (42 ± 6%). The current study provides novel insight into sprint start biomechanics and the contribution of the lower limb joints towards leg extensor energy generation.     

Effect of cadence selection on peak power and time of power production in elite BMX riders: A laboratory based study

ABSTRACT

The aims of this study were to analyse the optimal cadence for peak power production and time to peak power in bicycle motocross (BMX) riders. Six male elite BMX riders volunteered for the study. Each rider completed 3 maximal sprints at a cadence of 80, 100, 120 and 140 revs · min^?1 on a laboratory Schoberer Rad Messtechnik (SRM) cycle ergometer in isokinetic mode. The riders’ mean values for peak power and time of power production in all 3 tests were recorded. The BMX riders produced peak power (1105 ± 139 W) at 100 revs · min^?1 with lower peak power produced at 80 revs · min^?1 (1060 ± 69 W, (F(2,15) = 3.162; P = .266; η² = 0.960), 120 revs · min^?1 (1077 ± 141 W, (F(2,15) = 4.348; P = .203; η² = 0.970) and 140 revs · min^?1 (1046 ± 175 W, (F(2,15) = 12.350; P = 0.077; η² = 0.989). The shortest time to power production was attained at 120 revs · min^?1 in 2.5 ± 1.07 s. Whilst a cadence of 80 revs · min^?1 (3.5 ± 0.8 s, (F(2,15) = 2.667; P = .284; η² = 0.800) 100 revs · min^?1 (3.00 ± 1.13 s, (F(2,15) = 24.832; P = .039; η² = 0.974) and 140 revs · min^?1 (3.50 ± 0.88 s, (F(2,15) = 44.167; P = .006; η² = 0.967)) all recorded a longer time to peak power production. The results indicate that the optimal cadence for producing peak power output and reducing the time to peak power output are attained at comparatively low cadences for sprint cycling events. These findings could potentially inform strength and conditioning training to maximise dynamic force production and enable coaches to select optimal gear ratios.     

Measuring the cultural value of the Royal Scottish Academy New Contemporaries Exhibition as a platform for emerging artists

In our analysis of the cultural value of the Royal Scottish Academy New Contemporaries Exhibition, we assessed the institution's role in shaping emerging artists’ careers, as well as wider cultural value. Supported by our conceptual framework of value creation, issues assessed included the expected versus experienced value of the exhibition and the individual artworks, price setting, the market mechanism surrounding the exhibition, and its enhancement. The created cultural value is facilitated by high-visibility media exposure and through development of career-enhancing networks. We have generated new insight into cultural value more generally by moving beyond dominant instrumental valuation approaches. We have addressed many of the gaps in understanding the mechanisms behind engagement with contemporary art. We have progressed theory with the assistance of our conceptual framework and supporting qualitative data. Cultural value is expressed in contemporary art through artistic production systems and its cultural messages. Artists’ cultural value is often constructed via the intrinsic worth of their work, rather than from market influences. Cultural value is often personal to the viewer, shared with others and remembered over time. It is also co-created among the other stakeholders involved.     

Object‐Oriented Performance Improvement

In this paper, a framework to support an object‐oriented approach to performance analysis is described. The framework includes the use of collaboration, automation, visual modeling, and reusable repositories of analysis knowledge. The need for a new framework is related to the increasing concern with the cost effectiveness of student and employee development. Efforts to improve the return‐on‐investment in such development have been hindered by a craft orientation to the design and construction of learning and performance support materials. One solution to this problem has been to enhance the reuse of such materials. Rather than build every new system from scratch in a craft‐oriented manner, it is envisioned that systems will be constructed largely of standardized, reusable objects shared through Web‐based repositories. Currently, the main focus is on the technological framework necessary for an object‐based approach to learning system development. There appears to be little consideration of the changes in analysis and design thinking required for the move towards object‐based systems. Such systems should still be required to be directly linked to performance problems and opportunities at both the organizational and individual system levels.     

高水平教练员获取科研成果的途径

为保持优秀运动员的运动优势,高水平教练员必须不断提高自身的知识水平和结构.但体育科研在运动成绩中所占的比重及科研成果向教练员传递的有效机制,我们还了解甚少.     

Child extrafamilial sexual abuse: predicting parent and child functioning

Objective: This study evaluated the emotional and behavioral adjustment of parents and children within 3 months and 1 year after the discovery of child extrafamilial sexual abuse.Method: Ninety-two case parents (63 mothers, 29 fathers) and 56 children were compared to a nonclinical comparison group of 136 parents (74 mothers, 62 fathers) and 75 children. Parent adjustment was assessed using self-report measures while child functioning was assessed using a combination of child-, parent- and teacher-report measures.Results: Mothers, fathers and sexually abused children experienced clinically significant effects both initially and at 12 months post-disclosure. Children’s perceptions of self-blame and guilt for the abuse and the extent of traumatization predicted their self-reported symtomatology at 3 months and 1 year post-disclosure. Child age and gender also significantly contributed to the prediction of many of the child outcome measures. No abuse-related variable was related to any child self-report measure. Mothers’ satisfaction in the parenting role, perceived support and intrusive symptoms predicted their initial emotional functioning. Avoidant symptoms, child’s internalizing behavior and mothers’ initial emotional functioning were significant predictors of longer-term emotional functioning.Conclusions: Results emphasize the need to address children’s abuse-related attributions and underscore the need to expand our focus beyond the child victims to the traumatized families.     

Radical Constructivism. Ernst von Glasersfeld.

Radical Constructivism is currently a very influencial view in mathematics education. This paper examines its philosophical roots through a review of the book Radical Constructivism by Ernst von Glasersfeld. It begins by describing the structure of the book, and then considers a number of philosophical issues raised by the book. The paper concludes with some reflections on the relationship between philosophy and mathematics education which the book provoked.     

Time-optimal Control Systems with Norm Constraints on State Variables at Intermediate Times

The problem of time-optimal control systems with both norm constraints on control inputs and on state variables at discrete intermediate times is formulated as an L-problem in the theory of moments. The simplex method is used for solving a nonlinear minimizing problem inherent in the functional analysis solution to this latter problem. Numerical results are presented for a train operation.