This study investigated the effects of knee joint angle on muscle activation, exerted torque, and whether the knee angle affects the muscle activation–torque ratio. Nine healthy adult male participants participated in the study. They performed maximal voluntary isometric contraction (MVIC) at six (80°, 90°, 100°, 110°, 120°, and 130°) different knee joint angles (i.e., angles between the thigh and shin bones). Their maximal torque was assessed utilizing an isokinetic chair, while their muscle activation (root mean square [RMS]) was assessed using an eight-channel single differential surface EMG sensor. For the purposes of the torque–knee angle relationship and muscle activation–knee angle relationship, the torque and RMS were normalized relative to the maximal value obtained by each participant. To evaluate the muscle activation–torque ratio in function of knee angle, RMS was normalized relative to the corresponding torque obtained at each knee angle. Repeated measure analysis of variance was used to investigate the effects of knee angle on muscle activation, torque, and muscle activation–torque ratio. There was a significant effect of knee joint angle on normalized torque (F = 27.521, p < 0.001), while the activation of vastus lateralis and vastus medialis remained unchanged. The changes in knee angle affected the muscle activation–torque ratio of vastus lateralis (Chi-square = 16.246, p = 0.006) but not the vastus medialis. These results suggest that knee joint angles from 80° to 130° provide a stable milieu for muscle electrification, while mechanical factor such as knee joint angle (i.e., lever arm length) affect the torque output when one needs to contract quadriceps maximally during the isometric contraction.

Background: This study investigated whether diaphragmatic breathing intervention could lead to acute improvements in trunk and shoulder mobility and pulmonary function in healthy young adults. Methods: Twenty-six physically active males (aged 24.3 ± 2.0 years, body height of 182.9 ± 6.4 cm, and body weight of 82.8 ± 10.4 kg) were randomly assigned to either an experimental or a control group. The experimental group underwent a 22 min diaphragmatic breathing intervention in a lying position. The control group lay passively, breathing naturally. Mobility assessments (chest expansion, thoracic spine rotation, lateral trunk flexion, and shoulder girdle mobility) and pulmonary function tests (forced vital capacity, forced expiratory volume in one second and their ratio) were conducted before and after the intervention. Results: Only experimental group showed significant improvements after the intervention (p ≤ 0.01) in the chest expansion (+22.2%, ES = 0.62), thoracic spine rotation (+21.7%, ES = 0.76 on the left and +23.3%, ES = 0.84 on the right side), lateral trunk flexion (+11.7%, ES = 0.62 on the left and +15.4%, ES = 1 on the right side), shoulder girdle mobility (+20.2%, ES = 0.44 on the left and +21.5%, ES = 0.38 on the right side), forced vital capacity (+4.7%, ES = 0.39) and reduction (p ≤ 0.01) in ratio between forced expiratory volume in one second and forced vital capacity (−4.6%, ES = 0.47). Conclusion: The results revealed that a 22 min diaphragmatic breathing intervention could immediately improve trunk and shoulder mobility and pulmonary function, likely due to anatomical relationships and more efficient use of respiratory muscles, especially the diaphragm.

Previous studies indicate that there is a large influence of the starting reaction time (RT) on sprint performance, but also that some recent changes in athletic rules may affect this correlation. This study aimed to examine the relationship between RT and results in: men’s (M60mH) and women’s (W60mH) disciplines 60 m over hurdles, 60 m hurdles in the heptathlon (H), 60 m hurdles in the pentathlon (P) at the recently held World Indoor Championship 2022 (WIC). The aim was also to determine whether there are differences in RT between M60mH and W60mH, M60mH and H, W60mH, and P, and between H and P. The study included 170 competitors who competed at the WIC. Pearson’s linear correlation coefficient (r) was used for correlation analysis, and the t-test for independent samples was used to examine differences between groups. A statistically significant correlation (r=0.23, N=72, p=0.05) was found between the results and RT in W60mH when observing the entire sample of participants (r2 = 5.29). Considering that in H (r=0.42, N=10, p=0.23, r2=0.18) and P (r=0.54, N=12, p=0.07, r2=0.29), a much higher correlation was obtained between results and RT than in competitors in the 60 m hurdles event, we believe that this is a consequence of different athletic rules that refer to a false start. There are no significant differences between RT for M60mH and W60mH, M60mH and H, W60mH, and P, and between H and P. Coaches should pay attention to developing all parts of the sprint race, including the reaction time.

