The relationship of muscle strength symmetry with the symmetry of dynamic activities such as vertical jump (CMJ) and with symmetry of ranges of motion is ambiguous. Therefore, the aim of the current investigation was to assess the relationship between the flexor/extensor strength ratio and the range of motion of the knee joints and VGRF during jump in a sample of young healthy men. The sample consisted of 64 healthy, active men. The flexor and extensor torques and ranges of active and passive mobility of both knee joints were measured. Vertical ground reaction force (VGRF) was measured using two platforms. There were no significant correlations between the symmetry of muscle strength and the symmetry of ranges of motion and the symmetry of the VGRF. Therefore, using the cluster analysis, 4 subgroups were distinguished due to the size of the flexor/extensor ratio (H/Q ratio). Significant differences were found in the level of strength of the knee flexors between the clusters. Detailed analysis of muscle strength symmetry and VGRF symmetry seem to confirm the Leading Joint Hypothesis theory of motion control in multi-joint systems. It was found that the process of controlling movement by the nervous system compensates for the small asymmetries in the level of muscle strength in the knee flexors and extensors, as well as small asymmetries of VGRF.

Introduction. This paper aimed to establish relationships between the level of functional and dynamic asymmetry in advanced and intermediate-level runners and running velocity. Furthermore, evaluation of dynamic symmetry (running and vertical jump) was made using indices, taking into account the continuous character of the signals of the ground reaction force and angular positions in individual joints of the lower limb. Material and methods. Symmetry was assessed in a group of 12 Polish elite female middle-distance runners for the following parameters: 1) strength of lower limb muscles, 2) impulse of the vertical component of the ground reaction force during a CMJ jump, and 3) kinematics of a 50-m run in a straight line. Results. More advanced athletes (group A) were significantly taller and stronger than the athletes with less training experience (B). They were also characterized by a significantly longer step, a more extended swing phase, and a shorter support phase. There were no statistically significant differences between groups A and B in the level of asymmetry. Running velocity was significantly influenced by muscle strength symmetry (b = −5.77; p < 0.01) and support phase time symmetry (b = −6.64; p < 0.03). A reduction in each of these indices leads to an increase in running velocity. Conclusion. No morphological or functional asymmetry was found in female middle-distance runners with different training experience.

Background: This study assesses curved track effects on fatigue symmetry and lower limb muscle activity while taking maximum velocity running kinematics into account. Methods: Polish master class athletes were examined (age 24.6 ± 3.67 years, bm 78.9 ± 6.02 kg, and bh 186.1 ± 6.63 cm). The measurements were made on a 400 m synthetic surface athletics track. The DelSys 16 channel system was employed to measure the activity of the right and left leg muscles. The kinematic variables of the run were obtained using a 3-axis accelerometer built into the recorder. Results: The study revealed curved track effects on asymmetric muscle activity and running kinematics in the first two sections of the run. On the first curve, the symmetry index (SI) was 8.1%, while in on straight, it was 11.5%. Moreover, significantly lower values of the fatigue index b were found for the right limb (F_(3.36) = 6.504; p = 0.0152). Conclusions: A reduction of asymmetric muscle activity is linked with compensatory muscle stimulation triggered by the nervous system and with adjusting running kinematics to changing external conditions. Therefore, the main focus further research should be on the optimal interaction between stride length and frequency in relation to the muscle activity corresponding to the track geometry.

Introduction: Postural defects are a serious problem in modern society. In research on the subject, it is indicated that parents should pay special attention to their children's body posture. Basic knowledge in the field of posture defects and prevention will help prevent and deal with postural defects in children.Objectives: The aim of the study is to design and determine the reliability of a questionnaire examining parents' knowledge of postural health.Material and methods: The questionnaire development process consisted of the following steps: content and face validation, as well as reliability analysis. The questionnaire contains items assessing parents' literacy of body posture and was conducted among 55 Polish parents of school-age children and adolescents.Results: Initial results (first test-retest) for 37 participants revealed substantial reliability (0.61 to 1.00), however, it was exhibited that modifications were needed for some specific questions. After revisions and retesting (second test-retest of 18 participants), the updated questionnaire demonstrated significantly improved reliability (Cohen's kappa coefficient ranged from 0.85 to 1.00).Conclusions: The developed questionnaire is valid in terms of face and content validity, as well as reliability for assessing parents' literacy of body posture, and can potentially be used in clinical trials and practical settings.

Introduction . The aim of this study was to determine the correlations between the direction and velocity of the ball in volleyball spike. We adopted the hypothesis that the direction of an attack is dependent upon the arrangement of the pectoral girdles in the phase of flight. Material and methods. The research was carried out for four different types of attacks: from the left side of the court down the line (A) and in the cross-court direction (B) and from the right side in the same directions (C and D). Sixteen young volleyball players from a Sports Championship School run by the Polish Volleyball Federation were examined. Results . The analysis of the results showed different ball velocities in different attacks. The velocity was the lowest in attack B and the highest in attack D. Conclusions. The direction of attack was produced by hitting the ball in a non-central manner and by aligning the glenohumeral joints diagonally to the net.