[Introduction] Electrical stimulation is widely used in the field of rehabilitation for purposes such as promoting muscle contraction, enhancing muscle strength, and alleviating pain. In particular, electroacupuncture (EA), a therapy that delivers low-frequency electrical stimulation through acupuncture needles, is commonly used in the acupuncture field and is considered effective for providing direct stimulation to deep tissues. However, detailed evaluations of muscle contraction dynamics induced by EA remain insufficient. The purpose of this study was to quantitatively assess the lateral displacement of muscle and adipose tissues during EA using ultrasound imaging and motion tracking techniques, and to clarify the differences in dynamic behavior among anatomical regions.[Subjects and Methods] Seven healthy young males participated in this study. EA was applied to the medial head of the right gastrocnemius muscle. Longitudinal ultrasound images were obtained, and three 20-second video recordings were collected. Using motion tracking software, lateral displacement was calculated for four regions: fat, gastrocnemius (shallow and deep layers), and soleus. Additionally, gliding distances were defined between fat and the shallow layer (DF), and between the deep layer and soleus (DIF), and their gliding characteristics were compared.[Results] Significant differences were found among the four regions. In particular, the gastrocnemius (both shallow and deep layers) and the soleus showed significantly greater lateral displacement compared to the fat layer. Moreover, a significant difference was observed in gliding distance between DF and DIF, suggesting that EA markedly influences the lateral dynamics of muscle and fascial tissues.[Discussion] This study represents the first objective visualization of muscle contraction dynamics induced by EA. These findings may contribute to the establishment of appropriate application methods and treatment strategies for EA. Future studies involving different muscle groups and stimulation parameters are expected to further expand its clinical applications.

The purpose of this study was to determine the developmental pattern of swing speed in youth baseball players between 6 and 14 years old. A total of 1213 baseball players performed toss batting. Swing speed was measured with a specialized accelerometer. In addition, 618 of the 1213 players were measured for total fat free mass by using Inbody770. In study1, Regression analysis was performed on the relationship between chronological age or height and swing speed, and the extreme values were calculated. Then, an allometric equation based on height was also used to estimate the relative growth of swing speed and total fat free mass and to compare the difference of relative growth patterns between swing speed and total fat free mass in study2. Swing speed was strongly related to both chronological age and height, with cubic regression for the relationship with chronological age and linear for the relationship with height. The regression equation obtained for chronological age was solved and found that developmental rate was maximal at approximately 10.25 years old. Allometric analysis showed that the developmental pattern of swing speed differed from that of fat free mass, with a temporary decline in developmental rate from 153.6 cm to 160.9 cm. Based on the results of this study, further research in youth baseball players would be expected to identify the factors causing sluggish development of swing speed as well as to develop an exercise program for improving batting ability.