The International Physical Activity Questionnaire (IPAQ) is a self-reported questionnaire for assessment of physical activity and has been validated in many countries among adults. However, there are few studies about the validity of IPAQ for children. The purpose of this study was to investigate the validity of moderate to vigorous physical activity according to the modified version the IPAQ for Japanese Early Adolescents (IPAQ-JEA). Ninety-two adolescents aged 10-13 years participated in this study. The validity of the IPAQ-JEA criteria was tested using an activity monitor (Active style Pro, HJA-350IT; ASP). Daily physical activity was continuously monitored for one week by ASP. The participants were asked to complete the IPAQ-JEA after wearing the ASP. The epoch length of ASP was set at 1-min in this study (ASP_1-min). According to the minute by minute METs values, time spent on moderate intensity physical activity (MPA, 3 to 6 METs), vigorous intensity PA (VPA, > 6 METs), and moderate to vigorous intensity PA (MVPA, > 3 METs) was calculated. In addition, we also calculated bout physical activity maintained for 10 minutes or longer (ASP_bout). Weekly time spent on MVPA assessed by IPAQ-JEA (MVPA_IPAQ-JEA) was significantly correlated with that assessed by ASP_bout (MVPA_ASP_bout) (ρ=0.359, p<0.01) and ASP_1-min (MVPA_ASP_1-min) (ρ=0.399, p<0.01). However, MVPA_IPAQ-JEA was significantly higher than that of MVPA_ASP_bout and MVPA_ASP_1-min (p<0.001). Although time spent on VPA assessed by IPAQ-JEA (VPA_IPAQ-JEA) was also significantly correlated with that assessed by ASP_bout (VPA_ASP_bout) (ρ=254, p<0.05) and ASP_1-min (VPA_ASP_1-min) (ρ=438, p<0.01), time spent on VPA_IPAQ-JEA was significantly higher than that for VPA_ASP_bout and VPA_ASP_1-min (p<0.001). These results support the use of the IPAQ-JEA as a relative measure of physical activity among 10-13-year-old children.

The purpose of this study was to examine the relationships between patterns of daily physical activities measured by accelerometer and physical activity level (PAL) in children. Firstly, activity intensities during incremental exercise were measured using a tri-axial accelerometer (HJA-350IT) in twenty one children aged 10.6 ± 0.9 years. As a result of receiver-operating characteristic curve analysis, the cut-off value for discrimination between walking and running activity was set at 7.2 METs of HJA-350IT. Secondly, total energy expenditure (TEE) in daily life was measured by doubly labeled water method, and durations of lifestyle, walking, and running activities were measured by the accelerometer in 6^th grade elementary school children (11 boys and 10 girls). TEE and physical activity level (PAL) were 2,021 ± 343 kcal/day and 1.56 ± 0.17, respectively. The average durations of lifestyle, walking and running activities were 188 ± 30 min/day (50.6 ± 6.0 %), 171±28 min/day (45.9 ± 5.0 %) and 13.3 ± 7.6 min/day (3.5 ± 1.8 %), respectively. The proportion of the duration of running activity was positively correlated with PAL (r = 0.615, p < 0.01), and the proportion of the duration of lifestyle activity was negatively correlated with PAL (r = -0.439, p < 0.05). There was no relationship between the proportion of the duration of walking activity and PAL (r = 0.300, n.s.). These results suggest that running activity is important to increase PAL more than ever in primary school children.

A study was performed to clarify the relationships between oxygen uptake (VO₂) kinetics on recovery from incremental maximal exercise and blood lactate, glucose and alanine metabolism. Eight healthy males aged 21.6±3.3 years were studied. The incremental exercise test was performed using a modified version of Bruce's protocol until 30 min after exhaustion. The VO₂ responses on recovery were fitted by a two-component exponential model. Blood lactate concentration in the recovery phase was fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (γ2) expressing the rate of blood lactate removal. Both blood lactate and plasma alanine concentration were significantly increased from rest to maximal exercise, and were significantly decreased thereafter, but remained above resting values for 30 min after the maximal stage. Blood glucose concentration was significantly decreased following maximal exercise and returned to the pre-exercise value by 30 min after the maximal stage. Concentrations of plasma branched-chain amino acids (valine, leucine and isoleucine) were significantly decreased from the maximal stage until 30 min after exhaustion. The time constant of the slow component on recovery VO₂ [τVO₂ (s) ] was correlated with neither γ2 nor the degree of change in blood lactate from the maximal stage until 30 min after exhaustion (Δlactate) . However, τVO₂ (s) was significantly correlated with both Δ blood glucose and Δ alanine. In addition, Δ alanine was significantly correlated with Δ blood glucose. From these results, we conclude that oxygen uptake kinetics after exhaustive maximal exercise is related to glucose resynthesis through alanine metabolism, as compared with that from lactate metabolism.

