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This study’s aim is to examine the effect of a combined balance and multidirectional plyometric training intervention on postural balance ability and lower limb explosive performance in U-13 male and female soccer athletes. Twenty pre-adolescent (age: 12.6 ± 1.6 years) soccer athletes followed a 6-week training intervention combining balance exercises, dynamic stabilization tasks and multidirectional plyometric exercises at a frequency of twice/week for 20–25 min, based on a progressive increase in exercise difficulty from phase A (week 1–3) to phase B (week 4–6). Pre- and post-training measurements were carried out to assess the following: (a) static balance performance in single (left, right)-legged and two-legged quiet stance trials with eyes open and eyes closed (two trials per stance and vision condition of 30 s duration) and (b) lower limb explosive performance in countermovement and squat jumps without arm swing (three trials/jump). The vertical GRF was recorded by a customized force plate (Wii, 1.000 Hz, Biovision) and offline, CoP and explosive performance parameters were calculated. The overall results showed that the static balance ability of athletes remained unaffected, while restricting their vision deteriorated their postural control. The lower limb explosive performance showed a trend for improvement; however, inter-individual variations in athletes’ responses might have obscured any effect.

The frog-inspired jumping robot is an interesting topic in the field of biomechanics and bionics. However, due to the frog’s explosive movement and large range of joint motion, it is very difficult to make their structure completely bionic. To obtain the optimal jumping motion model, the musculoskeletal structure, jumping movement mechanism, and characteristics of frogs are first systematically analyzed, and the corresponding structural and kinematic parameters are obtained. Based on biological characteristics, a model of the articular bone structure is created, which can fully describe the features of frog movement. According to the various factors affecting the frog’s jumping movement, mass and constraints are added, and the complex biological joint structure is simplified into four different jumping structure models. The jumping ground reaction force, velocity, and displacement of the center of mass, joint torque, and other motion information of these four models are obtained through ADAMS simulation to reveal the jumping movement mechanism and the influencing factors of frogs. Finally, various motion features are analyzed and compared to determine the optimal structural model of the comprehensive index, which provides a theoretical basis for the design of the frog-inspired jumping robot.

The relationship between asymmetry and performance is still undetermined in the literature. Methods of assessing asymmetry have been inconsistent and focused on the analysis of jumping asymmetry. Dual ground reaction forces are prevalent in athlete monitoring, though underutilized in asymmetry research. The purpose of this study was to assess the relationship of countermovement jump (CMJ) impulse asymmetry to performance in collegiate soccer athletes. Male and female athletes were selected from an ongoing athlete research repository database of NCAA D-I soccer athletes. All athletes contributed two maximal effort unweighted (CMJ0) and weighted countermovement jumps (CMJ20) using the mean for calculations. Propulsive phase asymmetry scores (PrPAS) and positive impulse asymmetry scores (PIAS) were calculated to determine the magnitude of asymmetry for each prospective phase. Statistically significant correlations were found between CMJ0 jump height and unweighted PIAS (r = −0.43) in females. Males had statistically significant correlations between CMJ20 jump height and weighted PIAS (r = −0.49). Neither unweighted PrPAS nor weighted PrPAS produced statistically significant correlations (r < 0.26) to their prospective jump heights. When assessing CMJ asymmetry, it is recommended to conduct both weighted and unweighted CMJ testing, utilizing PIAS as the metric to be assessed.

