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The increase in tissue extensibility and joint range of motion through stretching has often been demonstrated. However, the existence of an optimal stretch duration has not been proven and the identification of an ideal number of repetitions of a stretch has received little attention in the literature. The purpose of this study was to examine and clarify the relationship of duration and number of repetitions of a stretch and their effect on changes in hamstring extensibility (HE) resulting from a stretching program. The HE of 33 subjects who were randomly assigned to a control group or one of three treatment groups was assessed before and after a three-week stretching program. The subjects in the three treatment groups stretched once a day, five times a week, and either once for 15 seconds (1 X 15), twice for 15 seconds (2 X 15), or once for 30 seconds (1 X 30). A repeated measures ANOVA showed no statistically significant effect for treatment group (P=0.181) or for treatment by pre- and post-treatment measurements (P=0.140), but indicated a significant difference between pre- and post-treatment measurements (P<0.001). The HE of the control group (which did not stretch) changed only slightly (0.9��, SD 5.7), the 1 X 15 and 1 X 30 groups improved more clearly (4.2��, SD 3.1 and 3.8��, SD 6.7, respectively), and the 2 X 15 group's HE increased the most (6.8��, SD 3.9). The results suggest that varying durations and repetitions of a stretch may influence the magnitude of improvement of HE. However, with the relatively low power (0.46) in the present study, no statistically significant difference between stretching protocols of 1 X 15 seconds, 2 X 15 seconds, and 1 X 30 seconds could be found. / Graduation date: 1997

Although traditional prevention and management strategies for hamstring injuries have focussed on optimising muscle strength, flexibility and endurance, incidence and/or recurrence rates of these injuries remains high. A theoretical framework was developed considering additional factors that increase the stabilising demand of the hamstrings. These factors included loss of related stability at the knee and lumbopelvic regions and extrinsic factors during functional and sporting activities. The aims of this research were to determine whether electromyographic (EMG) derived hamstrings, quadriceps and gluteal muscle activation patterns as well as isokinetic torque generation patterns could differentiate athletes who had incurred a hamstring injury from uninjured control athletes. It was hypothesised that the EMG activity of the injured participants would be decreased compared to uninjured control participants during maximal activities, but increased during weight bearing activities. The research included the identification of laboratory-based tasks relevant to the function of the hamstring muscles; test-retest reliability of EMG variables recorded during these tasks; and a comparative cross-sectional study of hamstring-injured (hamstring group, HG) and control athletes (control group, CG). Electromyographic activation patterns were determined during assessment of concentric and eccentric isokinetic strength of the thigh muscles, during transition from double- to single-leg stance, and forward lunging. Isokinetic and EMG onset and amplitude variables were compared both within- and between-groups. Despite no significant differences for peak torque, the HG injured limb generated lower average eccentric flexor torque towards the outer range of motion in comparison to the HG uninjured limb (P = 0.034) and the CG bilateral average (P = 0.025). Furthermore, the EMG root mean square (RMS) decrease from the start to the end range of the eccentric flexor contraction was greater for the HG injured limb hamstrings than the CG bilateral average. During the transition from double- to single-leg stance, the EMG onsets of the HG injured limb (biceps femoris [BF] P < 0.001, medial hamstrings [MH] P = 0.001), and the HG uninjured limb (BF P = 0.023, MH P = 0.011) were earlier in comparison to the CG bilateral average. The transition normalised EMG RMS was significantly higher for the HG injured side BF (P = 0.032), MH (P = 0.039) and vastus lateralis (VL, P = 0.037) in comparison to the CG bilateral average. During the forward lunge, no significant differences were observed within- and between-groups for the normalised EMG amplitude prior to and following initial foot contact. These results suggest that during maximal isokinetic eccentric flexor contractions, the average torque and EMG activity is decreased towards the lengthened position of the hamstring-injured limb. This may be due to structural changes or neurophysiological inhibitory mechanisms. During the static weight bearing task an earlier onset of the HG hamstring muscles was evident in comparison to controls. The hamstrings and the VL of the injured limbs were activated at greater normalised amplitude. The increased muscle activation in the hamstring-injured limbs during the support phase may indicate a greater demand towards stability of the kinetic chain or changes in proprioceptive function. Future research should consider the mechanisms and clinical implications underlying a loss of eccentric flexor torque towards the outer range of contraction, and investigate why increased activation of thigh muscles occurs during the static weight bearing task in hamstring-injured athletes.

