Football is an intermittent sport with a great number of short and explosive actions. These characteristics of the game require a good level of anaerobic power. The main field tests used as indicators of the development of the anaerobic energy system were the jumps in the vertical plane. The same tests also measured the strength of the lower limbs. We presume that the explosive power of the lower limbs characterizes the development of the alactic anaerobic energy system and strength capacity at the same time. In that case the explosive power of the lower limbs was an important component of the conditioning and strength training of football players. There was a great variety of methods and devices which registered vertical jump height. From this point of view, we wanted to add our study to the research work in the specialized literature. The purpose of this study was to analyze the differences of the jump height measured via two devices. We used the following methods of research: accelerometry, chronometry and statistical analysis. We studied the vertical jump height of 32 football players of the Youth Academy of PFC “Levski”– Sofia at the age of 13,4. In the research the participants performed three jump tests (squat jump [SJ], counter movement jump [CMJ] and counter movement jump with arm swing [CMJA]) as the jump height was measured via accelerometer and Infrared platform. The results from these two devices were compared via Bland Altman plot and calculation of Intraclass correlation coefficients [ICC]. The results of ICC between the two devices showed very strong correlation of the results for the three tests (SJ (R= .91), CMJ (R= .92) and CMJA (R= .87)). The results of the ANOVA showed statistical difference between the measured jump heights (p< .05 for all test, systematic bias was equal to: SJ=15.6; CMJ=15.2; CMJA= 19.5 and effect size (η2 ) was large SJ= .65; CMJ= .69; CMJA= .65) for the three different types of jump. Conclusions:1) Both of the devices showed good consistency of the collected results; 2) The data collected from the two devices showed significant difference of the jump heights.

The half-marathon originated from the marathon as its length is half a marathon or 21.0975 km. This discipline is one of the newest in the World Athletics program, as the first major championship of this distance was in 1992 in England. Even earlier, the running community created distance as an alternative to marathon running in the 50s of the 20th century. Despite its relatively long history, there is little data on the biomechanical indicators of the competitors participating in the discipline. Hence, the present study aims to determine the leading indicators characterizing running speed in the half-marathon discipline and the influence of fatigue on these indicators. To achieve the study's goal, we implemented the following tasks: 1) Measurement of the main characteristics of the running speed in 3 sections of the racing distance, 2) Determination of the variability of these indicators. To solve the study tasks, we used video analysis and statistical methods. After the analyses, we find differences in the length and frequency of the strides of competitors with different qualifications. Highly trained athletes (HT) had a more even pace (1:00-3:04 min per section) than moderately trained athletes (MT) (3:25-5:19 min per section). HT athletes had greater stride length (1.61-1.70 m) than MT athletes (1.50-1.54 m) in all sections. MT athletes rely more on stride frequency than on stride length to increase their movement speed. HT athletes are opposite MT athletes. Conclusions: 1) The results obtained show the possibilities for using drones for the needs of kinematic analysis in running 2) From the differences in running speed, we can determine that VT athletes manage to distribute their efforts more evenly over the competition distance than the MT athlete; 3) The decrease in speed at the end of the competition distance in VT athletes is mainly due to the shorter stride length.

Background/Objectives: Maintaining an upright posture is a complex, adaptive neurophysiological process that relies on a set of stereotypical muscle synergies. Despite extensive research on postural control, the interaction between muscle dynamics and ground reaction forces during progressive loading remains poorly understood. Methods: Twenty-five healthy men, aged 21–25, performed a 30 s quiet standing task on a tensometric platform. The protocol involved seven loading levels—from no load to higher loads using progressive weights in a backpack. The three components, Rx, Ry, and Rz, of the ground reaction force (GRF) and surface electromyographic activity from six muscles of the lower limb were recorded, namely medial (GAM) and lateral heads (GAL) of m. gastrocnemius, rectus femoris (RF), and vastus lateralis (VL) from m. quadriceps femoris, m. biceps femoris (BF), and m. semitendinosus (ST). The recently developed intercriteria analysis (ICrA) was utilized to enhance understanding of the central nervous system’s adaptive mechanisms under changing load conditions. Results: The ICrA results show that the RF–VL muscle pair is stable and does not depend on load, while the BF–ST pair is semi-stable across different weights. Also, ICrA indicates a significant increase in synchronization between specific muscle groups at higher load levels, suggesting the recruitment of additional muscle coupling. Regarding the influence of increasing weight (W) on GRF, the analysis reveals a positive consonance relation between W and Rz in 100% of subjects. Conclusions: The study shows that during progressive external loading, the central nervous system maintains vertical stability by reorganizing muscle coupling. Some of these are specific to individuals. Coactivation of the antagonistic muscle pairs at higher loads suggests a transition from a basic to a more complex adaptive strategy.

