Whole-body reaction time is used as a measure of athletic ability in preschool children. The purpose of this study was to compare whole-body reaction time in preschool children in relation to leg extensor muscle strength. The participants were 198 preschool children aged 3 to 6 years, who underwent assessment of whole-body reaction time and isometric right leg extensor muscle strength. Whole-body reaction time (T4) was fractionated into movement start time (T1) , counter movement time (T2) , motor time (T3) . There was a significant difference between each age for T1 (p < 0.001) , T3 (p < 0.01) and T4 (p < 0.001) . However, there was no significant difference in time of T2. There was correlation between whole-body reaction time and leg extensor muscle strength. The measurement of T1 led to assessment of the development of the brain and nervous system. And we made a proposal that the difference of exercise experience might influence the result for the measurement of T4.

The purpose of this study was to examine the relationship between the levels of proficiency in the straddle and achievement in the squat vault in vaulting box exercise of elementary school children. Participants comprised 239 children (114 boys, 125 girls) in the 5th and 6th grades, each performing straddle and squat vaults while their movements were observed and videotaped from the left and front. The movements of the former were assessed using the observation criterion and proficiency identified through Latent Class Analysis. The level of achievement in the latter was evaluated over three stages: “can jump stably until landing (A),” “can jump over (B),” and “cannot jump over (C).” To determine whether achievement of the squat vault depended on proficiency in the straddle vault, a chi-squared (χ2) test was performed; if a significant difference existed, a residual analysis was conducted.
The conclusions of this research were as follows:
1．If the movements in the straddle vault consist of a weak takeoff and reliance on the arms to jump over the box, then the squat vault is difficult to achieve.
2．If the movements in the straddle vault are stable until landing, then stability is easily achieved in the squat vault.

It is well known that Japanese children have severe sleep problems and circadian misalignment. Many studies have found that sleep problems and circadian misalignment in children lead to not only increases in diurnal sleepiness and impairment in memory function, but also behavioral problems, long-term absentee, and suicidality. It has been reported that children who participate in a long-term camp exhibit improved melatonin secretion patterns. However, the factors that contribute to the improvement in melatonin secretion patterns during a long-term camp are unclear. Therefore, the purpose of the present study was to examine the living situations related to melatonin secretion patterns in free-living children. Forty-four 5th-grade children in an elementary school (22 boys and 22 girls) participated in the present study. Saliva melatonin was collected at 21 : 30 (night) and 6 : 30 (morning) at home. Based on night and morning saliva melatonin concentrations, we divided the participants with night > morning to the “morning-type group” and those with night ≤ morning to the “night-type group.” All participants completed a self-administered questionnaire consisting of items to obtain living situations information including physical activity, diurnal light exposure, dim light environment, use of electronic devices, and internet addiction disorder. As a result of the present study, children classified as the night-type group based on night and morning saliva melatonin concentrations showed a higher percentage than the morning-type group (72.7％, n＝32 and 27.3％, n＝12, respectively; p < 0.05). In addition, the total physical activity duration in a day in the morning-type group was significantly about 56％ longer than that in the night-type group [146.7±83.4 min and 94.2±63.3 min (mean±standard deviation), respectively; p < 0.05]. However, there was no association among melatonin secretion patterns and other living situations (diurnal light exposure, dim light environment, use of electronic devices, and internet addiction disorder). Our findings suggest that the living situation that is related to melatonin secretion patterns in free-living children is total physical activity duration in a day.