The one- and two-handed backhands in tennis

The study investigated differences in the one- (SH) and two-handed (DH) backhands when hit flat, across-court (AC) and down-the-line (DL), and with heavy topspin DL (TDL). The ability to disguise each of these backhands when hitting the above strokes was also assessed. Eighteen college-level male tennis players, identified as having a high performance topspin SH (n = 6) or DH (n = 12) backhand drive, participated in the study. Players were required to hit three AC, DL and TDL backhands from the baseline with their preferred technique, while being filmed with two high-speed video cameras operating at 200 Hz. The highest horizontal velocity backhand for each stroke was analysed. Results indicated that the sequential coordination of five body segments (hips, shoulder, upper arm, forearm, and hand/racquet rotations) was required for the execution of the SH stroke. The same number of segments were generally coordinated in the DH stroke (hips, shoulders, and varying degrees of upper arm and forearm rotations followed by hand/racquet movement). Mature players produced comparable racquet horizontal velocities 0.005 s prior to impact using either the SH or DH backhand technique. The SH backhand was characterised by a more rotated shoulder alignment than the DH stroke (SH: 119.1 degrees; DH: 83.4 degrees) at the completion of the backswing. At impact the ball was impacted further in front (SH: 0.59 m: DH: 0.40 m) and a similar distance to the side of the body (SH: 0.75 m: DH: 0.70 m). Players using the DH backhand technique delayed the horizontal acceleration of the racquet towards the ball (SH: 0.13 s: DH: 0.08 s prior to impact) and thus were capable of displaying a similar hitting motion closer to impact than players with a SH technique.     

Challenge 98: sustaining the work of a regional technology integration initiative

In this article, we offer a research‐based theoretical framework for sustainability, describing the proven qualities of a project and the innovations that support its sustained existence over time. We then describe how a US Department of Education Technology Innovation Challenge grantee, working to promote technology integration in a socio‐economically disadvantaged region of the state of Texas, succeeded in creating a sustainable set of activities around its work to support educators’ uses of technology. We examine the factors that served to nurture and facilitate sustainability of the practices associated with technology integration to promote student achievement. We take the fact that it is not the project but rather the change in practice that is important.     

Dimensions of teachers’ attitudes toward instructional television

Summary Responses were obtained from 50 fourth and ninth grade teachers on a 55-item test of their attitudes toward television in the classroom after 33 of them had been involved and 17 not involved in television series which introduced new ways of teaching mathematics. Intercorrelations were computed, and factors were analyzed. The resulting factor structure indicated 10 unique factors of the attitudes expressed. No general factor was found. The ten factors were tentatively identified as follows: challenge-threat, economy, instructional side-benefits, partnership between TV and classroom teachers, responsiveness, parental influences, security of the classroom teacher, invidious comparison, experimental attitude, and in-service training. On the whole the teachers’ attitudes were highly favorable to instructional television, and consistently rejected the idea that the TV teacher represents a threat to the classroom teacher.     

Role of joint torques generated in an optimised Yurchenko layout vault

The purpose of the study was to quantify the muscle torques required in the performance of an optimised Yurchenko layout vault based on a five-segment rigid link model and using input data from an elite female gymnast. At impact, the wrist torque trajectory indicated an extension-flexion action while the shoulder was characterised by extension. The approximate 100 Nm (wrist flexor) and 125 Nm (shoulder extensor) respective peak torque magnitudes indicated that the impact action is not passive in nature. The contribution of joint torques to the adjoining segments was apportioned to the relative components namely; centripetal, gravity and net joint torque components. Despite the presence of both large wrist and shoulder joint torques, the net turning effect on the upper limb and hand segments about their centre of mass (CM) was small. The principal role of the upper limb joint torques was therefore to effect the appropriate joint motions and to support the weight of the gymnast. The performance of the optimum vault was primarily the result of the interplay between the centripetal and the net joint torque components at the wrist, hip and shoulder joints. This has implications to the performer in that successful execution of the vault is principally concerned with the ability to create a high angular momentum for horse impact and to then apply an appropriate level of joint torques that will make optimal use of the initial kinetic condition.