Το σούτ στο ποδόσφαιρο δεν γίνεται πιο γρήγορο μετά από προσποίηση

in Ποδόσφαιρο

Sports Biomech. 2011 Mar;10(1):35-45.

Katis AKellis E.

Η αλλαγή κατεύθυνσης είναι μια συνηθισμένη ποδοσφαιρική κίνηση η οποία χρησιμοποιείται για την αποφυγή του αντιπάλου. Πόσο όμως επηρεάζει την επίδοση του σούτ; Ο σκοπός της εργασίας ήταν να μελετήσει τις διαφορές στα κινηματικά χαρακτηριστικά των κάτω άκρων κατά την εκτέλεση σουτ με κουντεπιέ με και χωρίς προσποίηση σε δέκα ερασιτέχνες ποδοσφαιριστές.  Τα αποτελέσματα έδειξαν οτι όταν ο ποδοσφαιριστής προσποιείται με αλλαγή κατεύθυνσης και μετά εκτελεί σουτ, τότε το σουτ είναι πιο αργό (16.73 έναντι 19.78 m/s, p < 0.05). Αυτό οφείλεται σε διαφορετική τοποθέτηση των μελών του σώματος αλλά και υψηλότερη ταχύτητα της ποδοκνημικής (που έρχεται σε τελική επαφή με την μπάλα) όταν προηγηθεί προσποίηση. Σύμφωνα με τα αποτελέσματα αυτά, η βελτίωση της αποτελεσματικότητας του σουτ μέσα στο παιχνίδι απαιτεί προπόνηση στην εκτέλεση σουτ μετά από προσποιήσεις ώστε να επιτευχθεί καλύτερη συναρμογή των κινήσεων και, ως συνέπεια, ένα πιο γρήγορο σουτ.

Sports Biomech. 2011 Mar;10(1):35-45.

Is soccer kick performance better after a «faking» (cutting) maneuver task?

Katis AKellis E.

Department of Physical Education and Sports Sciences of Serres, Aristotle University of Thessaloniki, Serres, Greece. akatis@phed-sr.auth.gr

Abstract

Cutting in soccer is a common skill used to avoid the opponent’s pressure but the potential effects of such a skill on instep kicking performance have not been previously investigated. The purpose of this study was to examine the differences in lower limb biomechanics between straight approach soccer kicks and kicks performed following a cutting maneuver task. Ten young amateur soccer players performed, in a random order, instep kicks after a two-step straight approach run and kicks after a double «faking» cutting maneuver task. The results showed that kicking after a cutting maneuver task displayed significantly lower ball speed values compared with the straight approach instep kicking (16.73 vs. 19.78 m/s, respectively; p < 0.05). Moreover, analysis of variance showed significant differences between the two kicking conditions in ankle, knee and hip joint displacements. The present study indicated that performing instep kicks after a double-cutting maneuver reduces ball and foot speed probably due to increasing joint frontal and transverse plane rotations. Improvements in the performance of the cutting maneuver task through training might result in better transfer of energy and speed to the kicking task thus permitting players to perform more powerful kicks under realistic game conditions.

 

 

 

Οστεοαρθρίτιδα και άρση απο καρέκλα

in Κλινική εμβιομηχανική

J Electromyogr Kinesiol. 2011 Oct;21(5):689-94.

Neuromuscular efficiency during sit to stand movement in women with knee osteoarthritis.

Οι γυναίκες με οστεοαρθρίτιδα είναι λιγότερο αποτελεσματικές κατά την άρση απο καρέκλα

Patsika GKellis EAmiridis IG.

Source

Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Thessaloniki, Greece. gpatsika@phed-sr.auth.gr

