The purpose of this study was to assess daily physical activity and time spent on activities of various intensities, and to examine the relationship between daily physical activity and physical fitness in junior high school students. The subjects were 314 junior high school students (135 boys, 179 girls, 14.0±0.1 years). Daily physical activity was evaluated using accelerometers that they wore around the waist for 10 days. The accelerometers calculated steps and time spent on activities of vigorous intensity (LC7-9: higher intensity than brisk walking). A physical fitness test (8 items) was employed to evaluate the fitness of pupils. The total accelerometer steps (counts/day) were 13772±4764 for boys and 11209±2636 for girls on weekdays, and 8311±4743 for boys and 7159±3338 for girls on weekends, respectively. On weekdays, time spent on activities with an intensity of LC7-9 (minutes/day) was 18±17 for boys and 11±7 for girls. Positive associations were found between physical fitness and daily physical activities in the case of many items. The fitness test score was significantly more highly correlated with LC7-9 than with LC1-6 in boys and girls. In the case of eighth graders, in order to reach a score of B in the physical fitness test, it was suggested that the total steps and time spent on activities with an intensity of LC7-9 may be needed at least 13000 steps and 20 minutes in boys, and 10000 steps and 10 minutes in girls, respectively.

The purpose of this study was to investigate the association between activity levels assessed by a uniaxial accelerometer and metabolic equivalents (METs) during walking and running in school students. The participants were elementary (10 boys, 10.3 ± 0.8 years), middle (10 boys, 13.0 ± 0.9 years) and high school students (10 boys, 15.7 ± 0.7 years) who performed treadmill walking (1, 3, and 5 km/h respectively) and running (5, 7, and 9 km/h respectively) trials. Activity levels were assessed using a uniaxial accelerometer (Lifecorder EX; Suzuken Co. Ltd., Nagoya, Japan). Energy expenditure was measured by indirect calorimetry. METs and activity levels indicated by Lifecorder were highly correlated in elementary (y = 0.0432x² + 0.0914x + 1.786, r = 0.883, p < 0.05), middle (y = 0.0781x² - 0.0262x + 2.1098, r = 0.913, p < 0.05), and high (y = 0.0516x² + 0.1863x + 1.7812, r = 0.876, p < 0.05) school students. We confirmed that higher accuracy showed LC5, LC4, and LC4 for elementary, middle, and high school students, respectively. In conclusion, this study suggests that Lifecorder intensity for ≥3 METs physical activity indicate ≥5, ≥4, and ≥4 for elementary, middle, and high school students, respectively.

Very few studies have reported an independent association of the physical activity-related indices with the psychological stress reaction. The present study therefore investigated the association of fitness and screentime as one of the indices of sedentary behavior with the four types of psychological stress reactions and the number of days absent from school for 249 children at a local public school and a metropolitan private school while considering confounding factors. No significant difference was observed in the fitness level of both schools; however, the rate of obesity, the screentime and the level of all psychological stress reactions were significantly worse in the public school. Further, significant differences and trends among the groups classified by fitness level were recognized in the rates of participation in after school activities, feeling of powerlessness and days of absence per year. In addition, the odds ratio of the screentime for depressive and anxiety symptoms was 1.004 (95%CI: 1.000-1.007, p=0.039), while the odds of the fitness level for high feeling of powerlessness and more than five days of absence were 1.582 (95%CI: 1.045-2.396, p=0.030) and 1.434 (95%CI: 1.045-2.396, p=0.015), respectively, after adjusting for the school type, differences in lifestyle and participation in after school activities. In conclusion, the fitness level and the screentime were associated with high psychological stress reactions and the days of absence, independent of the above-mentioned adjusting factors among the children in the present study. Prospective and interventional studies to verify these results are needed.

The purpose of present study was to examine validity of pedometer with accelerometer (Lifecorder-EX ; LC) and to assess the daily physical activity (PA) of Japanese junior high school students by LC method. Firstly, to examine validity of LC, ten students (13.6±0.5 years old) wearing LC on their waists performed the walking and running tests. Energy expenditure was measured by the expired gas analysis method during the tests. The results showed that the activity level of LC had a high correlation with the exercise intensity (VO₂ : r=0.948, METs : r=0.931), and it was from 7 to 9 (LC7－9) in the more intense activity than running. Secondly, PA of 206 boys and 220 girls aged 12－15 years were measured using LC. Step counts and activity time of LC7－9 each were 9500－15000 counts and 10－19 minutes on weekdays, and 6500－10000 counts and 5－12 minutes on weekends. PA analyzed by MANOVA were lower on weekends than on weekdays, and decreased in proportion as grade, and that of boys were significantly higher than that of girls. Present study suggests that LC method is a good way of measuring PA for junior high school students in free-living condition.

