Trunk muscle activation patterns in subjects with low back pain

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Uloga izostajanja sa nastave u predviđanju matematičkog postignuća na osnovu self-koncepta i motivacije - TIMMS 2015 u Srbiji

This study examines how students' absenteeism moderates the relationship of math Self-Concept and motivation to learn math on one side and the achievement in the TIMSS 2015 math test on the other. The stratified random sample consists of 4036 fourth grade pupils from 160 primary schools in Serbia. Separate regression models were made for four levels of frequency of students' absenteeism. The results show that Self-Concept makes a positive contribution to the prediction of achievement, and motivation a negative one. Additionally, with the increase of absenteeism the importance of Self-Concept drops and that of motivation grows. The analysis of variance confirmed that along with the increase of absenteeism, students express lower levels of Self-Concept, while the level of motivation does not change. The most important conclusion is that regular class attendance contributes to the students' math Self-Concept and consequential achievement by developing their experiences of success in math. The usefulness of the motivation scale for predicting math test performance is discussed.U ovom istraživanju je ispitivano kako izostajanje učenika sa nastave moderira povezanost matematičkog self-koncepta i motivacije za učenje matematike sa jedne strane i postignuća na TIMSS 2015 testu iz matematike sa druge. Stratifikovani slučajni uzorak se sastojao od 4036 učenika četvrtog razreda iz 160 osnovnih škola u Srbiji. Posebni regresioni modeli su sastavljeni za svaki od četiri nivoa učestalosti izostajanja učenika sa nastave. Rezultati su pokazali da self-koncept ima pozitivan doprinos predikciji postignuća, dok je doprinos motivacije negativan. Pored toga, sa porastom izostajanja važnost self-koncepta opada, a motivacije raste. Analiza varijanse je potvrdila da sa porastom izostajanja učenici pokazuju niži nivo self-koncepta, dok se nivo motivacije ne menja. Najvažniji zaključak je da redovno pohađanje nastave doprinosi matematičkom self-konceptu učenika i posledičnom postignuću tako što podstiče njihovo iskustvo uspeha u matematici. Diskutovana je korisnost skale motivacije za predviđanje postignuća na testu iz matematike

ASSESSMENT OF THIGH MUSCLES MECHANICAL CAPACITIES FOLLOWING ACL RECONSTRUCTION USING THE TWO-VELOCITY METHOD

We evaluated the ability of recently proposed two-velocity method to discriminate between thigh muscle mechanical capacities of the involved and the uninvolved leg following ACL reconstruction (ACLR). 15 athletes were tested 4 and 6 months following ACLR. F-V linear relationship parameters (F intercept - F0, V intercept - V0, slope – a, and Pmax) were obtained from line drawn through 60 and 180 °/s data (the \u27two-velocity method\u27). In quadriceps, all parameters revealed between leg differences 4 and 6 months after ACLR. In addition F0 and V0 of the involved leg were higher at 6 than at 4 months after ACLR. In hamstrings, differences between legs were found only for F0 at 4 months. In conclusion, parameter of the two-velocity method could be sensitive enough to detect between-leg differences in muscle F, V, and P producing capacities following ACLR

Interlimb Asymmetries and Ipsilateral Associations of Plantar Flexors and Knee Extensors Rate-of-Force Development Scaling Factor

Rate of force/torque development scaling factor (RFD-SF/RTD-SF) was recently introduced as a tool to quantify the neuromuscular quickness, and it could have potential for interlimb asymmetry identification. Moreover, positive relationships in RFD-SF ability among different muscle groups were shown, but not in the lower extremity. The first aim of our study was to use RTD-SF for interlimb asymmetry identification. The second aim was to determine associations between plantar flexors (PF) and knee extensors (KE). Forty young healthy athletes (14.8 +/- 1.2 years) performed explosive isometric contractions to a span of torque levels for PF and KE. From rapid isometric contractions, the RTD-SF and linearity (r(2)) of the regression line were calculated. Using RTD-SF we identified 10% (PF) and 15% (KE) of subjects with contralateral asymmetries ( gt 15% criterion). The results revealed significant positive moderate correlation in RTD-SF between PF and KE (r = 0.401, p lt 0.05). We supported that RTD-SF can be a useful tool for interlimb asymmetry identification. Future research about observed asymmetry in rapid submaximal contractions deserves more attention, as most of the functional sport specific activities put high demands on rapid force production. Our study as first confirmed positive associations in RTD-SF ability between muscle groups in lower limbs

