Differences in the utilisation of active power in squat and countermovement jumps     

Damián Ferraro  Gabriel Fábrica 《European Journal of Sport Science》2017,17(6):673-680

The aim of this article was to understand how active power is used in squat and countermovement jumps. A simple empirical model comprising a mass, a spring, an active element and a damper, together with an optimisation principle, was used to identify the mechanical factors that maximise performance of jumps without countermovement (squat jumps, SJ) and with countermovement (CMJ). Twelve amateur volleyball players performed SJ from two initial positions and CMJ with two degrees of counterbalancing, while kinematic data were collected (jump height, push-off duration and position of the centre of mass). The model adjusted well to real data of SJ through all the impulse phase, and slightly less adequately at the end of this phase for CMJ. Nevertheless, it provides a satisfactory explanation for the generation and utilisation of active power for both type of jumps. On average, the estimated power of the active elements, the spring, and the damper were greater in the SJ. Based upon the result obtained with this model, we suggest that active power is best evaluated with SJ. The reason for this is that, during this kind of jump, the elements associated with the damper consume much of the energy produced by the active elements. The participation of the elements that consume the energy generated by the active elements is less in CMJ than in SJ, allowing for a better utilisation of this energy. In this way it is possible to achieve a better performance in CMJ with less active power.  相似文献   

A scale-based approach to interdisciplinary research and expertise in sports     

Jorge Ibáñez-Gijón  Martinus Buekers  Antoine Morice  Guillaume Rao  Nicolas Mascret  Jérome Laurin 《Journal of sports sciences》2017,35(3):290-301

After more than 20 years since the introduction of ecological and dynamical approaches in sports research, their promising opportunity for interdisciplinary research has not been fulfilled yet. The complexity of the research process and the theoretical and empirical difficulties associated with an integrated ecological-dynamical approach have been the major factors hindering the generalisation of interdisciplinary projects in sports sciences. To facilitate this generalisation, we integrate the major concepts from the ecological and dynamical approaches to study behaviour as a multi-scale process. Our integration gravitates around the distinction between functional (ecological) and execution (organic) scales, and their reciprocal intra- and inter-scale constraints. We propose an (epistemological) scale-based definition of constraints that accounts for the concept of synergies as emergent coordinative structures. To illustrate how we can operationalise the notion of multi-scale synergies we use an interdisciplinary model of locomotor pointing. To conclude, we show the value of this approach for interdisciplinary research in sport sciences, as we discuss two examples of task-specific dimensionality reduction techniques in the context of an ongoing project that aims to unveil the determinants of expertise in basketball free throw shooting. These techniques provide relevant empirical evidence to help bootstrap the challenging modelling efforts required in sport sciences.  相似文献   

Are gait characteristics and ground reaction forces related to energy cost of running in elite Kenyan runners?     

J. Santos-Concejero  N. Tam  D. R. Coetzee  J. Oliván  T. D. Noakes  R. Tucker 《Journal of sports sciences》2017,35(6):531-538

The aim of this study was to determine whether gait cycle characteristics are associated with running economy in elite Kenyan runners. Fifteen elite Kenyan male runners completed two constant-speed running sets on a treadmill (12 km ·h^?1 and 20 km ·h^?1). VO₂ and respiratory exchange ratio values were measured to calculate steady-state oxygen and energy cost of running. Gait cycle characteristics and ground contact forces were measured at each speed. Oxygen cost of running at different velocities was 192.2 ± 14.7 ml· kg^?1· km^?1 at 12 km· h^?1 and 184.8 ± 9.9 ml· kg^?1· km^?1 at 20 km· h^?1, which corresponded to a caloric cost of running of 0.94 ± 0.07 kcal ·kg^?1·km^?1 and 0.93 ± 0.07 kcal· kg^?1· km^?1. We found no significant correlations between oxygen and energy cost of running and biomechanical variables and ground reaction forces at either 12 or 20 km· h^?1. However, ground contact times were ~10.0% shorter (very large effect) than in previously published literature in elite runners at similar speeds, alongside an 8.9% lower oxygen cost (very large effect). These results provide evidence to hypothesise that the short ground contact times may contribute to the exceptional running economy of Kenyan runners.  相似文献   

