Amy S. Albers, Jerry R. Thomas, Katherine T. Thomas: Development of rapid aiming movements: index of difficulty and movement substructure Purpose. The purpose of this experiment was to evaluate the developmental differences in movement microstructure as a function of target width and movement length manipulations in children and adults. Basic procedures. Children, 6 years old (n = 20) and 9 years old (n = 20), and adults (n = 20) performed four rapid aiming tasks using the arm and hand. Index of difficulty (from the easy to difficult as estimated by Fitts` law) was used to create four tasks levels with all participants performing 15 trials at each level. Task performance was measured by speed of movement which was subdivided into the ballistic and feedback control phases using velocity and acceleration profiles. Main findings. Results showed that participants decreased the portion of primary submovement for smaller targets and longer movements and these changes were proportional for children and adults. Conclusions. Based on their small ballistic phase of the movement, children appear to have a limited amount of the movement programmed and use feedback control for most of the movement distance and time. Adults have a substantially greater proportion of the movement time and distance in the ballistic phase leading to faster movements with fewer corrections. François Huot-Marchand, Xavier Nesi, Michel Sidney, Morgan Alberty, Patrick Pelayo: Is improvement in performance linked to higher stroke length values in top-level 100-m front crawl swimmers? Purpose. This study aimed to conclude on the determinant parameter of high-level improvement at the latest stage of sport development. Following literature conclusions, the hypothesis tested was that stroke length is the main factor to enhance to be successful in swimming. Basic procedures. From standard race analysis protocol, the stroking parameter variations (speed, S; stroke length, SL; stroke rate, SR; and stroke index, SI) were analysed in 14 high-level swimmers who have improved their performance in the 100-m freestyle final at French or European championships, each final being separated by two years. Main findings. The results showed a significant improvement of S averaging 1.89 ± 0.05 vs 1.95 ± 0.07 m · s-1 and corresponding to a mean time difference of 1.06 s. No significant differences were noticed in average values of SI (4.07 ± 0.26 vs 4.22 ± 0.27 m2 · s-1· cycles-1; p = 0.08), SL (2.15 ± 0.14 vs 2.17 ± 0.11 m · cycle-1; p = 0.59) and SR (52.98 ± 3.74 vs 53.95 ± 3.11 cycles · min-1; p = 0.11). Turn time was significantly shorter in the second race (p < 0.01) but no significance difference was reported in start and finish times (p > 0.05). All stroking parameters were stabilized during the race between the first and the second 50-m except SR in the second and best race and SI in both races. In the fastest race, first lap SR and last lap SI were higher than in the slowest race (p = 0.03 and p = 0.02, respectively). A correlation was reported between the SL and SR evolution from the first to the second race (r 2 = 0.86 at p < 0.05) and showed the interdependence of SR and SL. Five combinations between SR and SL have been observed in the sample studied. 1: increase in both SL and SR for 3 swimmers; 2: increase in SL and decrease in SR for 4 swimmers; 3: increase in SL and stabilization of SR for 1 swimmer; 4: increase in SR and decrease in SL for 5 swimmers; and 5: increase in SR and stabilization of SL for 1 swimmer. Conclusions. Results led to the conclusion that improvement at high level is not only linked to variations in SL. Alternatively, the choice of high SR values in the first lap could be a strategy chosen by swimmers to limit local muscular fatigue caused by high SL values, and permit to achieve better stroke technique at the end of the race. Unfortunately, no information about training programs was available, and one could not conclude that this strategy is linked to training contents. Finally, the present results highlighted that strategies emphasizing other parameters such as SR or turns should not be considered as ineffective, especially at top level. Sona Vodicková, Aleš Lufinka, Tomáš Zùbek: Application of the dynamographic method in Alpine skiing Purpose. The basic goal of our work was to measure the reaction forces between the ski and the plate during carving turn. Basic procedures. We constructed a special measuring device, which is able to measure the force field between the ski and the slope. 15 skiers with different skiing skills participated in the experiment. We examined short opened and closed carving turns. Main findings. In the group of skiing professionals, we could observe load of the inner and outer ski in the steering phase of the open carving turn 50% on the inner edge of the outer ski and 50% on the outer edge of the inner ski during the turn. In the closed carving turn we found the load of 71 to 92% on the inner edge of the outer ski in the group of skiing professionals. The same ratio of the loads in the closed turns was observed in the group of lectors. Conclusions. Our study helped to reveal some differences between the technique of racing skiers and that of public skiers. Carving skis enables making a turn with loading the outer as well as the inner ski. During a carving turn (in a group of racing skiers and ski instructors) there is a greater load on the inner ski in the initial phase, which was not possible with "normal" skis earlier. In practice, this means that it is necessary to focus on loading of the outer edge of the inner ski, which is necessary for an ideal spatiotemporal solution of the carving turn. Marek Rejman, Bartosz Ochmann: Application of artificial neural networks in monofin swimming technique assessment Purpose. The aim of our study was to analyze leg and monofin movements in the context of the monofin swimming technique modelling. The neural net model, empirically verified, creates an objective tool to control and assess the effectiveness of the technique level. It is also a starting point for predicting performance. Basic procedures. Eleven swimmers from the Polish Junior Monofin Swimming Team participated in the study. They swam 25 m underwater at maximum speed. Strain gauges were attached in the waist and in the middle of the monofin they used. The forces flexing the fin at the indicated points in reaction to water resistance were recorded in synchrony with the paths and time coefficient of the leg and fin movements. The kinematic