This study was conducted to elucidate the characteristics of children who were born later in the school year, exhibiting better physical fitness. The subjects were 1202 public elementary school children (grades 1-6) in Ibaraki prefecture, for whom birth date, height, weight, physical fitness test scores, and physical activity had been assessed by questionnaire. They were divided into four categories by birth date：Q1, April-June；Q2, July-September；Q3, October-December；and Q4, January-March (including April first). All data were integrated after classification by grade and gender. Physical fitness groups were defined to include subjects who had more than 50 physical fitness deviation score as a higher physical fitness group (HPF). The others were a lower physical fitness group (LPF). Results of statistical analysis show for Q4 that physical activity of HPF had a higher value than LPF, although no difference was found for height or BMI. For HPF, a lower value was found for height of Q4 than for either Q1 or Q2, although no difference was found for BMI or physical activity. These results demonstrate that although elementary school children who were born later in the school year and who had higher physical fitness showed poor body size, they attained higher physical fitness through higher levels of physical activity.

Low birth weight has been associated with lower levels of physical activity in later life as assessed by questionnaires. Earlier infant motor development was also recently shown to be an early predictor of physical activity as indicated by an increased frequency of sports participation during adolescence. The aim of the present study was to determine the associations between birth weight plus the timing of infant motor development and moderate to vigorous physical activity in children. The subjects were 379 elementary school children aged 6-12 years. The children's current weight and height were evaluated, and their birth weight and the age when the child first walked unassisted were reported based on their parent's memory. The children's physical activity was objectively measured using accelerometry（Active style Pro HJA-350IT, OMRON). The time（min／day）spent in moderate to vigorous physical activity（Metabolic equivalents［METs] ≥3）was derived from the accelerometry data. Our analyses revealed that the children's age at walking unassisted was inversely correlated with the time spent in moderate to vigorous physical activity（r＝ .0.24）when controlled for gender and current age. A multiple linear regression analysis revealed that later age at walking unassisted was significantly associated with decreased time spent in moderate to vigorous physical activity（B＝-2.28, p＜0.001), independent of gender, current age, body weight, and wearing time. There was no evidence of an association between birth weight and moderate to vigorous physical activity. The present findings indicate that delayed infant motor development, in terms of age at walking unassisted, may predict lower levels of physical activity in children. Appropriate interventions to prevent physical inactivity may be needed for infants with slower motor development.

This study examined how the size of playground in the nursery school is related to children's levels of physical activity in playing outdoor (in the playground and outside of the school). We compared two nursery schools, School A with a smaller playground and School B with a larger playground. A total of 42 children (20 children from School A；22 children from School B) participated.

We observed children's outdoor play for ten days in the morning and measured physical activity levels by accelerometer. We found the following：

(1) that the activity level of children at School A with a smaller playground was lower than that of children at School B with a larger playground, and

(2) that outside-of-the-school outdoor play is associated with higher activity levels than outdoor play in the school playground, however,

(3) that both schools did outside-of-the-school outdoor play only once during the two week observation period.

Given the vital importance of providing children with enough outdoor play, we must address playground size and use of outside-of-the-school outdoor play.

The purpose of this study was to clarify the biological maturity of top junior baseball players in relation to Peak height velocity (PHV) ages and birth month. The subjects were 25 junior high schools (TOP) with high competition level and 30 standard baseball players （BB）. Using the proportional distribution method, the PHV age was calculated as an index of biological maturity. Consequently, the PHV age of TOP group （12.3± 0.7 years） was significantly lower than the BB group （13.0±0.8 years）. The birth month distribution was different between the two groups. 84％ of the TOP group and 56％ of BB group were born between April and December, suggesting that TOP group matures earlier than the BB group by 0.9 years.

The aim of this study was to clarify the grip strength and progress of development in infants aged 0 to 2 years old. The subjects were 396 infants and we measured their grip strength with grip dynamometer （T. K. K. 1269r） for the infants. Date on 313 subjects out of the 396 were analyzed. The average of grip strength was followed：0 to 5 months was 0.81 kg, 6 to 11 months was 1.05 kg, 12 to 17 months was 1.45 kg, 18 to 23 months was 1.72 kg, 24 to 29 months was 2.31 kg and 30 to 35 months was 3.00 kg. Significant difference between boys and girls were not shown. The relationships between grip strength and age was the most significant, then height and weight next to age. Grip strength increased with age, as a result, we were able to draw the growth diagrams for grip development in infants aged 0 to 2 years old.

The purpose of this study was to examine the longitudinal developmental process of the “foresee-movement” in young children（3-4 year and 4-5 year old）over the period of two years. Forty-five young children participated in this study and completed a parabolic-line task. In this task, an experimenter threw the ball to a height of about 1.6 m from the floor toward a drop point 2 m in front of the participant. The participant was told to move forward 1 m and catch the ball after the first bounce. The participants' catching movements were video recorded from the right. The catching movement was classified into six patterns：（1） no movement；（2）the ball bounced once and passed over the head；（3）the ball was caught after two bounces；（4）an attempt was made to catch the ball after one bounce, but the ball could not be touched；（5） an attempt was made to catch the ball after one bounce, but the ball was knocked away；and（6）the ball was caught after one bounce.

As a result, the catching rate increased with age. “Total motion time” and “Movement time” shortened with participant's age. The movement-patterns of the 3 and 4-year-old children were classified into Patterns 1-3. Many of the movement-patterns among the 5-year-old children, on the other hand, were classified as Pattern 5. Motion-Pattern 6 increased significantly between the ages of 4 and 5.

Obviously, young children are able to increasingly anticipate the track of the ball and estimate their own movements as they age. Foresee-movement gradually develops with age, even if the catching movement is classified as a failure.

This study aimed to provide a basis for the provision of appropriate guidance by clarifying the characteristics of development of gliding motions and flutter kicks as basic swimming techniques, involving second-（28）and fourth-（18）grade elementary school children. The experiment was conducted using a radio-camera for comprehensive underwater and water-surface recording（60 fps). Recorded gliding motions were classified into 3 patterns：Ⅰ（31）：kicking off the wall with both legs while maintaining both arms pointing forward；Ⅱ（14）：kicking off the wall with one leg while maintaining both arms pointing forward；and Ⅲ（1）：kicking off the wall with one leg while maintaining both arms pointing backward. Similarly, recorded flutter kicks were classified into 2 patterns：Ⅰ（43）：maintaining both arms pointing backward；and Ⅱ（3）：maintaining both arms pointing forward. The initial and mean velocities when adopting the streamline form were the highest in pattern Ⅲ, which was followed by Ⅱ and Ⅰ, in this order. In each pattern, the values were higher among fourth than second graders, suggesting that preparatory movements before and the streamline position after kicking had been mastered within the period between the second and fourth grades. On the other hand, regarding flutter kicks（pattern Ⅰ), there were no significant differences in the distance or mean velocity between second and fourth graders, or changes indicating improvements in these movements were not observed.