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Both an elaborate coordination of the hand grip force ( G ; normal component of force acting at the digits–object contact area) and load force ( L ; tangential component), and the role of cutaneous afferents in G – L coordination have been well documented in a variety of manipulation tasks. However, our recent studies revealed that G – L coordination deteriorates when L consecutively changes direction (bidirectional tasks; e.g., when vigorously shaking objects or using tools). The aim of the study was to distinguish between the possible role of the synergy of hand grip and arm muscles (exerting G and L , respectively) and the role of cutaneous afferent input in the observed phenomenon. Subjects ( N = 14) exerted sinusoidal L pattern in vertical direction against an externally fixed device in trials that gradually changed from uni- to fully bidirectional. In addition, a manipulation of an external arm support decoupled L measured by the device (and, therefore, recorded by the cutaneous receptors) from the action of arm muscles exerting L . The results revealed that switching from uni- to bidirectional tasks, no matter how low and brief L exertion was in the opposite direction, was associated with an abrupt decrease in G – L coordination. This coordination remained unaffected by the manipulation of external support. The first result corroborates our previous conclusion that the force coordination in uni- and bidirectional manipulation tasks could be based on partly different neural control mechanisms. However, the second finding suggests that the studied control mechanisms could depend more on the cutaneous afferent input, rather than on the synergy of the muscles exerting G and L . more...

In this study we examined an influence of leg extensor strength qualities on agility performance in a latent space. Male physical education students (N = 168) were tested with three standard agility performance tests (lateral stepping, 20-yard shuttle run, and slalom run). Nine measures of leg extensor strength qualities including explosive strength, elastic strength, and maximal strength, were also assessed. As expected, factor analysis of all tests revealed four relatively independent factors: explosive strength, elastic strength, agility, and maximal strength. All three extracted strength factors were included into a regression analysis as predictors to evaluate their influence of the agility factor (i.e. criterion). Although the regression analysis revealed significant multiple correlation between predictors and the criterion (R = 0.41; p0.001), the amount of explained variance of agility performance by the strength factors was rather low (17%). We conclude that the leg extensor strength qualities are poor predictors of agility performance in physically active men. more...

We tested the hypothesis that the performance of rapid movements represents body size-independent indices of muscle power. Physical education students (n¼ 159) were tested on various vertical jump (jump height and average power calculated from the ground reaction force) and muscle strength tests. When non-normalized data were used, a principal components analysis revealed a complex and inconsistent structure where jump height and muscle power loaded different components, while muscle strength and power partially overlapped. When the indices of muscle strength and power were properly normalized for body size, a simple and consistent structure of principal components supported the hypothesis. Specifically, the recorded height and muscle power calculated from the same jumps loaded the same components, separately for the jumps predominantly based on concentric actions and jumps based on a rapid stretch – shortening cycle of the leg extensors. The finding that the performance of rapid movements assesses the same physical ability as properly normalized tests of muscle power could be important for designing and interpreting the results of batteries of physical performance tests, as well as for understanding some basic principles of human movement performance. more...

There is a lack of standardized methodology for normalizing various indices of muscle strength and movement performance tests for differences in body size in human movement-related disciplines. Most of the data presented in the literature have been body size dependent, which precludes both comparisons between subjects and establishment of standards for specific subject populations. The goal of the present review was to propose standardized tests that normalize physical performance tests to body size. Specifically, we propose (a) using an allometric normalization based on theoretical models that presume geometric similarity, (b) using classification of performance tests based on particular values of the allometric parameters required for normalization, and (c) using a simple "performance index" that represents an individual or group performance relative to a reference population. Correspondences between theory and experimental findings and limitations are discussed. more...