parameters were collected using an underwater digital camera and converted by the SIMI® System. Main findings. The raw data were used to develop a neural network - the basis for the creation of a model of the monofin swimming technique. The level of adequacy of the features observed points to the hierarchic structure of the parameters determining the swimmer`s maximum speed. A non-linear character of the interdependences provides information on the values of the parameters in relation to swimming speed. The results reveal optimal parameter values for the swimmer whose speed is the highest. Conclusions. The analysis of the parameters` deviation from the calculated optimum enables us to draw conclusions on the causes of the speed change during the swimming cycle. The model presented here contributes to determination factors which allow high swimming speed to be generated. Malgorzata Slowiñska-Lisowska, Marek Mêdras: Psychogenic alimentary disorders in athletes Psychogenic alimentary disorders are numbered among conditions whose incidence has significantly increased in the last decade. The best known and diagnosed ones include anorexia nervosa and bulimia. People with anorexia starve themselves, avoid high-calorie foods and exercise persistently in order to purposely decrease their body weight. Bulimia is an obsession with food and weight characterized by repeated binging followed by compensatory behavior such as induced vomiting or excessive exercise. Both disorders are followed by numerous somatic changes and their treatment is very difficult and not always successful. Alimentary disorders become more and more common in athletes. Caloric, quantitative and qualitative deficiency in basic nutrients, characteristic of these disorders, may lead to endocrinal dysfunctions, premenopausal osteopenia or osteoporosis and also increase the risk of muscle or bone injuries. Physical education teachers, sports instructors or trainers should pay more attention to early symptoms of alimentary disorders in young people and persuade them to contact a specialist for appropriate diagnosis and treatment. Gracyna Lutoslawska, Marzena Malara, Marlena Zolnowska: Glucpse-free fatty acid cycle and its role in muscle metabolism The reciprocal relationship between lipid and carbohydrate oxidation was described over forty years ago by Randle in isolated rat heart and diaphragm and named glucose-free fatty acid cycle. Nowadays, the cycle operation has been well-established in lipogenic tissues (e.g. liver) with the key role of malonyl-CoA, a product of acetyl-CoA carboxylase reaction (ACC), and a potent allosteric inhibitor of carnitine palmitoyl-transferase I (CPT I) responsible for free fatty acids (FFA) transport into mitochondria and FFA oxidation. It is postulated that in resting striated muscle substrates' availability and malonyl-CoA synthesis play an important role in the regulation of FFA oxidative metabolism. On the other hand, there is a wealth of studies indicating that the active FFA (acyl-CoA) inhibit oxidative glucose disposal. However, the operation of glucose-free fatty acid cycle in working muscle is still a matter of debate, but recent data have indicated a crucial role of malonyl-CoA in the regulation of CPT I activity, FFA transport and oxidation. In addition, numerous studies have revealed a substantial role of 5'-AMP-activated protein kinase (AMPK) in the regulation of malonyl-CoA synthesis, since it phosphorylates and deactivates ACC - catalyzing acyl-CoA conversion into malonyl-CoA. Significant elevation in AMPK activity in contracting muscle depresses ACC activity and inhibits malonyl-CoA synthesis. Additionally, it has been postulated that AMPK activates malonyl-CoA decarboxylase responsible for malonyl-CoA degradation. In consequence, in the working muscle, the malonyl-CoA level decreases - due to inhibited synthesis and concomitant increased degradation. Since the elevation in AMPK activity has been noted both during intensive, short-term and low-intensity prolonged muscular work it seems feasible that FFA oxidation provides energy to the muscle at earlier stages of contraction than it is commonly accepted. Artur Jaskólski, Katarzyna Kisiel-Sajewicz, Renata Andrzejewska, Wioletta Brzenczek, Zdzislaw Adach, Anna Jaskólska: Speed of skeletal muscle relaxation depends on female hormones fluctuation Purpose. The aim of the study was to determine the influence of the female hormones fluctuation during the menstrual cycle on the relaxation speed changes of knee flexors and extensors. Basic procedures. Fifteen physical education students with a regular menstrual cycle, not using contraceptive pills, were tested during the ovulatory and luteal phases of the menstrual cycle. Relaxation from maximal voluntary contraction was measured during knee extension and flexion using the Biodyna dynamometer. The estradiol and progesterone levels were marked using the chemoluminiscence method. The following rates were calculated: slow relaxation (SRR), fast relaxation from 20%-5% of end force (FR20%-5%), and maximal relaxation rate (MRR). Main findings. The estradiol and progesterone levels were higher in the luteal phase than in the ovulatory phase. During knee flexion there was a positive correlation between the percentage changes in the FR20%-5% and in estradiol level (R = 0.715), and a negative one between the percentage changes in FR(20%-5%) and in progesterone level (R = -0.910). Moreover, there was a negative correlation between the percentage changes in MRR and in progesterone level (R = -0.705). For knee extensors the respective correlation coefficients were opposite to that in knee flexors, however none of the correlations were statistically significant. Conclusions. 1. The influence of estradiol fluctuation within the ovulatory and luteal phases of menstrual cycle on changes of relaxation from MVC is opposite to that of progesterone, which most likely results from progesterone functioning as an inhibitor of estrogens. 2. The influence of estradiol and progesterone fluctuation during the ovulatory and luteal phases of menstrual cycle on relaxation from MVC occurs mainly via central nervous system mechanisms (not at muscle cell level) since this effect was seen in knee flexors but not extensors and in fast but not in slow relaxation. 3. Compared to the slow relaxation, the mechanisms responsible for the fast relaxation are more sensitive to sex hormones fluctuation during the ovulatory and luteal phases.
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