A study was performed to clarify the effects of endurance training above the anaerobic threshold (AT) on the isocapnic buffering phase during incremental exercise in athletes. Eight middle-distance runners aged 19.6±1.2 years performed incremental exercise testing with a modified version of Bruce's protocol. After a 6-month high-intensity interval and paced running training at levels above AT, maximal oxygen uptake (VO₂max) (ml⋅ kg^-1⋅min^-1) was significantly increased from 60.1±5.7 to 64.7±5.5 (p<0.05) . AT (m⋅lkg^-1⋅min^-1) was slightly but significantly increased from 28.2±3.5 to 29.6±4.3 (p<0.05) . The respiratory compensation point (RC) (ml⋅ kg^-1⋅min^-1) was markedly increased from 53.0±8.3 to 57.7±8.2 (p<0.05) . Although neither the slope of the first regression line below AT (S1) nor that of the second line above AT (S2) calculated by V-slope analysis was altered, the range of isocapnic buffering (ml⋅kg^-1⋅min^-1) from AT to RC was significantly extended from 24.8±5.9 to 28.1±6.0 after the 6-months of training (p<0.05) . In addition, the amount of change in VO₂max after the 6-month of training period (ΔVO₂max) was correlated with Δisocapnic buffering (R=0.72, p<0.05) . We conclude that the degree of increased respiratory compensation point is larger than that of AT after high-intensity endurance training at levels above AT, and that the range of isocapnic buffering may be an important factor in relation to the increase in the maximal aerobic capacity of athletes.

A study was conducted to establish a method for quantitative evaluation of both the rate and degree of muscle oxygenation during ramp exercise using Near Infrared Spectroscopy (NIRS), and to determine the relationship of the indices to body composition and physical fitness. The subjects were 13 healthy men. After a warm-up period of 3 min at 20-W, the ramp exercise test was conducted. The exercise consisted of an increasing work rate at a slope of 20 W/min on a cycle ergometer performed until volitional fatigue. The NIRS probe used in the cycling exercise was placed on the vastus lateralis muscle. After 30 min of exercise, calibration was performed by cuff occlusion for 10 min with a pressure of 260 mmHg for quantitative determination of the NIRS curve. The oxygenation curve measured by NIRS during the exercise initially exhibited a linear decrease as the work rate increased. This rate of decrease in oxygenation was indicated by the NIRS slope (%/W) obtained from the calibration curve. In later stages of the exercise, the NIRS curve became flattened with increased work rate. The breaking point between the sloping phase and the flat phase was named the “NIRS Threshold 2, NT 2”. In addition, the rate of decrease in oxygenation at the end of exercise per maximal NIRS decrease obtained from the calibration curve was indicated as the %NIRS fall. The mean NIRS slope and %NIRS fall were 0.3±0.1%/W (range, 0.13 to 0.50%/W) and 29.9±11.8% (range, 12.0 to 50.0%), respectively. NT 2 was observed in 8 of the 13 subjects. The subjects were divided into two groups (NT 2 (+) and NT 2 (-) ) based on the appearance of NT 2. Both the NIRS slope and %NIRS fall in the NT 2 (+) group were significantly higher than those in the NT 2 (-) group. The NIRS slope was significantly correlated with VO₂/wt at VT (r=0.73, p<0.05) and wattage at VT (r=0.86, p<0.0001) . The %NIRS fall was significantly correlated with VO₂/wt at peak (r=0.80, P<0.001) . The NIRS slope and %NIRS fall were not significantly correlated with body mass index, %fat or thigh circumference.
These findings suggest that the NIRS slope indicates the efficiency of oxygen exchange in muscles activated during incremental exercise, and that the %NIRS fall indicates the ability to utilize Oxy-Hb+Mb against maximal oxygenation capacity in muscles. The NIRS slope and %NIRS fall can therefore be used as indices of muscular limitation during exercise, and as indices of muscular adaptation during exercise.