Abstract

The purpose of this study was to investigate the neuromuscular efficiency of women with knee osteoarthritis (OA) when performing a sit-to-stand movement and during maximum strength efforts. Twelve women with unilateral knee OA (age 60.33±6.66 years, height 1.61±0.05 m, mass 77.08±9.2 kg) and 11 controls (age 56.54±5.46 years, height 1.64±0.05 m, mass 77.36±13.34 kg) participated in this study. Subjects performed a sit-to-stand movement from a chair while position of center of pressure and knee angular speed were recorded. Furthermore, maximal isokinetic knee extension and flexion strength at 60°/s, 120°/s and 150°/s was measured. Surface, electromyography (EMG) from the biceps femoris (BF), vastus lateralis (VL) and vastus medialis (VM) was recorded during all tests. Analysis of variance (ANOVA) showed that during the sit-to-stand OA group demonstrated significantly lower knee angular speed (44.49±9.61°/s vs. 71.68±19.86°/s), a more posterior position of the center of pressure (39.20±7.02% vs. 41.95±2.49%) and a higher antagonist BF activation (57.13±20.55% vs. 32.01±19.5%) compared with controls (p<0.05). Further, women with knee OA demonstrated a lower Moment-to-EMG ratio than controls in extension and eccentric flexion at 60°/s and 150°/s, while the opposite was found for concentric flexion at 60°/s (p<0.05). Among other factors, the slower performance of the sit-to-stand movement in women with OA is due to a less efficient use of the knee extensor muscles (less force per unit of EMG) and, perhaps, a higher BF antagonist co-activation. This may lead subjects with OA to adopt a different movement strategy compared with controls.

Οι τυφλοί ποδοσφαιριστές έχουν υψηλή τεχνική σουτ

in Ποδόσφαιρο

Adapt Phys Activ Q. 2011 Jul;28(3):251-66.

Differences in soccer kick kinematics between blind players and controls.

Οι τυφλοί ποδοσφαιριστές εμφανίζουν παρόμοια κινηματικά χαρακτηριστικά του σουτ σε σχέση με υγιείς

Giagazoglou PKatis AKellis ENatsikas C.

Source

Laboratory of Neuromechanics, Department of Physical Education and Sports Science at Serres, Aristotle University of Thessaloniki, Greece.

Abstract

The purpose of the current study was to examine the kinematic differences during instep soccer kicks between players who were blind and sighted controls. Eleven male soccer players who were blind and nine male sighted performed instep kicks under static and dynamic conditions. The results indicated significantly higher (p < .05) ball speed velocities (20.81m/sec) and ball/foot speed ratio values (1.35) for soccer players who were blind during the static kick compared with sighted players (16.16m/sec and 1.23, respectively). Significant group effect on shank and foot angular velocity was observed during the static kicking condition (p < .05), while no differences were found during the dynamic kicking condition (p > .05). Despite the absence of vision, systematic training could have beneficial effects on technical skills, allowing athletes who are blind to develop skill levels comparable to sighted athletes.

Οι ολυμπιακές άρσεις βελτιώνουν την επίδοση χωρίς να αλλάζουν τη μυϊκή συνενεργοποίηση

in Προπόνηση

J Strength Cond Res. 2011 Oct 12. [Epub ahead of print]

OLYMPIC-WEIGHT LIFTING TRAINING CAUSES DIFFERENT KNEE MUSCLE – CO ACTIVATION ADAPTATIONS COMPARED WITH TRADITIONAL WEIGHT TRAINING.

Η προπόνηση με ολυμπιακές άρσεις προκαλεί διαφορετικές προσαρμογές στην συνενεργοποίηση των μυών του γονάτου σε σχέση την παραδοσιακή προπόνηση με βάρη

Arabatzi FKellis E.

Source

Laboratory of Neuromechanics, Department of Physical Education and Sport Science, Aristotle University of Thessaloniki at Serres, Greece.

Abstract

The purpose of this study was to compare the effects of an Olympic-weight lifting (OL), and traditional weight (TW) training program on muscle- co-activation around the knee joint during vertical jump tests. Twenty six males were assigned randomly to 3 groups: the OL (n=9), the TW (n=9) and Control (C) groups (n=8). The experimental groups trained 3 days a week for eight weeks. Electromyographic (EMG) activity from rectus femoris (RF) and Biceps Femoris (BF), sagital kinematics, vertical stiffness, maximum height and power were collected during squat (SJ), counter movement (CMJ) and drop (DJ), jumping before and after training. Knee muscle co-activation (CI) index was calculated for different phases of each jump by dividing the antagonist EMG activity by the agonist. Analysis of variance showed that the CI recorded during the pre-activation and eccentric phases of all jumps increased in both trainings groups. The OL group showed a higher stiffness and jump height adaptation than the TW group (P <0.05). Further, the OL showed a decrease or maintenance of the CI recorded during propulsion phase of the CMJ and DJs which is in contrast to the increase in the CI observed after TW training (P < 0.05). The results indicated that the altered muscle activation patterns about the knee, coupled with changes of leg stiffness differ between the two programs. The OL program improves jump performance via a constant CI while the TW training caused an increased CI, probably to enhance joint stability.

