Trunk muscle activation patterns in subjects with low back pain

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The research of combustion process of diesel engine using biofuels and exhaust gas recirculation

U ovom radu je proucavana mogucnost primene alternativnih biogoriva za pogon dizel motora sa direktnim ubrizgavanjem, kao i uticaj ovih goriva na proces sagorevanja i izduvnu emisiju ovog tipa motora. Kao alternativna biogoriva korišceni su metilestri ulja uljane repice, sojinog ulja i otpadnog jestivog palminog ulja. Ova biogoriva su korišcena kao cista (100%) ili u smeši sa standardnim dizel gorivom fosilnog porekla u odnosu 50:50 i u nekim uslovima i u smeši 25%, 50%, 75%. Takode, istražena je i mogucnost primene cistog jestivog rafinisanog suncokretovog ulja bez dodatne obrade ulja pre mešanja sa dizel gorivom u odnosu 50:50. Pored integralnih karakteristika motora: snage, obrtnog momenta, potrošnje usisnog vazduha i goriva, analize izduvnih gasova, protoka recirkulacije izduvnih gasova, snimljeni su tokovi pritiska u cilindru motora i vodu visokog pritiska sistema unrizgavanja i izdizanje igle brizgaca, korišcenjem akvizicionog sistema visokih performansi. Na bazi ovih velicina razvijen je i primenjen model za odredivanje parametara procesa sagorevanja. Koristeci ovaj postupak odredene su sledece karakteristike sagorevanja pri radu sa razlicitim biogorivima i pri razlicitim uslovima: vrednosti maksimalnog pritiska u cilindru motora kao i njihovi položaji u odnosu na SMT, zakoni oslobadanja toplote, periodi zakašnjenja upaljenja, trajanje sagorevanja i razvijene kolicine energije po fazama procesa sagorevanja. Takode je izvršeno ispitivanje uticaja svih korišcenih biogoriva na izduvnu emisiju motora. Istraživanja su vršena u usisnoj i natpunjenoj varijanti motora. Takode je detaljno istražen i uticaj recirkulacije izduvnih gasova na proces sagorevanja i izduvnu emisiju i to u obe varijante motora i sa svim korišcenim biogorivima. Poseban deo istraživanja se odnosio na mogucnost aplikacije komore za sagorevanje originalne konstrukcije sa smanjenim odavanjem toplote i uticaj ovog sistema sagorevanja na tok procesa sagorevanja i sastav izduvnih gasova. Dobijeni rezultati u okviru ovog rada se mogu koristiti pri optimizaciji radnog ciklusa dizel motora sa direktnim ubrizgavanjem u cilju postizanja povoljnije ekonomicnosti i izduvne emisije, pri pogonu biogorivima sa i bez recirkulacije izduvnih gasova.This dissertation presents the results of biofuels application research in direct injection diesel engine, as well as the influence of these fuels on engine combustion process and exhaust emissions. The methyl esters of rape oil, soya oil, and waste cooking palm oil were used as alternative fuels. These biofuels were used as net fuels (100%) as well as mixed with standard diesel fuel in the ratio 50:50 and in several cases 7%, 25%, 50% and 75%. Also, the research included the experiments with pure edible sunflower oil mixed with diesel fuel in the ratio 50:50. Besides engine integral characteristic: power and torque output, intake air and fuel consumption, exhaust gas analysis, exhaust gases recirculation, the traces of incylinder pressure, fuel injection pressure and injector needle lift were recorded using high speed data acquisition system. On the basis of these data the method of combustion process parameters evaluation was developed and applied. Using this procedure for different biofuels and at different operating conditions, the following combustion parameters were determined: maximum cylinder pressure and temperature and its their position relative to TDC, heat release and the rate of heat release, ignition delay, combustion duration and the amount of heat released in certain periods of combustion process. The research was carried out under the naturally aspirated and supercharged engine conditions. The impact of exhaust gas recirculation on combustion process and exhaust emissions was studied in all operating conditions and with all biofuels. A special part of the research related to the possibilities of application of the specially designed combustion chamber with reduced heat transfer from the gases to the chamber walls. The influence of this system on combustion characteristics and exhaust emissions was studied. The results obtained in this research can be used for optimisation of diesel engine working cycle in order to achieve better fuel economy and exhaust emissions, under the conditions of different biofuels application with and without exhaust gas recirculation

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

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

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

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

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

Reliability of Sprint Force-Velocity-Power Profiles Obtained with KiSprint System

This study aimed to assess the within-and between-session reliability of the KiSprint system for determining force-velocity-power (FVP) profiling during sprint running. Thirty (23 males, 7 females; 18.7 ± 2.6 years;) young high-level sprinters performed maximal effort sprints in two sessions separated by one week. Split times (5, 10, 20 and 30 m), which were recorded with a laser distance meter (a component of the KiSprint system), were used to determine the horizontal FVP profile using the Samozino’s field-based method. This method assesses the FVP relationships through estimates of the step-averaged ground reaction forces in sagittal plane during sprint acceleration using only anthropomet-ric and spatiotemporal (split times) data. We also calculated the maximal theoretical power, force and velocity capabilities and the slope of the FV relationship, the maximal ratio of horizontal-to-resultant force (RF), and the decrease in the RF (DRF). Overall, the results showed moderate or good to excellent within-and be-tween-session reliability for all variables (ICC > 0.75; CV < 10 %), with the exception of FV slope and DRF that showed low rel-ative reliability (ICC = 0.47-0.48 within session, 0.31-0.33 be-tween-session) and unacceptable between-session absolute reliability values (CV = 10.9-11.1 %). Future studies are needed to optimize the protocol in order to maximize the reliability of the FVP variables, especially when practitioners are interested in the FV slope and DRF. In summary, our results question the utility of the sprint-based FVP profiling for individualized training pre-scription, since the reliability of the FV slope and D RF variables is highly questionable

Effects of Resistance Training With Constant, Inertial, and Combined Loads on Muscle Power and Strength Output

The aim of this study was to investigate the resistance-specific gains in muscle power and strength (1RM) following the training of maximum bench-press throws (BPT) against constant, inertial, and combined resistance. Forty-eight male participants (age 20.5 ± 2.0 years) were randomly assigned to the constant, inertial, combined resistance, or control group. Participants underwent 8 weeks of training of BPT against the loads that corresponded to the different effects of mass of 40 kg (∼50% of 1RM). The gains in average and maximum power, and 1RM were significant in all experimental groups (P 0.1). Relative gains in the average (26.3 ± 9.8%) and maximum power (25.2 ± 9.8%) were larger than that in the 1RM (mean 7.2 ± 6.9%; both P < 0.001). The gains in the average (F4, 66 = 6.0; P < 0.01) and maximum power (F4, 66 = 4.7; P < 0.01) were higher when tested against the training-specific resistance than when tested against the remaining two resistance types. Differences in 1RM among experimental groups were not significant (P = 0.092). The most important and rather novel finding of the study is that the training against the weight and inertial resistance, and their combination results in resistance-specific gains in muscle power, although the overall gains muscle strength and power remain comparable across the training protocols