This study examines the effects of physical fitness level and exercise habits on subjective fatigue symptoms in adolescents. 746 young male adults (age: 16.5 +/- 1.0 year, 15-20 years) participated in the physical fitness tests (grip strength, sit-up, trunk anteflexion, repeated sideways jump, 20-meter shuttle run, 50-meter dash, standing long jump and handball throw) of the Ministry of Education, Culture, Sports, Science and Technology in Japan, and answered a questionnaire on life habits and subjective fatigue symptoms. The relationship between subjective fatigue symptoms and exercise habits and physical fitness level was examined by application of Quantification Method I. Multiple significant correlation (R = 0.295) was found, as well as partial correlations of the physical fitness level (r_xy = 0.10). However, significant partial correlations were also found in the life habits items other than exercise habit (r_xy = 0.07-0.12), and their item ranges (4.54-10.55) were higher than that of physical fitness level (5.87). In conclusion, although physical fitness level is one of the factors that affects subjective fatigue symptoms, many life habits other than exercise habits affect subjective fatigue as well. However, in these cases, the magnitude of their whole influence is not very large.

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Lifecorder EX (LC) is a useful accelerometer to assess physical activity, but its accuracy has not been assessed sufficiently: the effect of gender on LC accuracy remains unclear. This study was undertaken to examine gender effects on the LC accuracy to estimate the metabolic equivalent (MET) and LC accuracy during walking and running. The 45 healthy Japanese participants (23 male, 22 female) examined in this study were divided into two groups: a calibration group (16 male, 14 female) and a cross-validity group (7 male, 8 female). The participants performed 5 min of treadmill walking at 3.6, 4.8, and 6.0 km•h^-1, and treadmill running at 7.2 and 9.6 km•h^-1. The LC was placed on the waist. Simultaneous measurements obtained using the LC and an indirect calorimeter (IC) were recorded continuously during exercises. The gender effect was analyzed from data of the calibration group using mixed models. The LC accuracy was assessed with the cross-validation group using three-way repeated ANOVA models and root mean squared error (RMSE). In the calibration group, the results of mixed models revealed that the gender had no influence on the relationship between the IC measurements and the LC estimates (p > 0.577). In the cross-validation group, although no significant difference was found between the IC measurements and the LC estimates at any treadmill speed (p > 0.061), RMSE at running speeds (7.2 and 9.6 km•h^-1) rapidly increased more than those during walking. The results suggest that the LC can assess MET of men and women accurately, but the LC was unable to estimate MET during running.

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