<p>Bol je subjektivno, neprijatno opažanje i osećaj. Čovek često oseća bol u delu tela koji<br />je znatno udaljen od mesta nastanka bola. U istraživanju je primenjena transverzalna<br />metoda, jednokratnog merenja. Ispitivanjem je obuhvaćeno 136 ispitanika, aktivnih<br />fudbalera, starosti 18-35 (20.49&plusmn;3.73) godina. Sva merenja su vr&scaron;ena od 2006. do<br />2016.godine. Ispitanici su ispunili anketu o postojanju bola u leđima, pre samog<br />početka testiranja, gde su intenzitet bolnosti subjektivno procenili Rolandovom skalom<br />bola). Celokupan uzorak je stratifikovan proporcionalnom tehnikom u pet grupa na<br />osnovu subjektivnog osećaja bola u leđima. Multivarijantnom metodom varijanse<br />utvrđivane su razlike na generalnom sistemu uzorkovanih varijabli, prilikom čega je<br />ustanovljeno da postoji statistički značajna razlika između navedenih grupa ispitanika<br />podeljenih na osnovu subjektivnog osećaja bola u leđima u izokinetičkim varijablama<br />koje su uzete u obzir ovim istraživanjem dok su Univarijantnom analizom varijanse<br />utvrđene razlike u pojedinačnim varijablama. Iz navedenih empirijskih saznanja i<br />relevantnih podataka iz stručne literature dobija se uvid u faktore koji utiču na bolno<br />stanje određene regije, disfunkciju i slabost pojedinih mi&scaron;ićnih grupa, uticaj pojedinih<br />mi&scaron;ićnih grupa na druge, kao i poremećaj u kinetičkom lancu lokomotornog aparata<br />kod fudbalera. Samo istraživanje ukazuju na značaj i potrebu da se standardizuju<br />protokoli i konstrui&scaron;u odgovarajući algoritmi za komparativnu sistematizaciju varijabli<br />dobijenih specifičnim ispitivanjima izokinetičkom dinamometrijom kod ispitanika koji<br />se bave timskim sportom sa loptom (fudbal, kosarka, rukomet i dr). Dobijeni podaci<br />poslužiće jednim delom kao deo monitoringa sportskog treninga, kao i efekata<br />različitih trenažnih protokola na parametre mi&scaron;ićne snage kod fudbalera. Sportskomedicinski značaj na polju testiranja parametara mi&scaron;ićne snage izokinetičkom<br />dinamometrijom se ogleda u prevenciji sportskih povreda ili u brzoj i efikasnoj<br />dijagnostici i terapiji istih, &scaron;to značajno utiče na ekonomski aspekt, s obzirom da je<br />profesionalni sport postao visoko komercijalizovan.</p> / <p>Pain is a subjective, uncomfortable perception and feeling. Human often feels<br />pain in the part of the body that is significantly away from the place of origin of pain.<br />The transversal method was performed during study, with a one-time measurement.<br />The study included 136 subjects, active players, ages 18-35 (20:49 &plusmn; 3.73) years. All<br />measurements were carried out from 2006 to 2016. Before the start of the test,<br />examinee completed the survey on the existence of back pain, where the intensity of<br />the pain was subjectively assessed according to Roland pain scale. The entire sample was stratified by proportional technique into five groups, based on the subjective experience of back pain. Multivariate variance method for detection of differences in the general system of sampled variables, during which it was established that there is a statistically significant difference between the groups of examinee, who were divided on the basis of subjective experience of back pain of the isokinetic variables that are taken into account in this study while the univariate analysis of variance determined differences in the individual variables. From the empirical findings above and relevant information from technical literature, an insight was obtained into the factors that influence the painful condition of a particular region, dysfunction and weakness of certain muscle groups, the impact of certain muscle groups on others, as well as the disruption in the kinetic chain of the locomotor apparatus. The research highlights the importance of and the need to standardize protocols and construct appropriate algorithms for comparative systematization