THE INFLUENCE OF STATIC STRETCHING ON THE VISC0ELASTIC PROPERTIES OF M. TRICEPS SURAE

Though the practice of stretching is widely used in sports, general fitness and physiotherapy, there is still a lack of basic research in this area. This study describes the viscoelastic properties of m. triceps surae and investigates the influence of static stretching. 20 males and 11 females, without a history of ankle injury, participated in this experiment. Each testee completed two sessions of seven measurements on an active omnikinetic dynamometer (PROMETT-system). The velocity of the leverarm has been kept constant during all tests (lO°/s). An interactive loop determines the stretching amplitude depending on the force exerted on this lever. The subject was fixated in an adjustable chair, the right leg extended and sustained, the left leg maximally bended in the hip to stabilize the pelvis. Further on, wooden plates were placed between the back of the chair and the pelvis to avoid any hip displacements while exerting force on the foot. After aligning the ankle axis with the axis of the dynamometer, the leverarm was manipulated to determine the moment (Mcrit) and the angle associated with a stretch just short of causing pain. The first and last measurement,of each session was an isokinetic stretch up to Mcrit (Stretch). After a short hold (200 me) in this extreme position (Hold) the same isokinetic movement, but in opposite direction, was used to relax the muscle (Relax). Between-these two 'control measurements' five identic static stretches were performed. These stretches were varied among subgroups regarding the intensity of the Stretch (90% or 100% of Mcrit) and the duration of the Hold (10s or 30 a). Netto joint moments were calculated and expressed relatively as a function of the stretching amplitude. Eighty parameters were selected in order to describe the strain-stretch curves during Stretch and Relax phases and the stress-time curves during the Hold phases. Results obtained by comparing those parameters from first and last control measurements reveal a very stable intra-individual viscoelastic behaviour of the muscle. Though, significant differences in stretching amplitude, creep and parameters describing the shape of the relax curves were observed. Differences between subgroups show a stronger influence of the intensity to the result of the static stretch compared to the influence of a longer Hold phase. In this study females had a significant smaller stretching amplitude then males. They also had less advantages of static stretching

MECHANICAL MUSCLE PROPERTIES AFTER TWO TYPES OF PLYOMETRIC TRAINING

Strength training effects may be highly specific. This suggestion is not always supported by previous research. Most training studies use strength measures to evaluate the effect of the program. It seems reasonable that a measure of strength does not fully describe the training adaptation. Therefore the design of this experiment is different. All subjects performed a set of 18 maximal contractions (isometric, isokinetic and plyometric) before and after training. Based on this set of measurements a mechanical muscle model was quantified. The coefficients of the model represent muscle properties which underlie force development (force-length, force-velocity relationship and contraction history). By studying the changes of the coefficients an attempt is made to speculate further on the underlying mechanisms which. may be responsible for the strength increase. The proposed study is designed to evaluate the use of a muscle model in investigating training programs. The subjects were divided in 3 groups: one control group (N=10) and two training groups (N=2*10). The training program involved plyometric contractions for the elbowflexors 3 dayslweek for a period of 6 weeks. These plyometric movements consisted of two successive contractions (concentric + kccentric) over an amplitude of 120" at 60"ls. The only difference between both training programs was the fact that sequence of those contractions was reversed namely concentric-eccentric for the CE-group and eccentricconcentric for the EC-group. The three groups (CE, EC. Control) showed no difference in isometric strength pre and post training. For the dynamic strength a significant improvement (P < 0.05) was observed only for both training groups. CE-training resulted in a significant change of the coefficients representing the force-velocity relationship (P < 0.05 for the ecc. part and P < 0.01 for the conc. part). The negative effect of a concentric contraction history was significantly reduced after the EC-training (P < 0.05). It can be concluded that both training groups made similar gains in dynamic force. However, analysis using the model showed that the cause of these force gains was different. For the CE-group the improvement in dynamic force can be attributed to an ameliorated force-velocity relationship whereas for the ECgroup this was due to a reduced influence of the concentric contraction historv. Specific changes in force development after training can be studied using a muscle model. These findings are a useful contribution in determining specific effects of training