Knee pads have become increasingly popular among volleyball players. Given the fact high-intensity activities that are crucial to successfully playing this sport lead to an increased risk of a knee injury, the primary use of knee pads is to prevent potential injury. However, no research has been carried out to explain the effects of knee pads on the most important physical abilities in volleyball players, thus directly affecting performance. This study was undertaken to determine the effects of knee pads on the explosive power of the lower extremities, linear speed, and agility in young female volleyball players. In two separated sessions, 84 female volleyball players (age: 14.83 ± 0.72 years; height: 163.19 ± 8.38 cm; body mass: 53.64 ± 10.42 kg; VE: 5.30 ± 3.39 years) completed squat jumps (SJ), countermovement jumps (CMJ) with and without arm swing, linear sprints at 5-m and 10-m, modified t-test, and 5-10-5 shuttle test. Data analyses included descriptive statistics, paired sample T-tests and use of effect size (ES). There was no statistical difference between the two conditions for SJ (p = 0.156; ES = 0.18), CMJ (p = 0.817; ES = 0.03), CMJ with arm swing (p = 0.194; ES = 0.14), linear sprint at 5 m (p = 0.789; ES = 0.03) and 10 m (p = 0.907; ES = −0.01), modified t-test (p = 0.284; ES = 0.13), and 5-10-5 shuttle test (p = 0.144; ES = 0.19). Wearing knee pads has neither an inhibitory nor positive effects on explosive power of the lower extremities, linear speed, and agility in young female volleyball players.

The frog-inspired jumping robot is an interesting topic in the field of biomechanics and bionics. However, due to the frog's explosive movement and large range of joint motion, it is very difficult to make their structure completely bionic. To obtain the optimal jumping motion model, the musculoskeletal structure, jumping movement mechanism, and characteristics of frogs are first systematically analyzed, and the corresponding structural and kinematic parameters are obtained. Based on biological characteristics, a model of the articular bone structure is created, which can fully describe the features of frog movement. According to the various factors affecting the frog's jumping movement, mass and constraints are added, and the complex biological joint structure is simplified into four different jumping structure models. The jumping ground reaction force, velocity, and displacement of the center of mass, joint torque, and other motion information of these four models are obtained through ADAMS simulation to reveal the jumping movement mechanism and the influencing factors of frogs. Finally, various motion features are analyzed and compared to determine the optimal structural model of the comprehensive index, which provides a theoretical basis for the design of the frog-inspired jumping robot.

The aim of this study was to investigate the effects of rectus abdominis (RA) fatigue on the jumping performance and landing loads of volleyball players during countermovement jumps (CMJs) and spike jumps (SPJs). Twelve healthy university volleyball players were evaluated using a three-dimensional motion analysis system, force plates, and surface electromyography (EMG). The lowest center of mass (Min-CoM), maximum jumping height (Max-JH), angles of joints at take-off and landing, joint moment of the lower limbs, and EMG parameters of the RA, erector spinae, and lower limb muscles, when performing the CMJs and SPJs, were recorded before and after a 10 min RA muscle fatigue intervention. After RA fatigue, the Max-JH was significantly reduced, and the lowest Min-CoM was significantly increased. The take-off angles changed significantly at the ankle (SPJ), knee (CMJ), and hip (SPJ), and the plantar flexion torque changed significantly at the SPJ touchdown. The contribution ratio of the feet during SPJs and CMJs changed after fatigue. Temporary RA fatigue decreases the jump height of athletes and causes a change in the landing strategy.

Figure roller skating is a discipline composed of various movements which involve jumps, artistic figures and spins in a seamless program which has both technical and shapely difficult. A biomechanical analysis of a double salchow was performed using a 2D video analysis of one European and in two Italian roller skaters. On average, the high level (HL) roller skater showed a horizontal velocity of the center of mass higher than the average, especially in the prop stage, whereas the medium level (ML) and low level (LL) athletes reduced their velocity significantly. The spin angular velocity of the ML and LL skaters was always higher than of the HL. This phenomenon would seem to be a compensatory strategy for a lower jump height, with a reduced trunk-thigh angle and less thigh lever arm (coxo-femur/knee joints) during the take-off and landing phases of the double salchow jump.