The purpose of this study was to compare the effects of sprint and plyometric training on morphological characteristics of physically active men. One hundred and fifty one physical education students (18-24 years of age) were allocated into one of three groups: the plyometric group (PG; n = 50), the sprint group (SG; n = 50), and the control group (CG; n = 51). Both experimental groups participated in a training programme 3 times a week for 10 weeks. SG performed maximal sprints for distances between 10 and 50 meters, while the training programme in PG consisted of hurdle jumps and drop jumps. Anthropometric measurement was performed in the week before and the week after the experiment. There were no significant differences (P > 0.05) in magnitude of changes in any of the analysed anthropometric variables between the groups. However, a significant decrease (P < 0.0167) in the percentage of body fat (6.1%) was found in SG. We also found a significant decrease (P < 0.0167) in body mass (1%), fat-free mass (0.4%) and body mass index (0.9%) for the SG, but the magnitude of these changes was rather low. We conclude that the short-term explosive-type training programmes in which muscles operate in the fast stretch-shortening cycle conditions (i.e., sprinting, jumping) have a limited potential to induce morphological changes in physically active men., Uvod Tijekom posljednjih desetljeća znatan napor trenera i istraživača bio je usmjeren na utvrđivanje optimalnih metoda treninga namijenjenih razvoju jakosti, snage te natjecateljskih kvaliteta. Trenutno se u te svrhe najčešće koriste: 1) trening s velikim opterećenjima (75-90% od maksimalnoga), 2) trening s malim i umjerenim opterećenjima (30-60% od maksimalnoga) eksplozivnoga karaktera i 3) pliometrijski trening. Ovamo svakako ubrajamo i sprinterski trening, no ta metoda nije bila predmetom proučavanja dosadašnjih istraživanja. Prijašnja istraživanja jasno su pokazala kako trening s velikim opterećenjima dovodi do poboljšanja jakosti, snage i motoričke učinkovitosti putem živčano-mišićnih i morfoloških promjena, dok trening s manjim opterećenjem eksplozivnoga karaktera prvenstveno rezultira živčano-mišićnim adaptacijskim promjenama. Učinci sprinterskoga i pliometrijskog treninga na morfološke karakteristike vježbača malo su poznati. Stoga je temeljni cilj ovog istraživanja analizirati efekte sprinterskog i pliometrijskog treninga na morfološke karakteristike mladih i tjelesno aktivnih muškaraca. Metode Ukupno 151 student prve godine Kineziološkog fakulteta dobrovoljno je sudjelovao u ovom istraživanju. Uzorak je abecednim redoslijedom podije-ljen u tri skupine: pliometrijska skupina (PG; n = 50), sprinterska skupina (SG; n = 50) i kontrolna skupina (CG; n = 51). Nije bilo statistički značajnih razlika između grupa na početku eksperimenta ni u jednoj mjerenoj morfološkoj varijabli. Sve tri sku-pine pohađale su redovnu nastavu na prvoj godini studija Kineziološkog fakulteta u trajanju od jednog semestra. Osim toga, grupe PG i SG sudjelovale su u desetotjednom treningu tri puta tjedno po 60 minuta. Grupa PG provodila je pliometrijski trening - skokovi preko prepona i dubinski skokovi, dok je grupa SG provodila sprinterski trening na dionicama između 10m i 50m. Obje su eksperimentalne skupine na svakom treningu izvodile vježbe maksimalnim intenzitetom. Između petog i šestog eksperimentalnog tjedna napravljena je stanka u treningu u trajanju od tjedan dana radi odmora i oporavka vježbača. Educirani mjeritelji obavili su antropometrijska mjerenja tjedan dana prije početka i tjedan dana nakon završetka 10-tjednog eksperimenta u skladu s uputama Međunarodnog biološkog programa (IBP). Mjereneni su: tjelesna masa, tjelesna visina, opseg natkoljenice, opseg potkoljenice te kožni nabori natkoljenice, potkoljenice, prsa, nadlaktice i leđa. Također su izračunati postotak tjelesne masti (Jackson & Pollock; Siri, 1956), nemasna masa tijela te indeks tjelesne mase. Opsezi natkoljenice i potkoljenice korigirani su za veličinu kožnih nabora prema metodi Stewarta i suradnika (2002). Veličine promjena u analiziranim morfološkim varijablama između skupina komparirane su analizom varijance (ANOVA) na varijablama razlika (rezultat finalnog mjerenja minus rezultat inicijalnog mjerenja). Razina statističke značajnosti zaključivanja postavljena je na p < 0.05. Efekti treninga unutar svake skupine analizirani su t-testom za zavisne uzorke s korekcijom razine statističke značajnosti Bonferroni (p < 0.0167). Rezultati Nije bilo statistički značajnih razlika (p > 0.05) između skupina u veličini promjena ni u jednoj morfološkoj varijabli. Trening sprinta doveo je do statistički značajnog (p < 0.0167) smanjenja tjelesne mase (1%), indeksa tjelesne mase (0.9%), nemasne mase tijela (0.4%) te potkožnog masnog tkiva (6.1%). Nije bilo statistički značajnih promjena (p > 0.0167) u analiziranim morfološkim varijablama u skupinama PG i CG. Valja, međutim, istaknuti kako je veličina promjena u varijablama veličine tijela (tj. tjelesna masa, nemasna masa tijela te indeks tjelesne mase) generirana sprinterskim treningom relativno mala (0.4-1%). Rasprava i zaključci Sveukupno gledajući, rezultati ovog istraživanja pokazuju kako i sprinterski i pliometrijski trening u trajanju od 10 tjedana relativno malo utječu na morfološke karakteristike tjelesno aktivnih muškaraca. Naime, nisu utvrđene značajne razlike između eksperimentalnih skupina i kontrolne skupine u veličini promjena analiziranih morfoloških varijabla. Razlog tomu vjerojatno je relativno kratko trajanje eksperimenta (10 tjedana) te homogenost i pozitivna selekcioniranost uzorka ispitanika u području morfoloških obilježja. Ipak, zabilježene su promjene u određenim morfološkim karakteristikama, osobito u skupini SG. Važan i nadasve iznenađujući rezultat ovog istraživanja vezan je uz značajno smanjenje postotka tjelesne masti zabilježen u skupini SG. To je tim više iznenađujuće ako se uzme u obzir da su analizirani ispitanici već na početku eksperimenta imali vrlo nizak postotak tjelesne masti (< 8%). Trend smanjenja postotka tjelesne masti zabilježen je i u skupini PG. Smatramo kako je smanjenje postotka tjelesne masti rezultat prvenstveno povećanja energetske potrošnje koje ispitanici nisu popratili povećanim energetskim unosom. Ukratko, zaključak istraživanja jest kako sprinterski i pliometrijski trening u trajanju od 10 tjedana ograničeno utječu na morfološke karakteristike tjelesno aktivnih muškaraca., Das Ziel dieser Studie war, die Effekte des Sprinttrainings und des plyometrischen Trainings auf die morphologischen Charakteristiken der regelmäßig sporttreibenden Studenten zu bestimmen. Einhundert einundfünfzig Studenten der Kinesiologie (im Alter 18-24 Jahre) wurden einer der drei Gruppen zugeteilt: der plyometrischen Gruppe (PG; n = 50), der Sprint- (SG; n = 50), und der Kontrollgruppe (CG; n = 51). Die beiden experimentellen Gruppen trainierten 10 Wochen, 3 Mal wöchentlich. Die SG legte die Strecken zwischen 10 und 50m in maximalen Sprintläufen zurück, während das Trainingsprogramm für die PG aus Hoch- und Fallsprüngen bestand. Die anthropometrischen Messungen wurden eine Woche vor und eine nach dem Experiment vorgenommen. Keine signifikante Unterschiede (P > 0,05) im Veränderungsumfang aller analysierten anthropometrischen Variablen wurden zwischen den Gruppen festgestellt. Allerdings wurde eine signifikante Abnahme (P < 0,0167) des prozentualen Körperfettanteils (6,1%) in der SG gefunden. Wir bemerkten auch eine signifikante Abnahme (P < 0,0167) in der Körpermasse (1%), der fettfreien Masse (0,4%) und im Köpermassenindex (0,9%) bei der SG, aber das Ausmaß dieser Veränderungen war ziemlich niedrig. Wir schließen daraus, dass die kurzfristige und explosive Übungen beinhaltenden Trainingsprogramme, bei denen die Muskel in den Umständen des schnellen Dehnungs-Verkürzungs-Zyklus arbeiten (z.B. Sprintläufe, plyometrische Sprünge) einen begrenzten Potential besitzen, um morphologische Veränderungen bei den regelmäßig sporttreibenden Männern beizubringen. more...