STUDY OF PERFORMANCE RELATED STRENGTH TESTS FOR COMPETITION LEVEL SPRINTERS

Strength is a performance determining factor in sprinting. This study investigates the significance of a variety of isokinetic tests to control strength requirements for sprinters. Eighteen competition level sprinters &1i0 0 m-time = 10.94 s, = 0.22 s) ran a 40 meter sprint and performed 24 isokinetic strength tests on the PROMETT-system Static, concentric, eccentric and plyometric contractions were executed at velocities between 0 and 300 '1s for knee-extensors, knee flexors and ankle extensors. For each movement the torque at three different joint angles was recorded. As the performance determining factors change in relation to running distance, the correlation between the recorded torques and the running speed is graphically presented in relation to running distance (72 graphs). Per type of contraction the torque with the highest correlation with running speed was selected for further analysis. To interpret these graphs three phases are distinguished in a 40 meter sprint. Phase 1 is the phase of initial acceleration (from 0 to 10 m), phase 2 is the phase of continued acceleration (from 10 to 30 m) and phase 3 is the phase of maximum running speed (30 to 40 m). The common variance in torque and running speed data is quantified by means of the determinationcoefficient. The results indicate that isokinetic strength tests can be used to evaluate sprint related strength requirements at a competition level. 30 to 50 percent of variance in running speed within each of the three phases can be declared by a single isokinetic strength test. It may be concluded that the strength of the knee flexors determines 50 % of the variance within the phase of initial acceleration. Ankle extension torques explain 45 % of the variance in running speed within phase 2, and the strength of the knee extensors determines 33 % of variance in maximum running speed. It is also remarkable that for ankle extension only tests were selected with a high movement velocity (200°/s), while for knee extension tests were selected at lower velocities (65 and 130°/s)

Fructose-1,6-bisphosphate couples glycolytic flux to activation of Ras

Yeast and cancer cells share the unusual characteristic of favoring fermentation of sugar over respiration. We now reveal an evolutionary conserved mechanism linking fermentation to activation of Ras, a major regulator of cell proliferation in yeast and mammalian cells, and prime proto-oncogene product. A yeast mutant (tps1Δ) with overactive influx of glucose into glycolysis and hyperaccumulation of Fru1,6bisP, shows hyperactivation of Ras, which causes its glucose growth defect by triggering apoptosis. Fru1,6bisP is a potent activator of Ras in permeabilized yeast cells, likely acting through Cdc25. As in yeast, glucose triggers activation of Ras and its downstream targets MEK and ERK in mammalian cells. Biolayer interferometry measurements show that physiological concentrations of Fru1,6bisP stimulate dissociation of the pure Sos1/H-Ras complex. Thermal shift assay confirms direct binding to Sos1, the mammalian ortholog of Cdc25. Our results suggest that the Warburg effect creates a vicious cycle through Fru1,6bisP activation of Ras, by which enhanced fermentation stimulates oncogenic potency. © 2017 The Author(s)

Incubating Isolated Mouse EDL Muscles with Creatine Improves Force Production and Twitch Kinetics in Fatigue Due to Reduction in Ionic Strength

Creatine supplementation can improve performance during high intensity exercise in humans and improve muscle strength in certain myopathies. In this present study, we investigated the direct effects of acute creatine incubation on isolated mouse fast-twitch EDL muscles, and examined how these effects change with fatigue. muscle from mice aged 12–14 weeks was isolated and stimulated with field electrodes to measure force characteristics in 3 different states: (i) before fatigue; (ii) immediately after a fatigue protocol; and (iii) after recovery. These served as the control measurements for the muscle. The muscle was then incubated in a creatine solution and washed. The measurement of force characteristics in the 3 different states was then repeated. In un-fatigued muscle, creatine incubation increased the maximal tetanic force. In fatigued muscle, creatine treatment increased the force produced at all frequencies of stimulation. Incubation also increased the rate of twitch relaxation and twitch contraction in fatigued muscle. During repetitive fatiguing stimulation, creatine-treated muscles took 55.1±9.5% longer than control muscles to lose half of their original force. Measurement of weight changes showed that creatine incubation increased EDL muscle mass by 7%. sensitivity of contractile proteins as a result of ionic strength decreases following creatine incubation

Short Term Creatine Loading Without Weight Gain Improves Sprint, Agility and Leg Strength Performance in Female Futsal Players