Light-load maximal lifting velocity full squat training program improves important physical and skill characteristics in futsal players     

Julio Torres-Torrelo  Juan José González-Badillo 《Journal of sports sciences》2017,35(10):967-975

This study aimed to compare the effect of 6 weeks of resistance training or combined resistance training and change of direction exercises on physical performance and motor skills in futsal players. Thirty-four futsal players were divided into full squat group (SG, n = 12), combined full squat and change of direction exercises group (S+CDG, n = 12) and control group (CG, n = 10). The resistance training for SG consisted of full squat with low load (~45–58% 1RM) and low volume (4–6 repetitions), whereas the S+CDG performed the same resistance training program combined with loaded change of direction. Sprint time in 10 and 20 m, change of direction test, countermovement vertical jump (CMJ) height, maximal strength and force–velocity relationship in full squat exercise, kicking speed ball (BS_mean) and repeated sprint ability (RSA_mean) were selected as testing variables. Both experimental groups showed significant improvements for CMJ, BS_mean and all strength parameters. Only SG resulted in significant sprint gains, whereas S+CDG also achieved significant improvements in RSA_mean. The CG remained unchanged after training period. No significant differences were found between both experimental groups. These findings suggest that only 12 sessions of either lightweight resistance training alone, lifting the load at maximal intended velocity or combined with change of direction exercises is enough to improve several physical and skills capacities critical to futsal performance in adult players.  相似文献   

Association of different types of playing surfaces with bone mass in growing girls     

Esther Ubago-Guisado  Jorge García-Unanue  Jorge López-Fernández  Javier Sánchez-Sánchez  Leonor Gallardo 《Journal of sports sciences》2017,35(15):1484-1492

The aim of this cross-sectional study was to compare bone mass in young female athletes playing ball games on different types of playing surfaces. About 120 girls, 9–13 years of age (10.6 ± 1.5 years old Tanner I–III) were recruited and divided into prepubertal and pubertal groups. The sample represented 3 groups of athletes: soccer (N = 40), basketball (N = 40), and handball (N = 40); and 6 different playing surfaces (soccer – ground, soccer – artificial turf, basketball – synthetic, basketball – parquet, handball – synthetic, and handball – smooth concrete). Total and regional body composition (bone mass, fat mass, and lean mass) were measured by dual-energy X-ray absorptiometry (DXA). The mechanical properties of the surfaces (force reduction, vertical deformation, and energy return) were measured with the Advanced Artificial Athlete (Triple A) method. The degree of sexual development was determined using Tanner test. The pubertal group showed that soccer players on the ground, basketball players on synthetic, and handball players on smooth concrete had higher values of bone mineral content (BMC) and bone mineral density (BMD) (P < 0.05) than the soccer players on the artificial turf, basketball players on parquet, and handball players on synthetic. In conclusion, a hard playing surface, with less vertical deformation and force reduction, and greater energy return, is associated with higher levels of BMD and BMC in growing girls, regardless of the sport they practice.  相似文献   

Sexual dimorphism in bone–muscle relationship in young adults     

Vera Zymbal  Kathleen F. Janz  Fátima Baptista 《Journal of sports sciences》2017,35(24):2433-2438

The purpose of this study was to analyse associations between lean soft tissue (LST), a surrogate of skeletal muscle mass and key fracture-related geometric characteristics of the proximal femur. Moreover, we examined the role that muscle played on the proximal femur geometry in response to physical activity (PA). Participants were 83 young adults. Leg LST (exposure) was assessed by dual energy X-ray absorptiometry (DXA). Proximal femur geometry was derived from a left hip DXA scan. Geometric variables (outcomes) included the femoral neck axis length (FNAL), the femoral neck width (FNW), the neck–shaft angle and FNW|FNAL (an index of robustness). PA was evaluated by accelerometry. Linear regression was used to analyse relationships. Additional exposure variables included body height and mass. In males, leg LST explained 17.4% of variation in FNAL (P < 0.001) and 15% in FNW (P = 0.015). In females, it explained 8.8% of the variance in FNAL (P = 0.020). Associations remained significant in males, but not in females, when vigorous PA was added to the models. These results suggest that public health approaches to promote PA may be particularly important in females since vigorous PA seems to convey advantages in femur geometry and consequently in bone strength.  相似文献   

