Development pattern of swing speed of batting in youth baseball players / 体力科学

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.

Local Sagittal Alignment of the Lumbar Spine and Range of Motion in 627 Asymptomatic Subjects: Age-Related Changes and Sex-Based Differences

STUDY DESIGN: Prospective cohort imaging study. PURPOSE: This study aimed to evaluate lumbar sagittal alignment and range of motion (ROM) using radiographs in a large asymptomatic cohort and identify sex-based differences and age-related changes in the subjects. OVERVIEW OF LITERATURE: Several researchers have tried to establish normal alignment and kinematic behavior of the lumbar spine, using plain radiographs. Few studies have employed a large and sex-and age-balanced cohort. METHODS: Total 627 healthy volunteers (at least 50 males and 50 females in each age decade, from the 3rd to the 8th decade) underwent whole spine radiography in the standing position; lumbar spine radiography was performed for all subjects in the recumbent position. Lumbar lordosis (LL, T12–S1) and ROM during flexion and extension were measured using a computer digitizer. RESULTS: The mean LL was 36.8°±13.2° in the recumbent position and 49.8°±11.2° in the standing position. The LL was greater in the standing position than in the recumbent position; further, LL was higher in females as compared to that in males. Local lordosis at each disk level increased incrementally with distal progression through the lumbar spine in both the positions. Local lordosis at L4–S1 was 29.8°±8.0° in the recumbent position and 34.2°±8.3° in the standing position and occupied 85.1% and 70.8% of the total LL, respectively. However, local lordosis in the standing position decreased with age at L2–3, L3–4, and L4–5 levels. Total lumbar ROM (T12–S1) decreased with age. The ROM in females was higher than that in males. CONCLUSIONS: We established the standard value and age-related changes in the lumbar alignment and ROM in each age decade in asymptomatic subjects. These data will be useful and provide the normal values for comparison in clinical practice to identify sex-based differences and age-related changes.

A Morphologic Study of the Structural Changes of Normal Aging Facial Skin

In an attempt to elucidate the morphologic changes of normal aging skin, the present study was undertaken in human facial and chest well skin of individuals aged from 4 months to 76 years old. Biopsied skin was studied with light microscope, scanning electron microscope, and transmission electron microscope, using both conventional and tannic acid staining. The morphologic changes in the skin were noted as follow: 1. Structurally, the aged epidermis gradually became somewhat thinner, with flattening of the dermoepidermal interface. The number of melanocytes also decreased. 2. Abnormalities of elastic fibers such as loss of oxytalan fibers were observed from age 30. It was the initial sign of the aging process of elastic fibers, followed by abnormal changes in elaunin and mature elastic fibers. The degree of facial skin abnormality was rather more severe than that of the chest wall skin. 3. In individuals more than 50 years old, the age related changes in mature elastic fibers were more severe. Transmission electron microscopically, the electron density in elastin was irregular. The elastic fibers also showed pores and irregular splitting with fragmentation. Fine granular materials were scattered near the elastin. 4. Scanning electron microscopically, the elastic fibers in young adult skin showd ribbon-like fibers aligned in the same direction. They were either cylindrical or elliptical, having smooth surface. In old skin, the elastic fibers ran in various directions, forming complicated networks. These were larger, more elliptical and more branched than those in young adult skin. In summary, histologic changes of aging are much more prominent in sun-exposed skin(facial skin) than in sun protected skin(chest wall skin). A completely different spectrum of elastic fiber abnormalities was found in individuals more than 30 years old. The result indicates that elastic fiber abnormalities are related to aging skin.