Analysis of elbow muscle strength parameters in Brazilian jiu-jitsu practitioners     

Bruno Follmer  Rodolfo André Dellagrana  Luis Antonio Pereira de Lima  Walter Herzog 《Journal of sports sciences》2017,35(23):2373-2379

Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s^-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.  相似文献   

Effects of dynamic resistance training on fascicle length and isometric strength     

Alegre LM  Jiménez F  Gonzalo-Orden JM  Martín-Acero R  Aguado X 《Journal of sports sciences》2006,24(5):501-508

The aims of this study were to assess changes in muscle architecture, isometric and dynamic strength of the leg extensor muscles, resulting from dynamic resistance training, and the relationships between strength and muscle architecture variables. The participants (n = 30) were randomly assigned to one of two groups. The training group (n = 16; age 21.8 +/- 2.3 years, body mass 74.8 +/- 9.2 kg, height 1.75 +/- 0.08 m) performed dynamic resistance training for 13 weeks. The control group (n = 14; age 19.9 +/- 1.5 years, body mass 74.0 +/- 8.5 kg, height 1.76 +/- 0.05 m) did not perform any resistance training. Maximal dynamic and isometric strength were tested in both groups, before and after the training period. The members of the training group used the free-weight squat lift (90 degrees ) as their training exercise. The concentric phase of the squat was performed explosively. Skeletal muscle architecture of the vastus lateralis was visualized using ultrasonography. At the end of the study, significant increases in vastus lateralis muscle thickness (+6.9%, P < 0.001), fascicle length (+10.3%, P < 0.05), one-repetition maximum (+8.2%, P < 0.05), rate of force development (+23.8%, P < 0.05) and average force produced in the first 500 ms (+11.7%, P < 0.05) were seen only in the training group. Adaptations to the muscle architecture in the training group limited the loss of fibre force, and improved the capacity for developing higher velocities of contraction. The architectural changes in the training group were similar to those seen in studies where high-speed training was performed. In conclusion, dynamic resistance training with light loads leads to increases in muscle thickness and fascicle length, which might be related to a more efficient transmission of fibre force to the tendon.  相似文献   

Postural control and physiological responses to a simulated match in U-20 judo competitors     

Luis Santos  Javier Fernández-Río  Eliseo Iglesias-Soler  Miguel Blanco-Traba  Markus Due Jakobsen  Vicente González-Díez 《Sports biomechanics / International Society of Biomechanics in Sports》2020,19(3):281-294

Abstract

The aim was to evaluate the effects of judo combat on the athletes’ postural control (PC) and physiological loading before, during and after a simulated match. Seventeen under-20 regional and national level athletes completed one modified 7-min match. At baseline, during the combat (3rd and 7th minutes) and 2-min post-match centre of pressure (CoP) parameters were assessed. Heart rate (HR), blood lactate (BLa) and rating of perceived exertion (RPE) and local RPE (LRPE) were collected. Significant increments were observed in CoP mean positioning and velocity at 3rd and 7th minutes, but the CoP deviation in both axes was unaffected. HR and BLa were elevated at 3rd and 7th minutes, and they remained elevated 2-min post-match. However, CoP returned to baseline 2-min post-match. RPE was elevated at 3rd and 7th minutes and the greatest effort was displayed in the Deltoid and Quadriceps. Thus, one simulated judo match stimulates a significant metabolic response and balance is degraded, with the greatest effects on the anterior–posterior axis and it recovers to baseline level after 2 min of passive rest. The physiological load cannot be regarded as a potential predictor variable of CoP. Overall, a judo match predominantly affects the upper body than the other body parts.  相似文献   

Gonadal hormones may predict structural bone fragility in elite female soccer player     

Charlotte Lanhers  Daniel Courteix  João Valente-Dos-Santos  Beatrice Ferry  Luis Gracia-Marco  Bruno Pereira 《Journal of sports sciences》2020,38(7):827-837

ABSTRACT

Purpose: This study determined the impact of menstrual status on bone tissue in elite post-pubertal female soccer players over an entire season.

Methods: Fifty-one elite female soccer players participated. At baseline, forty-one were assigned to the low hormonal androgenic profile (low-HAPL) and 10 to the high hormonal androgenic profile (high-HAPL).

Results: An 8-month training program led to increased bone mineral density content (p<0.05). The low-HAPL athletes improved the Narrow neck average cortical thickness (ACT) by 1.4% and reduced the corresponding Buckling ratio (BR) by 2.6%, thus decreasing the fracture risk (p<0.05). The high-HAPL athletes decreased the Narrow neck ACT by 5.4% and increased the BR by 2.6%, increasing fracture risk (p<0.05). Differences were assigned as being “very likely beneficial” for the low-HAPL athletes, supported by very large (d=3.41) and large (d=1.58) effect sizes for the Narrow neck ACT and BR, respectively.