Circadian rhythm effect on physical tennis performance in trained male players     

Álvaro López-Samanes  Diego Moreno-Pérez  José L. Maté-Muñoz  Raúl Domínguez  Jesús G. Pallarés  Ricardo Mora-Rodriguez 《Journal of sports sciences》2017,35(21):2121-2128

To determine the effect of circadian rhythm on neuromuscular responses and kinematics related to physical tennis performance, after a standardised warm-up, 13 highly competitive male tennis players were tested twice for serve velocity/accuracy (SVA), countermovement vertical jump (CMJ), isometric handgrip strength (IS), agility T-test (AGIL) and a 10-m sprint (10-m RUN). In a randomised, counter-balance order, tennis players underwent the test battery twice, either in the morning (i.e., AM; 9:00 h) and in the afternoon (i.e., PM; 16:30 h). Paired t-tests were used to analyse differences due to time-of-day in performance variables. Comparison of morning versus afternoon testing revealed that SVA (168.5 ± 6.5 vs. 175.2 ± 6.1 km · h^?1; P = 0.003; effect size [ES] = 1.07), CMJ (32.2 ± 0.9 vs. 33.7 ± 1.1 cm; P = 0.018; ES = 1.46), AGIL (10.14 ± 0.1 vs. 9.91 ± 0.2 s; P = 0.007; ES = 1.23) and 10-m RUN time (1.74 ± 0.1 vs. 1.69 ± 0.1 s; P = 0.021; ES = 0.67) were significantly blunted during the morning testing. However, IS was not affected by time-of-day (P = 0.891). Thus, tennis performance may be reduced when competing in the morning in comparison to early evening. Therefore, coaches and tennis players should focus on schedule the SVA, power, speed and agility training sessions in the afternoon.  相似文献   

Towards a Cultural Understanding of the Disability and Deaf Experience: A Content Analysis of Introductory Multicultural Education Textbooks     

John R. Johnson  Jesús Nieto 《Multicultural Perspectives》2013,15(3):33-43

This paper reports the findings of a simple normative content analysis of 11 multicultural education textbooks to determine the extent to which disability and deaf culture are represented. In addition, this study examines multicultural education textbooks to assess the extent to which perspectives of members of the disability and deaf communities are represented in the discourse about disabled and deaf persons. Results indicate that on average less than 1% of the total pages of text reviewed addressed or mentioned disability or deaf culture. Of these, it was found that on average about 6% of the pages addressed disability or deaf culture. In addition, inaccurate information was presented and perspectives were often not informed by a substantial body of literature that has emerged in the field of disability studies. It was found that multicultural education textbooks rely heavily on information about persons with disabilities from Special Education that may not be widely accepted by disabled or deaf persons. A follow-up paper examines the implications of the exclusion of disabled and deaf persons and their perspectives from the discourse about the shared and collective disability and deaf experience in favor of a dominant perspective widely held by the nondisabled professional community. Questions are raised about whether this is consistent with the values and goals of multicultural education and teaching. A rationale and recommendations are proposed for engaging disabled and deaf persons about their shared and collective experience and for promoting cultural competence and proficiency with respect to the disability and Deaf experience in multicultural education.  相似文献   

Facilitating Intercultural Communication in Parent–Teacher Conferences: Lessons From Child Translators     

Inmaculada M. García–Sánchez  Marjorie Faulstich Orellana  Megan Hopkins 《Multicultural Perspectives》2013,15(3):148-154

In this article Abraham Lincoln is considered as an alternative to the usual type of patriot's hero. He reminds us of our great historical failings. He remains a figure of controversy, a national hero in only some corners of society. He is the heroic President who serves as the first compassionate defender of the downtrodden, and he is a hero in those subcultures as well. Lincoln's treatment in the movies is discussed, focusing particularly on the recent movie Lincoln. Lincoln is seen as a match for the usual movie hero. His famous immunity to casual treatment in popular culture is discussed as well.  相似文献   

The organization of educational research in the Czechoslovak Socialist Republic     

Emilie Langová  Anna Střížová 《International Review of Education/Internationale Zeitschrift für Erziehungswissenschaft/Revue internationale l'éducation》1962,8(1):78-81

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