Volleyball is an intermittent sport dominated by the ability of competitors to perform explosive movements of both the lower and upper limbs. We find many studies related to the sport in the methodological literature, but most of them consider only one aspect. From this perspective, the present study aims to determine the differences in the manifestation of anaerobic power potential in volleyball players. To achieve the study's goal, we solved the following tasks: 1) Determining the level of development of indicators characterizing anaerobic potential in male and female volleyball players. 2) Determining their correlations 3) Comparing their level of development. We used speedometry, chronometry, force plate tests, anthropometry, and statistical methods (descriptive statistics, correlation, and comparative analysis) to solve the research tasks. After the analysis, we obtained the following results. The average values ​​for the individual tests for men and women show significant homogeneity. In all indicators, men have better indicators than women. The interrelationships among the studied indicators show that in women, there is a clear transfer of test results characterizing the anaerobic potential of the lower extremities, without this power being transferred to the upper extremities. Meanwhile, men tend to a complete transfer of anaerobic potential. Conclusions: Men and women demonstrate a good level of development of the explosive power abilities of the lower extremities and less of the speed abilities. These results indicate an incomplete deployment of upper-extremity explosive-power capabilities in women.

There are a large number of publications related to conditioning in volleyball and in general. However, a very small part of them are related to the development of motor abilities in an age aspect. Such a study would be very difficult to implement, but at the same time, it would be beneficial in terms of the selection and sports orientation of youth volleyball. Volleyball as a sport has developed extremely dynamically in recent years, which makes it even more demanding in terms of fitness. The basic skills necessary for successful implementation in sports are complex and based on the athletes‘ ability to jump, sprint, and hit. From this point of view, the interest in this research was dictated, with the primary goal of determining the values of the main signs related to the volleyball game and compiling normative tables for control and assessment of preparedness. The research tasks also arise from the goal set in this way. To investigate the differences in the main essential characteristics of the volleyball game regarding age. To propose standards of control and evaluation. The methods we used to solve the problems are anthropometry, chronometry, tensiometry, speedometry, and mathematical-statistical methods (frequency, variation analysis, and sigma method). Results: The most significant increase in women was observed in the results of the jump tests and the speed of the serve (over 20 %) and smaller within 10% in the running tests. We attribute these results to the fact that the listed movements emphasize the training and competition process. Based on the obtained results, norms for evaluating the readiness of the contestants have been drawn up.

Adolescents’ physical activity is and must be an essential part of their daily routine for proper and balanced growth and development. The use of accelerometry, a method that records the motor activity time spent in a lying or sitting position over twenty-four hours, is well-known. The actual data about a person’s movements enables us to be accurate and even to analyze the quantity and quality of those movements. We examined 135 children (mean age 129 months) with accelerometers Axivity model AX3, positioned around the wrist around the non-dominant arm. Based on consults, we established average values per twenty-four hours, namely – an average of 38.32% of the time children spent in a sitting position, 6.41% (92 min) they were engaged in a low activity, 15.42% (222 min - in a moderate activity, 1.79% (26 min) - in a high activity; and 38.06% of the time they spent sleeping. We found a weak correlation dependence r = -.263 (95%) between the body fat and the duration of the time spent in high activity.