Conclusion: A season of soccer training has induced bone geometry improvements in adolescent females. Bone health parameters improved in the two clusters. However, high-HAPL athletes decreased its resistance to loading compare to low-HAPL athletes. Even if female players do not present clinical symptoms related to their hormonal status, sport medicine physicians should pay attention to their structural bone fragility.  相似文献   

Book review: The first century of the International Commission on Mathematical Instruction     

Luis Rico 《Educational Studies in Mathematics》2010,73(2):205-210

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The construction of parents and teachers as agents for the improvement of municipal schools in Chile     

Carmen Montecinos  Vicente Sisto  Luis Ahumada 《比较教育学》2010,46(4):487-508

This article examines how teachers and parents in 10 municipal schools serving students growing up under conditions of social vulnerability represented themselves, and others, as valid agents for charting school improvement. In four schools parents and teachers saw each other as trustworthy and collaborating to provide an education that could transform students’ life chances. In the other six schools, social relations were marked by distrust, staff constructed students as lacking the resources necessary to benefit from a rigorous academic programme, and parents in leadership positions shared with teachers the belief that school failure could largely be attributed to uncommitted parents. These results suggest that the impact of quality assurance policies tends to be associated with the social capital of municipal schools, thus educational policy needs to consider developing and strengthening social capital within schools.  相似文献   

The path to information in the public domain: Official publications in Spain     

Luis Fernando Ramos SimónAuthor Vitae  Iuliana Botezan 《Government Information Quarterly》2010

Official publications are aimed towards editing and spreading the messages created by governments and other bodies of the public domain. At the beginning, the aim of this activity is twofold: on the one hand, fulfilling the principle of publicity of the norms, as it constitutes a basis for the efficiency of those, and, on the other hand, fulfilling a general function of information about the activities of public authorities. As the action of government generalises, this function of communication between those governing and those governed has extended to other fields of activity, thus, free and pay materials, both printed and electronic, are published.  相似文献   

Making It Work for Everyone: An Evolving Reference Service     

Jonquil D. Feldman  Emme Lopez  Christine S. Gaspard  Karen D. Barton  Luis F. Barcenes III 《Medical reference services quarterly》2018,37(1):10-18

At an academic health science center, librarians identified problems, weaknesses, and strengths in reference services. The on-call reference schedule was discontinued and a question flowchart was developed for circulation staff. Only research questions were referred to librarians, who would respond if available. Circulation staff perceived the unscheduled, voluntary model was not working well for the patrons or the staff. After two months, the schedule was reinstated with a hybrid version of the previous on-call format. In the process of changing the service model, the library staff also underwent a cultural change.  相似文献   

The anatomy of information cascades in the classroom: An observational study     

Luis M. Vaquero  Luis Rodero-Merino  Félix Cuadrado 《British journal of educational technology : journal of the Council for Educational Technology》2019,50(1):371-384

Online learning platforms offer students the option of sharing content. They have become common tools in many universities over the last 10 years. But there is little information about how content spreads in the classroom, ie, how information cascades appear and evolve and what factors are relevant for the formation of cascades. This work analyses information cascades in the classroom, bringing new insights on student learning: students do not share much content, they prefer to share the content they find themselves as opposed to professor-given content, they share more data towards the end of the course and they do it in bursts. The paper also reveals different behaviour by high-performing students: their interactions are distributed more evenly over the term, their behaviour is more stable and they tend to share documents faster than low-performing students. Documents with high information tend to be less shared. Documents with fewer well-known entities are also shared fewer times. Paradoxically, high-performing students exchange more documents with high information, compared to mid- and low-performing students.  相似文献   

Communication's quest for whiteness: the racial politics of disciplinary legitimacy     

Bryan J. McCann  Ashley Noel Mack  Rico Self 《传播与批判/文化研究》2020,17(2):243-252

ABSTRACT

This essay examines communication's historical anxieties regarding disciplinary legitimacy as an investment in whiteness. We argue that such anxieties are predicated upon a normative ideal of citizenship. As such, rhetorics of disciplinary legitimacy enact white civil society's originary exclusion, which is antiblackness. To illuminate the ways antiblackness finds expression in these anxieties, we engage the field's lengthy archive of public musings regarding legitimacy to trace the rhetorical workings of antiblackness therein.  相似文献