Summary Objectives Futsal game requires players to perform frequent bouts of high-intensity activity with limited rest periods that are not sufficient for full recovery. Therefore, creatine supplementation may enhance performance by improving recovery rate. Along with this, the number of studies conducted to determine the effects of creatine on performance in the females is scarce. Thus, the main aim of this study is to identify the effects of short-term (7/day) creatine supplementation on leg strength, velocity and agility in young female futsal players. Equipment and methods A total of thirty of young female futsal players (aged: 19.83±1.13 years) participated in the study which was designed as randomized and double-blind, on a voluntary basis. Participants were randomly assigned either to creatine (n=15) or placebo (n=15) group. Over 7 days, creatine group received 0.25g/kg/day micronized pure creatine monohydrate (Creapure, Hardline Nutrition, Kavi Gıda Istanbul, Turkey) and placebo group did not take any supplements, apart from maltodextrin (Fantomalt, Nutricia, United Kingdom). Before and after 7 days of loading creatine supplementation, body weight, leg strength, velocity and agility performance of the participants were determined. The data obtained were analysed with ANCOVA statistical model. Results Creatine supplementation significantly improved 10m, 20m and 30m speed performances (P0.05). The data obtained provide that 7 days low dose creatine supplementation may be an effective approach for improving exercise capacity in female futsal players without an associated increase in body weight. Résumé Objectifs Le jeu de futsal exige que les joueurs effectuent de fréquentes périodes d’activité de haute intensité avec des périodes de repos limitées qui ne sont pas suffisantes pour une récupération complète. Par conséquent, la supplémentation en créatine peut améliorer les performances en améliorant le taux de récupération. Parallèlement à cela, le nombre d’études menées pour déterminer les effets de la créatine sur la performance chez les femmes est rare. Ainsi, le but principal de cette étude est d’identifier les effets de la supplémentation en créatine à court terme (7/jour) sur puissance des jambes, la vélocité et l’agilité chez les jeunes joueuses de futsal féminines. Équipement et méthodes Au total, une trentaine de jeunes joueuses de futsal (âgées de 19,83±1,13 ans) ont participé à l’étude, conçue comme une étude randomisée et en double insu, sur base volontaire. Les participants ont été assignés au hasard soit au groupe créatine (n=15) ou au groupe Placebo (n=15). Sur 7jours, le groupe créatine a reçu 0,25g/kg/jour de monohydrate de créatine pure micronisée (Creapure, Hardline Nutrition, Kavi Gida Istanbul, Turquie) et le groupe placebo n’a pas pris de suppléments hormis la maltodextrine (Fantomalt, Nutricia, Royaume-Uni). Avant et après 7jours de chargement de supplémentation en créatine, le poids corporel, la force des jambes, la vélocité et l’agilité des participants ont été déterminés. Les données obtenues ont été analysées avec le modèle statistique ANCOVA. Résultats La supplémentation en créatine a significativement amélioré les performances en vitesse de 10m, 20m et 30m (p<0,05), la force des jambes (p<0,05) et l’agilité (p<0,05) chez les joueuses de futsal. Cependant, en fonction de la charge en créatine, aucun changement significatif du poids corporel n’a été observé (p<0,05). Les données obtenues indiquent qu’une supplémentation en créatine à faible dose de 7jours peut être une approche efficace pour améliorer la capacité d’exercice chez les joueuses féminines de futsal sans augmentation associée du poids corporel

The creatine kinase system and pleiotropic effects of creatine

The pleiotropic effects of creatine (Cr) are based mostly on the functions of the enzyme creatine kinase (CK) and its high-energy product phosphocreatine (PCr). Multidisciplinary studies have established molecular, cellular, organ and somatic functions of the CK/PCr system, in particular for cells and tissues with high and intermittent energy fluctuations. These studies include tissue-specific expression and subcellular localization of CK isoforms, high-resolution molecular structures and structure–function relationships, transgenic CK abrogation and reverse genetic approaches. Three energy-related physiological principles emerge, namely that the CK/PCr systems functions as (a) an immediately available temporal energy buffer, (b) a spatial energy buffer or intracellular energy transport system (the CK/PCr energy shuttle or circuit) and (c) a metabolic regulator. The CK/PCr energy shuttle connects sites of ATP production (glycolysis and mitochondrial oxidative phosphorylation) with subcellular sites of ATP utilization (ATPases). Thus, diffusion limitations of ADP and ATP are overcome by PCr/Cr shuttling, as most clearly seen in polar cells such as spermatozoa, retina photoreceptor cells and sensory hair bundles of the inner ear. The CK/PCr system relies on the close exchange of substrates and products between CK isoforms and ATP-generating or -consuming processes. Mitochondrial CK in the mitochondrial outer compartment, for example, is tightly coupled to ATP export via adenine nucleotide transporter or carrier (ANT) and thus ATP-synthesis and respiratory chain activity, releasing PCr into the cytosol. This coupling also reduces formation of reactive oxygen species (ROS) and inhibits mitochondrial permeability transition, an early event in apoptosis. Cr itself may also act as a direct and/or indirect anti-oxidant, while PCr can interact with and protect cellular membranes. Collectively, these factors may well explain the beneficial effects of Cr supplementation. The stimulating effects of Cr for muscle and bone growth and maintenance, and especially in neuroprotection, are now recognized and the first clinical studies are underway. Novel socio-economically relevant applications of Cr supplementation are emerging, e.g. for senior people, intensive care units and dialysis patients, who are notoriously Cr-depleted. Also, Cr will likely be beneficial for the healthy development of premature infants, who after separation from the placenta depend on external Cr. Cr supplementation of pregnant and lactating women, as well as of babies and infants are likely to be of benefit for child development. Last but not least, Cr harbours a global ecological potential as an additive for animal feed, replacing meat- and fish meal for animal (poultry and swine) and fish aqua farming. This may help to alleviate human starvation and at the same time prevent over-fishing of oceans