Control Strategy of Maximum Vertical Jumps: the Preferred Countermovement Depth May Not Be Fully Optimized for Jump Height

The aim of the present study was to explore the control strategy of maximum countermovement jumps regarding the preferred countermovement depth preceding the concentric jump phase. Elite basketball players and physically active non-athletes were tested on the jumps performed with and without an arm swing, while the countermovement depth was varied within the interval of almost similar to 30 cm around its preferred value. The results consistently revealed 5.1-11.2 cm smaller countermovement depth than the optimum one, but the same difference was more prominent in non-athletes. In addition, although the same differences revealed a marked effect on the recorded force and power output, they reduced jump height for only 0.1-1.2 cm. Therefore, the studied control strategy may not be based solely on the countermovement depth that maximizes jump height. In addition, the comparison of the two groups does not support the concept of a dual-task strategy based on the trade-off between maximizing jump height and minimizing the jumping quickness that should be more prominent in the athletes that routinely need to jump quickly. Further research could explore whether the observed phenomenon is based on other optimization principles, such as the minimization of effort and energy expenditure. Nevertheless, future routine testing procedures should take into account that the control strategy of maximum countermovement jumps is not fully based on maximizing the jump height, while the countermovement depth markedly confound the relationship between the jump height and the assessed force and power output of leg muscles

RELIABILITY AND GENERALIZABILITY OF CONSECUTIVE MAXIMUM CONTRACTIONS AS A TEST OF NEUROMUSCULAR FUNCTION

The aim of the study was to explore the intra- and inter- session reliability, generalizability, as well as the factorial validity of the recently proposed novel test of neuromuscular function. Twelve participants took part in the first experiment, performing the standard strength test (SST) and a novel test based on consecutive maximum contractions (CMC) tests on the knee extensor muscle. Within the second experiment, additional 36 participants performed the SST and CMC tests on the knee and elbow flexor and extensor muscles. The obtained results for the SST and CMC revealed high day by day and test-retest reliability in most measured variables (ICC in the range of 0.80 - 0.92). The principal component analysis (PCA) applied on the SST variables revealed 3 factors that explained 81.2% of the non-normalized and 66.1% of the normalized data. The PCA applied on all 16 non-normalized variables of the CMC test revealed 3 factors that explained 80% of the total variance. Another PCA with the rate of force development and relaxation (RFD and RFR) normalized in regards  to the PF revealed 4 factors that explained 70.9% of the total variance. Non-normalized factors were not loaded with different muscle groups, but with variables of the same muscle group. After the applied normalization, the individual factors were loaded with the variables recorded from individual muscles. The results of the CMC suggest that the ability of the RFD and RFR could be partially independent. The CMC may be a feasible alternative to SST since it could assess the same strength properties from muscles through a single trial, based on a relatively low and transient force

