How does the tennis serve technique influence the serve-and-volley?

In tennis, a high ball velocity and a fast run toward the net are key features to successful performance of "serve-and-volley" players. For the serve, tennis players can use two techniques: the foot-up (FU) or foot-back (FB) technique. The aim of this study was to determine if the running time toward the net after the serve and the ball velocity (V(ball)) vary between these two techniques. Moreover we analysed the angular momentum values of the trunk and of the arm holding the racquet. Fifteen expert tennis players performed six successful serve-and-volleys with both techniques. Running time to the net is significantly lower for FB, whereas V(ball) is significantly higher for FU. Trunk and arm angular momentums about the transverse axis are significantly higher with FU before ball impact. A significant correlation (r = 0.81, P < 0.001) exists between changes in the maximal trunk angular momentum and in running time to the net between the two serve techniques. A significant correlation (r = 0.84, P < 0.001) also exists between changes in the maximal trunk angular momentum and in V(ball) between the two serve techniques. According to these results, FB is the best technique for moving as quickly as possible to the net because of a lower trunk angular momentum.     

Examining pre-service teachers’ acceptance of technology-rich learning environments: A UAE case study

This study addressed the extent to which pre-service teachers at a teachers’ college in the United Arab Emirates (UAE) accepted and intended to utilize technology-rich learning environments in their future teaching practice. The effect of other significant factors on their overall acceptance, such as computer self-efficacy (CSE) and Perceived User Resources, was investigated. A final aim was to confirm the applicability of the instruments employed in this study within the unique sociocultural context of the UAE. Questionnaires utilizing a modified version of the technology acceptance model (TAM) were used to collect data. Respondents indicated strong acceptance of technology-rich learning environments. In the model, Perceived Usefulness and CSE were the two strongest predictors of Behavioral Intention. The results also supported the validity of TAM-based research within the Emirati sociocultural environment.     

Spontaneous change from seated to standing cycling position with increasing power is associated with a minimization of cost functions

Spontaneous changes of movement patterns may allow to elucidate which criteria influence movement pattern preferences. However, the factors explaining the sit-stand transition in cycling are unclear. This study investigated if biomechanical and/or muscle activation cost functions could predict the power at which the spontaneous sit-stand transition occurs. Twenty-five participants performed an incremental test leading to the sit-to-stand transition, and subsequent randomized pedaling trials at 20 to 120% of the transition power in seated and standing position. A Moment Cost Function based on lower limbs net joint moments and two Electromyographic Cost Functions based on EMG data were defined. All cost functions increased with increasing crank power (p < 0.001) but at different rates in the seated and standing positions. They had lower values in the seated position below the transition power and lower values in the standing position above the transition power (p < 0.05). These results suggest that spontaneous change of position observed in cycling with increasing crank power represents an optimal choice to minimize muscular efforts. These results support the use of simple cost functions to define optimal settings in cycling and to assess the cost of cycling during short-term efforts.     

The promise and peril of the state in neoliberal times: implications for the critical environmental education movement in Brazil

Neoliberal ideology has made an impact on environmental education (EE) policies and practices in Brazil. The EE in Family Agriculture Program, of national scope and administered by the Ministry of the Environment, seeks to promote sustainable development in rural areas, specifically through strategies focused on adult education and non-formal education aimed at small producers (family agriculture). This program reveals profound ideological contradictions between the critical and transformative rhetoric of public policy and the actual program structures and practices administered by the state in a dependent economy, which primarily serve to reinforce a capitalist mode of production marked by high environmental impact and deeply stratified class relations. In the neoliberal era, states intending to protect the environment through critical EE strategies suffer serious limitations due to their role as stewards of a globalized economy based on the supply of raw materials, high-impact land-use, and a cheap labor force.     

Does research organization influence academic production?: Laboratory level evidence from a large European university

The paper analyses scientific research production at the laboratory level. The evidence on which the study is based describes precisely the research activity over the period 1993-2000 of more than eighty labs belonging to Louis Pasteur University, a large and well-ranked European research university. The research organization of the labs is analysed by focusing on the characteristics of the research personnel in relation with the scores in two outcomes that are publications and patents. The paper proposes a five-classes typology of laboratories that highlights different styles of research organization and productivity at the laboratory level. It also studies the determinants of the publication performances of labs. We show how appropriate combinations of inputs in academic labs may be strongly associated to high publication performances. We find that combining full-time researchers and university professors in labs tend to preserve incentives. Highly publishing labs also patent. The size of the labs, the individual promotions, and the role of non-permanent researchers and of non-researchers are also underlined.     

The advantage of distributed practice in a blended learning setting

Education and Information Technologies - Ongoing digital transformations facilitate the conduct of online courses and distance learning. In this study, it was aimed to investigate the role of...     

Mechanics of standing and crouching sprint starts

The aim of this study was to compare the kinetic and kinematic parameters of standing and crouch sprint starts. Parallel starts (PS), false starts (FS), jump starts (JS) and crouch starts (3PS) were compared. Eighteen participants performed each start on a force plate and six infrared cameras captured the three-dimensional coordinates of 36 retro-reflective markers. Performance during a five-metre sprint (T_5m) was analysed. Duration of the start phase (T_start), mean values of horizontal and total ground reaction forces (GRFs) (F_{x_mean} and F_{tot_mean}), ratio of force (RF), maximal power (P_max) and kinetic energy (KE) of each limb were calculated. Significant differences were found for T_5m, T_start, KE, P_max, F_{x_mean}, F_{tot_mean} and RF for the crouch start compared to the other starts (P ≤ 0.05). Significant correlations were found between T_5m and T_start (r = 0.59; P ≤ 0.001), and T_5m and P_max, F_{x_mean} and RF (?0.73 ≤ r ≤ ?0.61; P ≤ 0.001). To conclude, the crouch start resulted in the best performance because T_start was shorter, producing greater P_max, F_{x_mean} with a more forward orientation of the resultant force. Greater KE of the trunk in each start condition demonstrated the role of the trunk in generating forward translation of the centre of mass (CM).     

Upper limb and trunk muscle activity patterns during seated and standing cycling

The objective of this study is to clarify the functional roles of upper limb muscles during standing and seated cycling when power output increases. We investigated the activity of seven upper limb and trunk muscles using surface electromyography (EMG). Power outputs ranged from ~100–700 W with a pedalling frequency of 90 revolution per minute. Three-dimensional handle and pedal forces were simultaneously recorded. Using non-negative matrix factorisation, we extracted muscle synergies and we analysed the integrated EMG and EMG temporal patterns. Most of the muscles showed tonic activity that became more phasic as power output increased. Three muscle synergies were identified, associated with (i) torso stabilisation, (ii) compensation/generation of trunk accelerations and (iii) upper body weight support. Synergies were similar for seated and standing positions (Pearson’s r > 0.7), but synergy #2 (biceps brachii, deltoidus and brachioradialis) was shifted forward during the cycle (~7% of cycle). The activity levels of synergy #1 (latissimus dorsi and erector spinae) and synergy #2 increased markedly above ~500 W (i.e., ~+40–70% and +130–190%) and during periods corresponding to ipsi- and contralateral downstrokes, respectively. Our study results suggest that the upper limb and trunk muscles may play important roles in cycling when high power outputs are required.