AIM: Ballet dancers’ performance is based on the execution of complex technical skills that require an unusually large range of motion (ROM) and increased muscular power. Static stretching is commonly used to increase ROM, but it may induce a transient decrease in muscle power. However, this may depend on the population and stretching protocol. The purpose of this study was to compare the acute effect of a short (20 s) vs. a long (60 s) static stretching protocol on joint ROM and jumping performance in ballet dancers. MATERIAL & METHOD: Sixteen female professional ballet dancers (age, 25.9 ± 2.7; dancing experience, 19.6 ± 3.8 y) performed 5 days of testing using a single-leg stretching and jumping design. Baseline measurements of one-leg countermovement jump (CMJ) and a ballet technical jump with one leg (“temps levé”, TL) were performed on the first visit. On the other four visits, dancers stretched their hamstrings, quadriceps and plantar flexors for 20 or 60 s per muscle group and then performed a CMJ or a TL in a counterbalanced order. This combination of stretching and jumping resulted in four conditions: long stretch-CMJ, long stretch-TL, short stretch-CMJ and short stretch-TL. In all conditions, ankle joint ROM was measured at rest and immediately after stretching. RESULTS: ROM significantly increased following stretching (p = 0.01) with no difference between stretching protocols (p = 0.505). CMJ height decreased post-stretching following both stretching protocols (p = 0.01); however, the long-duration static stretching induced a larger decrease in jump height (p = 0.020). TL height remained unchanged after the short and the long stretching protocols (7.7 ± 2.1 to 7.4 ± 2.2 vs. 7.7 ± 2.1 to 7.2 ± 2.0 cm, respectively, p = 0.701). CONCLUSION: Both stretching protocols similarly increased ankle joint ROM and decreased one-leg CMJ height immediately post-stretching. Also, both stretching protocols did not decrease TL height, probably because dancers are able to compensate for the stretch-induced deficit in muscle power through motor coordination.

The relationship between asymmetry and performance is still undetermined in the literature. Methods of assessing asymmetry have been inconsistent and focused on the analysis of jumping asymmetry. Dual ground reaction forces are prevalent in athlete monitoring, though underutilized in asymmetry research. The purpose of this study was to assess the relationship of countermovement jump (CMJ) impulse asymmetry to performance in collegiate soccer athletes. Male and female athletes were selected from an ongoing athlete research repository database of NCAA D-I soccer athletes. All athletes contributed two maximal effort unweighted (CMJ0) and weighted countermovement jumps (CMJ20) using the mean for calculations. Propulsive phase asymmetry scores (PrPAS) and positive impulse asymmetry scores (PIAS) were calculated to determine the magnitude of asymmetry for each prospective phase. Statistically significant correlations were found between CMJ0 jump height and unweighted PIAS (r = −0.43) in females. Males had statistically significant correlations between CMJ20 jump height and weighted PIAS (r = −0.49). Neither unweighted PrPAS nor weighted PrPAS produced statistically significant correlations (r < 0.26) to their prospective jump heights. When assessing CMJ asymmetry, it is recommended to conduct both weighted and unweighted CMJ testing, utilizing PIAS as the metric to be assessed.

Knee pads have become increasingly popular among volleyball players. Given the fact high-intensity activities that are crucial to successfully playing this sport lead to an increased risk of a knee injury, the primary use of knee pads is to prevent potential injury. However, no research has been carried out to explain the effects of knee pads on the most important physical abilities in volleyball players, thus directly affecting performance. This study was undertaken to determine the effects of knee pads on the explosive power of the lower extremities, linear speed, and agility in young female volleyball players. In two separated sessions, 84 female volleyball players (age: 14.83 ± 0.72 years; height: 163.19 ± 8.38 cm; body mass: 53.64 ± 10.42 kg; VE: 5.30 ± 3.39 years) completed squat jumps (SJ), countermovement jumps (CMJ) with and without arm swing, linear sprints at 5-m and 10-m, modified t -test, and 5-10-5 shuttle test. Data analyses included descriptive statistics, paired sample T -tests and use of effect size (ES). There was no statistical difference between the two conditions for SJ ( p = 0.156; ES = 0.18), CMJ ( p = 0.817; ES = 0.03), CMJ with arm swing ( p = 0.194; ES = 0.14), linear sprint at 5 m ( p = 0.789; ES = 0.03) and 10 m ( p = 0.907; ES = -0.01), modified t -test ( p = 0.284; ES = 0.13), and 5-10-5 shuttle test ( p = 0.144; ES = 0.19). Wearing knee pads has neither an inhibitory nor positive effects on explosive power of the lower extremities, linear speed, and agility in young female volleyball players.