Procjenjivanje jakosti nakon ozljede prednje ukrižene sveze u sportaša

The anterior cruciate ligament injury is one of the most common injuries in athletes. A limited range of motion, abnormal gait mechanics, quadriceps and hamstring muscles strength loss, and very often a decreased return to pre-injury levels of activity are concomitant to ligament reconstruction. Tremendous efforts have been made over the past two decades toward an accelerated rehabilitation in order to minimize the functional and mechanical knee instability as well as quadriceps and hamstring muscles strength loss. Various strength test protocols have been employed to determine the magnitude of reduction in muscle strength, and to provide criteria for an athlete’s progression through the phases of recovery. However, since it is only the open kinetic chain feature that enables specific quantification of strength deficits in isolated muscles, this manuscript will focus on the methods for strength assessment which utilize unilateral OKC movements. By summarizing the principles and methods for strength assessment (isokinetic, isometric and isoinertial), we aimed at providing a comprehensive understanding of the current state of research that could guide the clinicians in conducting reasoned interventions.Ruptura prednjega križnog ligamenta (Anterior Cruciate Ligament – ACL) svrstava se u najčešće i najozbiljnije ozljede u sportu. Ozljedu prate ograničen opseg pokreta, narušen obrazac hoda, slabost opružača i pregibača zgloba koljena i vrlo često nemogućnost povratka na razinu sportske aktivnosti od prije ozljede. Tijekom posljednja dva desetljeća rehabilitacijski protokoli znatno su unaprijeđeni kako bi se ograničila funkcionalna i mehanička nestabilnost koljena i spriječio veći gubitak jakosti opružača i pregibača. Nakon ozljede, primjenjuju se različiti protokoli za procjenu jakosti radi utvrđivanja veličine redukcije mišićne jakosti, ali i za određivanje standarda za napredovanje sportaša kroz faze oporavka. Kako samo testovi koji se izvode u otvorenom kinetičkom lancu dopuštaju kvantifikaciju deficita u mišićnoj jakosti izoliranog mišića, ovaj pregledni članak bavit će se isključivo metodama procjene jakosti koje su zasnovane na unilateralnim pokretima koji se izvode u otvorenom lancu. Cilj je ovog rada bio da se pregledom principa i metoda za procjenu jakosti (izokinetičke, izometrijske i izoinercijske) omogući razumijevanje rezultata novijih istraživanja, koji bi liječnicima mogli pomoći u realizaciji odgovarajućih intervencija

Alternating Consecutive Maximum Contraction as a Test of Muscle Function in Athletes Following ACL Reconstruction

The novel test based on isometric alternating consecutive maximal contractions performed by two antagonistic muscles has been recently proposed as a test of muscle function in healthy subjects. The aim of this study was to evaluate reliability and sensitivity of a novel test as a test of knee muscles function in athletes recovering from anterior cruciate ligament reconstruction. Fifteen male athletes with recent ligament reconstruction (4.0 +/- 0.1 months following the surgery) and 15 sport and physical education students participated in the study. Peak torques of the quadriceps and hamstring muscles assessed both through the alternating consecutive maximal contractions and standard isokinetic test performed at 60 ((degrees) under bar)/s and 180 ((degrees) under bar)/s served for calculation of the hamstrings-to-quadriceps ratio and the bilateral difference in strength. When applied on individuals recovering from anterior cruciate ligament reconstruction, the novel test revealed a high within-day reliability and sensitivity for detecting imbalances both between antagonistic and between contralateral muscles. The present findings suggest that alternating consecutive maximal contractions could be used as a test of muscle function that is either complementary or alternative to the isokinetic test, particularly in the laboratories where the isokinetic devices are not available. Potential advantages of the novel test could be both a brief testing procedure and a possibility to conduct it using relatively inexpensive devices such as custom made kits containing a single one-axis force transducer

Jačine i odnosi jačina mišića ekstenzora i fleksora kolena kod sportista nakon rekonstrukcije prednjeg ukrštenog ligamenta