The primary aim of this study was to determine reliability and factorial validity of squat (SJ) and countermovement jump (CMJ) tests. The secondary aim was to compare 3 popular methods for the estimation of vertical jumping height. Physical education students (n = 93) performed 7 explosive power tests: 5 different vertical jumps (Sargent jump, Abalakow's jump with arm swing and without arm swing, SJ, and CMJ) and 2 horizontal jumps (standing long jump and standing triple jump). The greatest reliability among all jumping tests (Cronbach's alpha = 0.97 and 0.98) had SJ and CMJ. The reliability alpha coefficients for other jumps were also high and varied between 0.93 and 0.96. Within- subject variation (CV) in jumping tests ranged between 2.4 and 4.6%, the values being lowest in both horizontal jumps and CMJ. Factor analysis resulted in the extraction of only 1 significant principal component, which explained 66.43% of the variance of all 7 jumping tests. Since all jumping tests had high correlation coefficients with the principal component (r = 0.76- 0.87), it was interpreted as the explosive power factor. The CMJ test showed the highest relationship with the explosive power factor (r = 0.87), that is, the greatest factorial validity. Other jumping tests had lower but relatively homogeneous correlation with the explosive power factor extracted. Based on the results of this study, it can be concluded that CMJ and SJ, measured by means of contact mat and digital timer, are the most reliable and valid field tests for the estimation of explosive power of the lower limbs in physically active men. more...