of variables obtained by isokinetic dynamometry specific trials in subjects who are engaged in team sports with a ball (football, basketball, handball, etc.). The data will serve partially as part of the monitoring of sports training, as well as the effects of various parameters of training protocols on muscle strength in football. Sports and medical significance in the field of testing parameters with isokinetic muscle strength dynamometry is reflected in the prevention of sports injuries or in the quick and efficient diagnosis and treatment of the same, which significantly affects the economic aspect, considering that professional sport has become highly commercialized.</p>

La compréhension du comportement musculaire est un champ d’investigation primordial dans divers domaines tels que le sport, le crash automobile et la médecine. Peu de techniques in vivo permettent aujourd’hui de caractériser les propriétés mécaniques du muscle. Aussi, l’objectif de ce travail est de développer une méthode d’identification in vivo à partir demesures de champs de déplacement. La méthode d’identification est composée de 3 étapes interdépendantes. La première consiste à réaliser une IRM de la cuisse pour segmenter manuellement différents tissus musculaires (quadriceps, ischios, gracilis et sartorius) et le tissu adipeux. Un comportement Néo-Hookéen est choisi pour modéliser le comportement hyperélastique (C10, D). Dans un second temps, un dispositif expérimental de compression est développé pour mesurer le champ de déplacement in vivo à partir des techniques d’imagerie échographique et de Corrélation d’Images Numériques. Finalement, une méthode inverse est mise en œuvre pour identifier les paramètres C10 et D de chaque tissu. Par le biais d’un exemple numérique, l’erreur sur les paramètres identifiés est évaluée. Les cartographies des champs de déplacement expérimentaux confirment les observations qualitatives obtenues sur les images échographiques et sont validées par les champs de déformation obtenus par approximation diffuse. Une faible erreur d’identification (C10<3%, D<7%) est obtenue à partir de l’exemple numérique, et les paramètres mécaniques identifiés sont en accord avec la littérature. Ces résultats valident la démarche inverse mise en œuvre qui permettra, à terme, de suivre l’évolution des pathologies et de mener des simulations prédictives. / The understanding of the mechanical behavior of the muscle tissue is an important field of investigation with different applications in medicine, car crash and sport. Currently, few in vivo imaging techniques are able to characterize the mechanical properties of muscle. Thus, this study aims at developing an in vivo identification method based on displacement fieldmeasurements. The identification approach is composed of 3 dependent steps. The first step consists in performing a 2D MRI acquisition of the thigh in order to segment manually the muscle (quadriceps, ischio, gracilis and sartorius) and fat tissues. A Neo-Hookean model is chosen to characterize the hyperelastic behavior (C10, D). Secondly, an experimental compressiondevice is developed to measure the in vivo displacement field using ultrasound and Digital Image Correlation (DIC) techniques. Finally, an inverse method is implemented to identify the C10 and D parameters of each soft tissue. A numerical example is used to quantify the identification error on each parameter. Displacement field measurements confirm the ultrasound observations. They are also validated by the cartographies of the strain fields, which are obtained by the diffuse approximation method. Using the numerical example, the identification leads to low errors on the C10 (< 3%) and D (< 7%) parameters. Identified values of the mechanical parameters are in good agreement with the literature. All results validate the implemented identification method. In the long term, this protocol will allow to follow the evolution of pathologies and to conduct predictive simulations.