The purpose of this study was to confirm both the reproducibility of indices (NIRS slope, NT2, %NIRS fall) and the specificity obtained by analyzing the muscle oxygenation curve measured by near-infrared spectroscopy (NIRS) during ramp exercise. Ten healthy men participated in this study. The NIRS probe was placed on the vastus lateralis muscle. An increase in oxygenation was observed from rest to warm-up at 0 watts (Δ NIRS) . Oxygenation began to decrease lineally as the workload increased (NIRS slope) . In the latter phase of exercise, the oxygenation curve flattened out despite an increasing workload, and as a result, an inflection point was formed (NT2) . The minimum value of oxygenation during ramp exercise was indicated as“%NIRS fall.”
Protocol 1. After a warm-up period of 3 min at 0 watts, a ramp exercise (20 watt/min) test was performed until volitional fatigue. The test was performed for each subject twice (test-1, test-2) with a 1-week interval. Protocol 2. A test was performed with three consecutive ramp exercises (lOwatt/min·20watt/min·30watt/min) up to120watt each with sufficient rest between the exercises.
NT2 was observed in 7 of 10 subjects. Test-1 and test-2 mean values of ANIRS, NIRS slope, watts at NT2 (NT2) and %NIRS fall were not significantly different, and the correlations between test-1 and test-2 were highly significant (r=0.94, P<0.0001: ANIRS, r=0.99, P<0.0001: NIRS slope, r=0.91, P<0.002: NT2 and r=0.78, P<0.005 : %NIRS fall) . The regression lines obtained for correlations of results of test-1 and test-2 were y=-5.89+1.38X (Δ NIRS), y=0.02+ 1.03X (NIRS slope), y=31.52+0.83X (NT2), and y=19.91+0.61X (%NIRS fall) . No significant differences in both intercept and coefficient between the regression line and identity line were found in the NIRS slope and NT2. The rate of decrease in the oxygenation curve became steeper with an increase in work-load from 10 watts/min to 20 watts/min and to 30 watts/min. However, the mean values of the NIRS slope, modified by watts, were 0.29±0.06%/watt, 0.29±0.07%/watt and 0.29±0.07%/watt, respectively. There were no significant differences of the NIRS slopes among these exercises. The results indicate constancy of the rate of decrease in oxygenation per workload.
In conclusion, these findings demonstrate the reproducibility of the NIRS slope and the appearance of NT2 during ramp exercise, and the specific way in which the decrease in muscle oxygenation reflects workload. They suggest that analysis of the muscle oxygenation curve can be used to estimate muscular metabolism and indices of training effects.

The purpose of the present study was to develop a new method that enables individualized determination of the optimal exercise intensity for health promotion. Our study was based on the following observations : (1) physical activity at ventilatory threshold (VT) has been useful for enhancing physical fitness and even improving medical conditions such as heart failure, hypertension and diabetes, (2) exercise intensity at VT is characterized by suppressed vagal activity, and (3) vagal activity can be evaluated by analyzing heart rate variability (HRV) . In the first study we defined a criteria for determining the exercise intensity corresponding to VT using HRV analysis (heart rate variability threshold, THRV) . In 16 normal subjects, a time series of ECG RR interval were recorded and the means of the sum of the squared differences in successive RR intervals (MSSDs) were calcu-lated during a ramp exercise test with a cycle ergometer. Based on the values of MSSD and the dif-ferences in successive MSSDs (ΔMSSD) at the intensity of VT, we defined the criteria of THRV as follows : MSSD<25 msec²and ΔMSSD<6 msec². Another exercise test with a cycle ergo-meter was performed to evaluate the relationship between THRV and VT in 63 normal subjects. Heart rate (HR) and oxygen uptake (VO₂/wt) at THRV were 111.8±13.2 beats/min and 15.2±4.4 ml/kg/min, and HR and VO₂/wt at VT were 116.2±11.6beats/min and 16.5±3.7ml/kg/min, respectively. There was a significant correlation between THRV and VT (HR : r=0.82, p<0.001, VO₂/wt : r=0.88, p< 0.001) . Thus, THRV and VT provided almost identical exercise intensities. As a result, we propose that, similar to VT, THRV can be used as an indicator of the optimal exercise intensity suitable for health promotion in normal subjects.

The purpose of this study was to determine daily steps corresponding to the reference value for the quantity of Physical Activity and Exercise for Health Promotion 2006 (23 METs·h/wk) considering non-locomotive activities. Two hundred and thirty one men and 224 women wore a tri-axial accelerometer for two weeks. We analyzed the data in each age group (young (less than 40 years), middle-aged (40 to 59 years), and elderly (60 years or more) groups), also. There were significant relationships between daily steps and locomotive activity (r = 0.762 to 0.820, p < 0.001) and total (locomotive and non-locomotive) physical activity (r = 0.706 to 0.824, p < 0.001) with intensity of 3 METs or more in all groups. The daily steps corresponding to 23 METs·h/wk, calculated using regression lines between the daily steps and total physical activities with intensity of 3 METs or more in men and women were 6,534 steps/d and 6,119 steps/d. On the other hand, the daily steps corresponding to 23 METs·h/wk, calculated using regression lines between the daily steps and locomotive activities with intensity of 3 METs or more in men and women were 7,888 steps/d and 8,584 steps/d. These results suggest that non-locomotive activity should also be taken into consideration in the case of assessment of a daily physical activity.