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.

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.

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.

The purpose of present study was to examine validity of accelerometer (Lifecorder ; LC) and to assess the free-living physical activity (PA) in Japanese elementary school students used by LC method. Firstly, to examine validity of LC, twelve children, aged 11.2±1.0 years, were measured total energy expenditure (TEE) by doubly labeled water method and resting energy expenditure (REE) by the expired gas analysis. Physical activity energy expenditure (PAEE) is calculated as 0.9 TEE minus REE. At the same time, PA was evaluated by both daily walk count (WC) and vigorous activity time (LC7-9) using LC method. PAEE per 1 kg body weight significantly correlated with WC (r=0.785, p<0.005) and LC7-9 (r=0.828, p<0.001). Secondly, 140 boys and 167 girls, aged 8-11 years were measured PA by LC method. WC and LC7-9 each were 13000-18000 counts and 16-32 minutes in week-day, and 8000-12500 counts and 8-18 minutes in week-end. PA analyzed by MANOVA were significantly higher in boys than in girls, and lower in week-end than in week-day, and decreased in proportion as grade. Present study suggests that LC method is a good measure of PA in free-living condition for elementary school students.