Introduction Maximal strength ratios such as the limb symmetry index (LSI) and hamstring-to-quadriceps ratio (HQ) may be considered the main outcome measures in the monitoring of recovery after anterior cruciate ligament (ACL) reconstruction. Although explosive strength is much more important than maximal strength, it is generally disregarded in the follow-up of muscle function recovery. Objective The purpose of this study was to compare ratios between maximal (Fmax) and explosive strength (rate of force development - RFD) in individuals with ACL reconstruction. Methods Fifteen male athletes were enrolled and had maximum voluntary isometric quadriceps and hamstring contractions tested (4.0 ± 0.1 months post reconstruction). In addition to Fmax, RFD was estimated (RFDmax as well as RFD at 50, 100, and 200 ms from onset of contraction) and LS gt I and HQ ratios were calculated. Results The involved leg demonstrated significant hamstring and quadriceps deficits compared to uninvolved leg (p lt 0.01). Deficits were particularly significant in the involved quadriceps, causing higher HQ ratios (average 0.63), compared to the uninvolved leg (0.44). LSI was significantly lower for RFD variables (average 55%) than for Fmax (66%). Conclusion The assessment of RFD may be considered an objective recovery parameter for one's readiness to return to sports and should be an integral part of standard follow-up protocol for athletes after ACL reconstruction. Moreover, the combination of indices derived from maximal and explosive strength may provide better insight in muscle strength balance, as well as a clear picture of functional implications.Uvod Maksimalne jačine ekstenzora i fleksora kolena, njihov međusobni odnos (eng. hamstrings-to-quadriceps ratio; HQ), kao i indeks simetrije operisane i neoperisane noge (eng. limb symmetry index; LSI) važni su pokazatelji pomoću kojih se prati oporavak nakon rekonstrukcije LCA. Iako je za izvođenje brojnih funkcionalnih zadataka eksplozivna jačina važnija od maksimalne, ova sposobnost generalno je zanemarena u praćenju oporavka mišićne funkcije. Cilj rada bio je da se uporede odnosi (maksimalne jačine (Fmax) i odnosi eksplozivne jačine (eng. Rate of Force Development - RFD) kod sportista sa rekonstrukcijom LCA. Metode rada U studiju je uključeno 15 sportista, kojima je testirana maksimalna voljna izometrijska kontrakcija (MBK) ekstenzora i fleksora kolena (4,0 ± 0,1 meseca postoperativno). Pored Fmax, procenjivan je i RFD (RFDmax, kao i RFD na 50, 100 i 200 ms od početka kontrakcije) i računati odnosi jačine (LSI i HQ odnos). Rezultati Maksimalna jačina i ekstenzora i fleksora operisane noge bila je značajno niža nego kod neoperisane noge (p lt 0,01). Deficiti su bili posebno izraženi kod ekstenzora operisane noge, usled čega su i HQ odnosi na toj strani (prosečno 0,63) bili veći nego kod neoperisane noge (0,44). Indeks simetrije je bio značajno niži za varijable RFD (prosečno 55%) nego za Fmax (66%). Zaključak Procena eksplozivne jačine može biti još jedan objektivni pokazatelj oporavka i spremnosti za izlaganje specifičnim opterećenjima i kretnjama, zbor čega bi trebalo da bude deo standardnog protokola za praćenje sportista nakon rekonstpukcije LCA. Štaviše, kombinacija indeksa izvedenih iz maksimalne i eksplozivne jačine morala bi dati kompletniji uvid u balans jačine mišića za kretnje koje zahtevaju maksimalne i eksplozivne akcije, kao i jasnu sliku o funkcionalnim implikacijama

Isokinetic Testing: Sensitivity of the Force-Velocity Relationship Assessed through the Two-Point Method to Discriminate between Muscle Groups and Participants' Physical Activity Levels

Background: Isokinetic testing has been routinely used to assess the capacities of individual muscle groups. In this study we aimed to evaluate the sensitivity of the force-point (F-v) relationship assessed through the two-point method to discriminate between antagonist muscle groups and males with different physical activity levels. Methods: The concentric force output of the knee, hip, elbow, and shoulder flexors and extensors of 27 active and 13 non-active men was recorded at 60 and 180 degrees/s to determine the F-v relationship parameters (maximum force [F-0], maximum velocity [v(0)], and maximum power [P-max]). Results: F-0 and P-max were higher for knee extensors (effect size [ES] = 1.97 and 0.57, respectively), hip extensors (ES = 2.52 and 0.77, respectively), and shoulder flexors (ES = 1.67 and 0.83, respectively) compared to their antagonist muscles, while v(0) was higher for knee flexors compared to knee extensors (ES = 0.59). Active males revealed higher F-0 for knee extensors (ES = 0.72) and knee flexors (ES = 0.83) and higher P-max for knee flexors (ES = 0.70), elbow extensors (ES = 0.83) and shoulder extensors (ES = 0.36). Conclusions: The sensitivity of the two-point method for testing the maximal mechanical capacities was high for the knee, moderate for the hip and shoulder, and low for the elbow joint