Countermovement jump (CMJ) is an element of many sports techniques and has an important role in the overall performance, both when performed at maximal and submaximal intensity. This paper aims to investigate changes in biomechanical and neuromuscular variables that are responsible for controlling different submaximal intensities of the CMJ. 8 healthy and uninjured volleyball players from the first league of the Republic of Serbia, average age 21.9 ± 1.9 years, average body height 191.6 ± 9.2 cm, average body weight 83.1 ± 7.1 kg were included in the study. Subjects performed CMJ at three different jump heights (approximately 65%, 80%, and 95% of the maximal height). For the analysis of electromyographic data, the value of root mean square analysis was used separately for the amortization phase and the jump phase, for the following muscles: m. gluteus maximus (GlutM), m. rectus femoris (RF), m. biceps femoris (BF), m. vastus lateralis (VL), m. tibialis anterior (TA) and m. gastrocnemius medialis(GastM).Kinematic and kinetic variableswere monitored: vertical center of mass displacement in the amortization phase [m], the center of mass height at take-off point [m], jump height [m], jump speed [m/s], angular displacement in the ankle, knee and hip joint [rad], maximal vertical ground reaction force [N/ kg], vertical stiffness [kN/m/kg], the torque of the ankle, knee and hip joint [Nm/kg]. The change in jump height (65, 80 and 95%) did not have a significant effect on the change in activation for most muscles (p≥0.05), except for GastM where a tendency towards increase was observed (p=0.066). During jump phase, the activation of VL, BF, GlutM, TA muscles significantly increased compared to the amortization phase (p≤0.05). The torque in the hip joint increased significantly with increasing jump height (65<80=95%) (p=0.028). During amortization phase, the values of vertical center of mass displacement increased significantl y between each jump height (65<80<95%) (p≤0.05), while the values of vertical stiffness decreased with increasing jump height, where significant differences were observed between 80% and 95% of maximal jump height (65=80<95%) (p=0.012). Angular displacements in the knee and hip joint increased significantly with increasing jump height (65<80<95%) (p≤0.05) while no changes in angular displacement in the ankle joint were observed (p≥0.05). The results of the research show that the increase in the jump height is related to an increase in the amortization phase, due to an increase in angular displacements in the knee and hip joint, as well as an increase in torque of the hip joint.

Lumbar disc herniation, a growing condition, significantly impacts work productivity, mental health, and quality of life. It alters functional movement patterns and causes improper compensatory body positioning, leading to muscle dysfunction. Physical exercise is a key treatment for chronic cases. This case study examined a 37-year-old male with moderate triple lumbar disc herniation and degenerative disc changes at L3-L4, L4-L5, and L5-S1. The subject followed a 10-week home-based exercise program performed 4 to 5 times weekly for 45 minutes per session. The program consisted of variations of body-weight exercises, supplemented with additional equipment, and progressively increased in intensity and volume, targeting hip joint mobility and strengthening of deep back, abdominal, and thigh muscles. Initial and final assessments included the Pain Detect test, the Short Form Health Survey-36 on quality of life, Manual Muscle Testing (MMT), Functional Movement Screen (FMS), and body composition analysis. Questionnaires indicated significant pain reduction and improvements in physical condition and psychosocial well-being. MMT improved from 4 to 5, FMS from 2 to 3, and body composition showed positive changes: weight (+1.5%), body water (+3.4%), skeletal muscle (+2.8%), and body fat (-6.6%). The subject reported substantial pain reduction, improved physical condition and psychosocial well-being, as well as enhanced muscle strength, functional movement patterns, and body composition. This case study highlights the program’s effectiveness in treating lumbar disc herniation and enhancing quality of life. Additionally, the program is suitable for preventing lumbar disc herniation and improving overall quality of life in the broader population. How to cite: Randow de Almeida, K., Kapeleti, M., Stevanović, V., Mrdaković, V., & Macura, M. Enhancing quality of life through physical exercise in a patient with triple lumbar disc herniation: A longitudinal case study. Exercise and Quality of Life. Advance online publication. https://doi.org/10.31382/preprint.000009

The purpose of this study was to analyze kinematic variables of side volley in elite soccer players, as well as examining kinematic variables adjustment in relation to the change of velocity and height of incoming ball. Thirty professional soccer players participated in this study. The experimental protocol implied kicking the ball towards the subject at three different velocities and three different heights. The analysis included a total of the following seven dependent variables: Maximum linear velocity of the foot, the knee and the hip (V_FOOT_max, V_KNEE_max, V_HIP_max), Maximum knee and hip joint angular velocities (W_KNEE_max, W_HIP_max), Distance between the foot and the hip at impact with the ball (D_hip.foot_tk), and Angle between the shoulder and hip axis and the hip and foot axis at impact with the ball (α_SHF_tk). Also, for the purpose of descriptive kinematic analysis, the variables of changed angles and hip and knee joint angular velocities were used in different phases of side volley performance, as well as the variables of changed linear velocity of the foot, the knee and the hip. The variables of side volley kinematics were measured with the 3D kinematic analysis system (Qualisys). The effects of the ball height and velocity, and their interaction, on dependent kinematic variables were tested by using the statistical method of two-way analysis of variance with repeated measures (two-way ANOVA). The velocity and height of the incoming ball had a significant effect on V_ FOOT_max in the sense that, as ball velocity grew, V_FOOT_max increased as well, while as ball height increased, V_FOOT_max dropped. A similar effects of the ball velocity and ball height was observed for V_ HIP_max, but is observed only a tendency towards statistical significance. Also, it was observed that increased speed of the incoming ball affected increase of D_hip.foot_tk, as well as α_SHF_tk, while values of W_HIP_max were decreased. The statistical analysis revealed that changes in the mechanical conditions in which side volleys were performed such as a different velocity/height of the incoming ball affected the modulation of the velocity of the farthermost proximal and distal ends of the kinetic chain/hip and foot joints, while the knee joint function was primarily to fine-tune the distance between the subjects' position and the ball.