The purpose of this study was to assess daily physical activity and time spent on activities of various intensities, and to examine the relationship between daily physical activity and physical fitness in elementary school children. Subjects were 288 elementary school children (140 boys, 148 girls, 9.6±0.5 years). Daily physical activity was evaluated by accelerometers, worn around the waist for 10 days. Accelerometers calculated steps and vigorous intensity time (LC7-9: higher intensity than brisk walking). A physical fitness test (8 items) was applied to evaluate fitness in pupils. Total accelerometer steps (counts/day) were 18333±3869 for boys and 13957±2970 for girls on weekdays, and 11932±4827 for boys and 9767±4542 for girls on weekends, respectively. Time spent in LC7-9 (minutes/day) was 31±12 for boys and 20±7 for girls on weekdays. Positive associations were found between physical fitness and daily physical activities for many items. Above all, there was a relatively strong correlation between aerobic capacity and LC7-9 time. On the other hand, the correlations were low among girls. For fourth graders, in order to reach a B rank score in the physical fitness test, it was suggested that the total steps and LC7-9 time required at least 17000 steps, 30 minutes in boys, and 13000 steps, 20 minutes in girls, respectively.

This study was carried out to compare the nutrient intake, urinary excretion of mineral (Na, K, Ca, Mg, Zn, Fe, Cu ), and the ratios of creatinine (Cr), body mass index (BMI) and basal metabolic rate (BMR) to the amount of mineral in 24-hour urine between both the male university students with few exercise (non-exercisers) and male university distance runners. The propriety of ratios of Cr, BMI and BMR was also examined in order to estimate intake of mineral for the male university distance runners.
There were no significant differences in the intakes of energy, protein and carbohydrate between the both groups of subjects, and those major nutrients were at reasonable levels for the both groups of subjects. On the other hand, neither the intake levels of VB₆, Ca, Mg, and Cu in the non-exercisers, nor niacin, Mg and Cu in the male university distance runners reached the level of Recommended Dietary Allowance for the Japanese. The intakes of retinol, VB₁, VB₆ and Ca were higher in the male university distance runners than in the non-exercisers. The urinary excretion and excretion ratio to intake of Zn, excretion ratio of Na, ratios of Cr, BMI and BMR of Zn, and Cr ratio of Na were higher in the non-exercisers than those in the male university distance runners. So as to achieve the same levels of Cr ratios of Ca and Zn as the non-exercisers, the male university long distance runners should take larger amounts of those minerals than the non-exercisers. It was suggested that the ratio of BMR rather than that of Cr ratio to urinary excretion of mineral would be suitable for the estimation of a desirable intake level of mineral for the male university distance runners.

The purposes of this study were to investigate the relationships between physical activity variables and physical fitness, and between amount and intensity of physical activity in children and adolescents. Subjects were divided into two groups : 178 children (99 boys aged 9.8±0.6 and 79 girls aged 9.7±0.6) who had not reached the age of peak height velocity (PHV), and 336 adolescents (141 boys aged 15.0±1.1 and 195 girls aged 15.3±1.2) who had reached the age of PHV. Physical activity level (PAL : total energy expenditure/basal metabolic rate) which indicates the amount of physical activity, and time engaged in each of physical activity intensity (light, moderate and vigorous), which indicates the intensity of physical activity were estimated from uni-axial accelerometer. Physical activity was monitored for 3 consecutives days : 2 weekday and 1 weekend day. Moreover, physical fitness test suggested by the Ministry of Education, Culture, Sports, Science and Technology was applied. Results of this study showed that PAL was closely related to physical fitness in children, while time engaged in vigorous activity was more related to physical fitness in adolescents. On the other hand, time engaged in light and moderate activity was closely associated with PAL in younger girls, whereas in younger boys, PAL was closely related to time engaged in moderate and vigorous activity. However, time engaged in moderate activity was more related to PAL in the adolescent group. These results suggest that the relationship between physical activity variables and physical fitness and between amount and intensity of physical activity might vary according to the growth development of boys and girls respectively.

The purpose of this study was to assess physical activity using questionnaires and an accelerometer in 4th grade children (aged 9-10 years) and compare differences between the methods of evaluation. Fourth elementary school children were selected (total = 221), including 106 boys and 115 girls. The participants were investigated on their anthropometry and physical activity. The questionnaire was used to evaluate exercise time and the accelerometer was used to measure moderate-to-vigorous physical activity (MVPA). During weekdays and weekdays, the exercise time was significantly higher than MVPA for girls. For boys, the exercise time was significantly higher than MVPA only on the weekends. As a result of Bland–Altman analysis, for both boys and girls in weekday and weekends, mean of questionnaire and accelerometer was associated with difference of questionnaire and accelerometer (Boys in weekday, r = 0.777, p < 0.001; Boys in weekends, r = 0.964, p < 0.001; Girls in weekday, r = 0.731, p < 0.001; Girls in weekends, r = 0.937, p < 0.001). In conclusion, our results suggested that a questionnaire-based evaluation of exercise time shows significant difference compared with accelerometer-based measurement of MVPA. In addition, exercise time of questionnaire-based evaluation was higher than MVPA of accelerometer-based measurement for both boys and girls on all days.