1,721,028 research outputs found
L’asimmetria nello sprint: analisi tridimensionale su atleti top level. Uno studio pilota.
No full textIl successo o meno di uno sprinter durante la stagione sportiva è legato non solo ad una
corretta pianificazione dei mezzi e dei contenuti dell’allenamento, ma anche alla propria integrità
fisica. Diventa prioritario pertanto da parte dell’allenatore cercare di prevenire gli infortuni del
proprio atleta. A questo proposito, tra gli infortuni più frequenti nello sprint risultano quelli ai
muscoli ischiocrurali. Secondo la letteratura più recente, le cause più probabili di tali infortuni
sono legate ad uno squilibrio di forza tra quadricipite e ischiocrurali, ad un errato automatismo
tecnico o ad un comportamento asimmetrico degli arti inferiori durante la corsa. Proprio su
quest’ultima causa si stanno concentrando le ricerche di molti studiosi e si inserisce anche questo
studio pilota che analizza, tramite l’optojump ed una ricostruzione tridimensionale del movimento
(SIMI Motion System), i parametri cinematici lineari ed angolari nonché i dati temporali di 4
velocisti di livello nazionale durante una prova di corsa alla massima velocità. Le maggiori
asimmetrie (indice di asimmetria SA superiore al 15%) si sono riscontrate soprattutto nei ROM
articolari di ginocchio e caviglia e nella massima estensione dell’anca. I risultati sembrano
dimostrare come l’asimmetria possa configurarsi sia come causa, ma anche come effetto degli
infortuni agli ischiocrurali. A rinforzo di questa ipotesi, uno dei soggetti analizzati, che
successivamente all’elaborazione dei dati, ha mostrato diversi parametri asimmetrici, proprio
durante la sessione di acquisizione ha accusato un infortunio al comparto posteriore della coscia.
Ai fini pratici, pertanto, potrebbe essere importante fotografare la situazione tecnica e fisica dello
sprinter all’inizio della nuova stagione agonistica, in modo da provare a ripristinare, qualora ce ne
fosse bisogno, una corretta simmetria di corsa prima di incominciare a sottoporre l’atleta a nuovi
carichi di allenamento. Per far sì però che la ricerca possa effettivamente fornire agli allenatori ed
agli atleti dei dati generalizzabili sull’asimmetria e sul collegamento tra questa e gli infortuni agli
ischiocrurali, sono necessari ancora molti studi che coinvolgano un numero maggiore di atleti,
differenziandone i livelli prestativi, seguendone la carriera longitudinalmente ed analizzando
anche le possibili differenze di genere
A New Method for Evaluating the Reactive Strength Index in Track and Field Sprinting: Relationships with Muscle Architecture
Full text linkThe aim of the present study was to assess a new reactive strength index (RSI RUN) based on contact time and stride length measured in sprint running and then to correlate this index with sprint performance, muscle architecture and echo intensity of the vastus lateralis. Participants included ten elite and sub-elite sprinters (age 24.4 ± 3.1 years, height 177.5 ± 7.7 cm, mass 69.8 ± 11.7 kg) who were tested with a vertical drop jump (VDJ) and a horizontal drop jump (HDJ) from a 30 cm high box, a 20 m straight-leg running drill (SLR) and a 60 m sprint. A nearly perfect correlation (r = from −0.90 to −0.96, p < 0.01) was detected between RSI RUN and sprint performance (30 m, 60 m and 100 m sprint time), and a very large correlation (r = from −0.72 to −0.77, p < 0.05) was found between the
traditional RSI from vertical drop jump (RSIDJV) and sprint performance. In addition, the RSI RUN was more correlated to sprint performance than other RSI indices studied in previous research. The echo intensity of the vastus lateralis (VLEI) was largely correlated with maximum running speed
(r = from 0.76 to 0.87, p < 0.05) and the RSI RUN (r = −0.80, p < 0.05). No significant correlations were noted between echo intensity and other RSIs. In conclusion, the RSI RUN and VLEI seem to be good predictors for track and field sprinting performance
Sprint start kinematics during competition in elite and world-class male and female sprinters