Η τενόντια ραφή του ημιτενοντώδη επηρεάζει τον τρόπο που συσπάται

in Featured, Οπίσθιοι Μηριαίοι - Αρχιτεκτονική

Cells Tissues Organs. 2011 Aug 9. [Epub ahead of print]

In vivo and in vitro Examination of the Tendinous Inscription of the Human Semitendinosus Muscle.

Kellis EGalanis NNatsis KKapetanos G.

Source

Laboratory of Neuromechanics, Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Serres, Greece.

Abstract

The aim of this study was to examine the tendinous inscription (TI) of the human semitendinosus (ST) muscle using dissection (cadavers) and ultrasound (in vivo). Ultrasonography (US) scans were taken in 18 young males at rest and at maximum voluntary contraction (MVC). Further, the ST was dissected and removed from its origins in 10 cadaveric specimens (5 cadavers). The cadaveric long arm of the TI was 6.67 ± 0.64 cm (6.45 ± 1.21 in US) while the shorter arm was 2.39 ± 0.38 cm (1.99 ± 0.75 in US). The angle formed by the two TI arms ranged from 53.19 (US) to 56.05° (cadavers) while more superficial fascicles intersected the inscription at significantly higher angles (range 31.98 ± 6.15 to 34.69 ± 7.71°) compared with deeper fascicles (p < 0.05). Fascicle length did not differ between compartments, but it was significantly smaller in superficial compared with deeper layers (p < 0.05). With the exception of the angle between the TI arm and the deep aponeurosis, all measured angles as well as the length of the long arm of the TI increased significantly from rest to MVC (p < 0.05). The role of the TI probably lies in the local interconnections with the fascicles of either compartment, which upon contraction is such that the ST muscle contracts as one muscle. However, the TI arm morphology changes from rest to MVC, indicating a nonuniform displacement of the TI, mainly between the superficial and deeper layers of the muscle.

Copyright © 2011 S. Karger AG, Basel.

Η πλειομετρική προπόνηση σε κεκλιμένο επίπεδο αυξάνει την επίδοση

in Προπόνηση

Eur J Appl Physiol. 2011 Oct 29. [Epub ahead of print]

Incline plyometrics-induced improvement of jumping performance.

Kannas TMKellis EAmiridis IG.

Source

Laboratory of Neuromechanics, Department of Physical Education and Sports Sciences at Serres, Aristotle University of Thessaloniki, Serres, Greece, thkannas@phed-sr.auth.gr.

Abstract

The aim of this study was to examine the effects of incline plyometrics training on muscle activation and architecture during vertical jumping and maximum strength. Twenty male participants were divided in two training groups which followed after a 4 week training program. The incline plyometrics group (n = 10) trained by performing consecutive jumps on an inclined surface (15°) while the plane plyometrics (PP) group (n = 10) performed the same jumps on a plane surface. Both groups trained four times per week and performed 8 sets of 10 jumps in each session. Subjects performed squat jumps, counter movement jumps and drop jumps (DJ) prior to and immediately after the training period, while the electromyographic activity of the medial gastrocnemius (MGAS) and tibialis anterior muscles and the architecture of MGAS were recorded. Maximal isokinetic and isometric strength of the plantar flexors were performed. Analysis of variance showed that only the IP group improved fast DJ height performance by 17.4 and 14.4% (20 and 40 cm, p < 0.05). This was accompanied by a significantly higher MGAS activity during the propulsion phase (24% from 20 cm and 50% from 40 cm, p < 0.05) of the DJ and a longer working fascicle length (5.08%, p < 0.05) compared with the PP group. There were no significant changes in isokinetic and isometric strength of the plantar flexors after training for both groups. The increase of jumping performance, after incline plyometrics should be taken into consideration by coaches, when they apply hopping exercise to improve explosiveness of the plantar flexors.

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