The purpose of this study was to estimate genetic and environmental effects on physical fi tness and motor performance. Subjects for this study were 90 pairs of monozygotic twins (MZ) and 68 pairs of dizygotic twins (DZ), a total of 316 subjects between 10 to 15 years old. Six items were used for physical fi tness and motor performance data: grip strength, sit-ups, sit and reach, side step, 50 meter run and standing broad jump. The correlation analysis and the model-fi tting analysis have been done based on the type of each set of twins. For the model-fi tting analysis, models that give effects of additive genes (A), nonadditive genes (D), common environment (C), and specifi c environment (E) on phenotypes of physical fi tness and motor performance have been applied. The following could be presumed as a result of a correlation analysis: the results showed for the grip strength and the side step that rMZ was greater than rDZ, and rDZ was greater than half of rMZ, therefore, it could be stated that there were effects from additive genetic and common environmental factors. The results from the sit-ups and the 50 meter run showed that rMZ and rDZ were almost equal to each other, therefore, it could be stated that there was no genetic effect. The correlation ratio of rMZ and rDZ was 2:1 for the category of sit and reach, therefore, the resemblance among MZ was from the genetic effect only. As for the standing broad jump, rDZ was smaller than half of rMZ, therefore, there were effects of additive genetic and nonadditive genetic factors. From the results of the model-fi tting analysis, the following could be stated: the best fi tting models for grip strength, sit and reach, and the standing broad jump, where additive genetic and specifi c environmental factors affect phenotypes, were the AE model, and the coeffi cient of determination of additive genetic factor, at between 52.2% and 76.9%, was relatively high. For the side step, where additive genetic, common environmental and specifi c environmental factors have effects on phenotypes, the best fi tting model was the ACE model, and each coeffi cient of determination was 32.4%, 39.4% and 28.1%. No genetic effect was observed for sit-ups and the 50 meter run. The coeffi cient of determination for sit-ups was 51.1% in a common environment and was 48.9% in a specifi c environment. S-CE was the best fi tting model for the 50 meter run, where the effect varies depending on sex, and the coeffi cient of determination for boys were 75.5% for common environment and 24.4% for specifi c environment, whereas those for girls were 53.0% and 46.9% respectively.

No single factor has yet emerged to date in the literature on personality, and it is unlikely that one will ever be found given the diversity of traits subsumed under the category of personality. We hypothesized that experiences of crisis, exploration, and commitment in athletic and daily life events affect personality. This study examined the relationship between experiences of athletic and daily life and personality in Japanese senior high school students by using multiple regression analysis. We had senior high school students (189 males and 118 females) complete a questionnaire assessing their experiences of crisis, exploration, and commitment on four issues (Teammates, Authority Figures, Competition Results, Contest Continuation) in the athletic domain, and on six issues (Study, Future Courses, Values, Family, Opposite Sex Friends, Same Sex Friends) in the daily life domain. Our results reveal that, there are significant models for factors of Extraversion and Neuroticism in males with less than 10 years of experience; for males with over 10 years of experience, there were significant models for factors of Neuroticism. Moreover, for males with less than 10 years of experience, there were significant relationships between personality with regards to exploration in the athletic domain and daily life domain; for males with over 10 years of experience, there were significant relationships between personality with regards to commitment in the athletic domain, crisis, and commitment in the daily life domain. For females with less than 10 years of experience, there was no significant difference; for females with over 10 years of experience, there were significant relationships between personality with regards to crisis in the athletic domain. Thus, there was a more significant relationship between various experiences and personality in males than females. Similar to previous research examining personality, this study highlights the importance of including experiences of crisis, exploration, and commitment when taking part in sports activity.

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