The countermovement jump is a popular measurement modality to evaluate muscle power in sports and exercise. Muscle power is essential to achieve a high jump, yet the well-coordinated movement of the body segments, which optimizes the stretch-shortening cycle (SSC) effects, is also required. Among the proposed explanations of SSC effects, this study investigated whether the ankle joint kinematics, kinetics, and muscle-tendon interaction depend on the level of jump skill and the jump task. Sixteen healthy males were grouped as a function of their jump height (High jumpers; greater than 50 cm, Low jumpers; less than 50 cm). They were instructed to jump with two intensities; light effort (20 % of their height) and maximal effort. Joint kinematics and kinetics of the lower limbs were analyzed using a 3-dimensional motion analysis system. The muscle-tendon interaction was investigated using B-mode real-time ultrasonography. As the jump intensity increased, all participants jumped with increased joint velocity and power. However, the high jumper shows less fascicle shortening velocity (-0.2 ± 0.1 m/s) than the low jumper group (-0.3 ± 0.1 m/s) and greater tendon velocity, which indicated the capability of elastic energy recoil. In addition, the delayed onset time of ankle extension in the high jumper implies better use of the catapult mechanism. The findings of this study showed that the muscle-tendon interaction differs depending on the jump skill level, suggesting a more efficient neuromuscular control in skilled jumpers.

Introduction: Ballet-based dance training emphasizes the equal development of both legs. However, dancers often perceive differences between their legs during balance or landing. There still needs to be more consensus on the functional difference between dominant (D) and non-dominant legs (ND). Therefore, this study investigated both legs’ neuromuscular strategy in single-leg balance and landing based on leg dominance. Methods: Thirteen female dancers (age: 22.2 ± 2.8 years) with no history of ankle injuries in the past year participated in the study. Based on the questionnaire, the dominant leg was set, which legs were preferred to balance, generate strength, and land. Joint kinematics and ground reaction force (GRF) were analyzed using a three-dimensional motion analysis system and force plates during single-leg balance (SLB), passé balance (PB), sissone simple (SS), and sissone ouverte (SO). The tibialis anterior (TA), medial gastrocnemius (MG), peroneus longus (PL), and gluteus medius (GM) activation were measured by wireless surface electromyography (EMG). Displacement (cm) of the center of pressure and the dynamic postural stability index (DPSI), a balanced score post dynamic tasks, were calculated. Results: Bilateral leg balance ability was observed based on joint kinematics and DPSI during SLB, PB, SS, and SO. Higher TA activity was noted during PB in ND legs than in D legs ( P = .038). PL activation was significantly increased in ND legs (69.3 ± 34.4%) than in D legs (45.6 ± 19.2%) before contact during SS and SO ( P < .05). After landing with ND legs, dancers regulated postural stability with increasing TA activation ( P < .05). Conclusions: Pre-activation of PL before landing with ND legs increases ankle stiffness, enhancing stability. Conversely, D legs achieve balance with lower activation levels. The findings highlight significant differences between legs in dancers, suggesting that leg dominance should be considered in future training and performance strategies.

Reaction time is important to determine the performance of fencing. The purpose of this study was to investigate the reaction time and muscle activity and compare the movement among genders during Marche-fente. Fifteen Korean national Fleuret fencing athletes participated and were instructed to perform Marche-fente. Reaction time was measured with Plug & Play equipment and muscle activation was obtained by electromyography. The male athletes (0.94 ± 0.08 s) were faster than female athletes, who a performance of 1.03 ± 0.05 s. As the knee extensors activation was increased, the movement and response time was shorter (rectus femoris (RF); r = −0.526, p < 0.05, vastus lateralis oblique (VLO); r = −0.628, p < 0.05). In phase 1, men activated more knee extensors in the dominant leg, whereas the activation of knee flexors was increased to maintain a stable posture in women. Additionally, women used other muscles instead of large muscles such as RF and VLO in phase 2. In conclusion, female athletes activated knee flexors rather than knee extensors when moving the center of mass or generating a greater force. Less use of knee extensors is associated with knee injuries; therefore, exercise which activates knee extensors is required for females.

After COVID-19, face-to-face learning was changed to online learning. However, very few effective online learning methods were available regarding physical education. Therefore, this study aimed to examine the modeling effects on learning ballet movement in the online system. We aimed to find effective modeling presentations based on objective information, expert assessments, and a kinematic approach. The study included 36 individuals who were divided into an expert modeling group, a self-modeling group, and controls. Participants performed 60 trials of Pas de basque in the acquisition phase and 10 trials without a demonstration video after 24 h. 10 min later, the reversed Pas de basque was conducted for the retention test. All groups showed improved performance after the acquisition phase, which indicated that the modeling presentation was effective despite adopting an online learning system. However, higher expert scores and more accurate joint movements were shown in the expert modeling group compared to the other groups. Therefore, expert modeling seems to be the most effective method for learning high-difficulty tasks with jumps and turns.