不同水平网球选手正手击球技术运动学研究

摘要：在网球的基本技术中,正手被视为发球后最重要的一项技术,本研究主要运用文献资料、测量等研究方法针对国内12名男子网球选手正手击球技术的特征展开研究,重点了解与击球技术动作相关的关节角度,线速度和角速度等运动学特征,旨在揭示不同水平选手技术动作的差异,并进一步认识影响正手击球速度的核心要素。结果表明与一般水平选手相比,优秀选手在正手击球瞬间表现出更快的拍头水平速度和更快的肩部水平速度,但在躯干转动的角速度上却不存在显著性差异。在不考虑组别的情况下,击球时过程中选手的肩、髋、球拍的转动角差异很大,说明考虑标准化的技术动作并没有实际意义。     

“Did you do your homework?” Mathematics teachers’ homework follow‐up practices at middle school level

Teachers’ homework follow‐up practices, the in‐class strategies teachers use to monitor their students’ homework assignments, have an impact on their students’ homework behaviors and academic achievement. The current study explored the perspectives of middle school mathematics teachers on the three domains of homework follow‐up: the practices used in class, the purposes of each practice, and the aspects that may influence this process. Data were collected from two data sources (i.e., focus groups and classroom observations) and were analyzed using thematic analysis. The findings showed that teachers monitored homework either using a single strategy or a combination of strategies (e.g., checking homework completion and providing individual feedback) linked to a specific purpose (e.g., promote students’ involvement). The teachers also reported that they were under certain constraints when they delivered homework follow‐up practices (e.g., pressure to follow the curriculum), so their practices’ effectiveness sometimes can be compromised. Implications for practice are discussed.