No full textThe start kinematics has been reported to differ between male and female sprinters. This study aimed to determine whether kinematic differences between the sexes are attributable to an effect of sex per se, or rather to the absolute performance level of the sprinters, quantified by the 100-m time. A total of 20 sprinters (10 M, 10 F), including world-class and elite athletes, were assessed. Start phases from the “set” position to the first two steps were analysed. Linear regression analyses showed a few significant differences between sexes when taking into account the effect of performance level: M had shorter pushing phase duration, higher horizontal velocity at block clearing, and shorter contact times of the first two steps. Conversely, the performance level affected most of the examined parameters: faster sprinters showed the centre of mass (CM) closer to the ground and a more flexed front knee in the “set” position, longer pushing phase duration, lower vertical velocity of the CM at block clearing, and longer contact times and shorter flight times in the first two steps. These findings suggest that the start kinematics is only partially affected by the sex of sprinters, whereas a bigger role is played by their performance level
Biomechanical analysis of the giant slalom turn in skiers of different performance level.
No full textAnalisi cinematica della tecnica rotatoria nel getto del peso: confronto tra modelli tecnici di atleti di categorie diverse.
Full text linkThe goal of this study is of comparing athletes belonging to youth and senior categories, during the execution of the rotatory technique of shot put, and comparing them with the values recorded in literature for top level athletes, with the aim of observing how the most important kinematic parameters evolve and trying to understand the reason why since many years senior Italian athletes are no more at the top in the most important international events. The videos of the first two athletes, executing the rotatory technique, were acquired at the Italian Youth and Senior Championships. Through the three-dimensional system SIMI Motion (Simi Reality Motion Systems GmbH, Unterschleissheim, Germania) the time and kinematic variables of the throw were identified. The results show that young athletes have a technical incorrect behaviour in comparison with expert athletes, especially as to the body position, in the phases preceding the tool release. This study can offer to coaches some suggestions to try to correct some of the outlined
individual mistakes
Muscle activation during push-up exercise under stable and instable conditions
No full textBACKGROUND: Push up exercise is a popular and common way of strengthening the upper body in clinical, fitness and sport fields. Recently, trainers and researchers suggest to perform this exercises under unstable condition with specific tools, in order to increase muscle activation. PURPOSE: The aim of this study is to investigate the electromyographic activity (EMG) of shoulder and trunk muscles during 4 different kind of isometric push up exercises performed with elbow flexed and extended.
METHODS: Ten healthy subjects volunteered for the study. Three unstable conditions (TRX, BALL, SKIMMY) and one stable condition (STEP) for two different elbow joint angles (90° flexion – FLEX ; full extension - EXT) were tested during 5 seconds isometric push ups. EMG was recorded for Anterior Deltoids (DA), Pectoralis Major (GP), Triceps Brachialis (TRI), Latissimus Dorsi (GD), Rectus Abdomins (RA), Obliquus Externus (OE). Data were processed in order to calculate EMG Root Mean Square (RMS) and normalize to stable condition (Step).
CONCLUSIONS: All unstable conditions show higher muscle activity in both joint angle positions compared to stable condition. In particular, TRX evidences the highest EMG data in FLEX and EXT condition: TRX is higher than BALL, STEP and SKIMMY in EXT condition (p<0.01) and higher than STEP and SKIMMY (p<0.01) in FLEX condition. TRB, RA and OE are the most activated muscles in all conditions for both FLEX and EXT with different values related to specific tools. GP, DA and GD are higher in FLEX than EXT (p<0.01) while RA is higher in EXT angle compared to FLEX (p<0.05).
These findings suggest that adding instability is a good way to improve trunk muscle activity in both joint angle positions, while shoulder muscle activity is more related to elbow condition
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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