Background Delayed onset muscle soreness, induced by strenuous exercise, is one of the most common recurrent forms of sports injury and is associated with exercise-induced muscle damage (EIMD). Objective We examined the effects of whole-body cryotherapy (WBC) on biochemical markers, pain, and performance parameters during a 5-day recovery period after a damaging plyometric exercise. We hypothesized that WBC would have beneficial effects on muscle recovery after such an exercise bout. Design Randomized crossover study design. Setting Recreational athletes. Participants 11 recreational male athletes volunteered in this study. Inclusion criteria were that the subjects were familiar with plyometric exercise, but they did not perform this type of exercise for at least 3 months prior to the study, were not injured or receiving any medications in the last 9 months, and were within normal baseline levels for biochemical markers. Interventions Participants completed a bout of damaging exercise for the hamstring muscles on two separate occasions separated by 10 weeks. During the control condition, subjects received no treatment after the damaging exercise. The experimental condition consisted of WBC everyday during the recovery period. WBC included single 3-min daily exposures to low temperatures (–140 to –195 °C) in the cryo-cabin. Main outcome measurements Biochemical markers, perceived pain sensation, squat- and counter movement-jump, maximal and explosive isometric torque production. Results Majority of the observed variables showed statistically significant time effects (P Conclusions The results of the present study do not provide conclusive support for the use of WBC as a technique to enhance functional recovery after EIMD. more...

This paper deals with functional organisation of a call centre by adjusting the amount of human and technical resources such that the quality of service is satisfied while the costs of the resources are significantly reduced. If the call centre is not well designed, a great number of repeated requests occur, particularly in periods of peak traffic intensity. In such circumstances, the recorded data statistics give an unreal number of callers. This paper proposes a new method for estimating the real number of callers and the offered traffic using the general probability theory. Additionally we developed the two-level dynamic programming (DP) method for call centre staffing optimisation. Proposed method enables optimal allocation of available human resources by shifts such that the operation costs are significantly reduced. more...