The longitudinal data of the same subjects were mainly examined and such factors have been obtained as determining the development of motor reaction abilities of preschool children and of the amount of their development. The subjects range from tiny tots to six-year-olds. The total of 8,222 children of which 1,522 stayed the same during the two years, were examined for two successive years, and the stepwise-multiple regression analysis and principal factor analysis were mainly used and the following conclusions were obtained:
　I. The tendency of the development of the physique and motor abilities both by age and sex.
　1) The amount of the annual development of height increases gradually before they are two years old, and after they are three years old it gradually decreases. Weight increases fairly constantly: before they are four years old the increases is greater in the case of girls than in the case of boys, but after they are four years old, this difference disappears.
　2) Eight factors, both in the case of boys and girls, were obtained by examining the amount of the annual development of dexterity. Six groups of factors characterized by coordination, balance, agility, endurance of muscle, coordination-rhythm of fingers and flexibility common to both boys and girls. And the factor whose amount of the development decreases according to the age, that is, those of the ＼ Pattern in coordination and balance in the case of boys. The factor of the ／ Pattern is coordination of eyes and hands in the case of girls, and those of the ∨ Pattern are coordination-rhythm of fingers and agility in the case of both boys and girls, endurance power of the muscle in the case of boys and flexibility in the case of girls. Those of the ∧ Pattern are dynamic rhythm and flexibility in the case of boys, and in the case of girls coordination, endurance power of the muscle, balance, and muscle. And the pattern of the amount of the annual development differs from boys to girls.
　 II. The factors determining the amount of the annual development of motor abilities of children from three to six years old.
　1) The factors which greatly determine Energy System I (such basic motor abilities as running, jumping, throwing) are, in the case of both boys and girls, firstly Energy System II and Cybernetics System, and secondly such situations as natural feeding, short duration of TV watching and early start of walking.
　2) The factors closely related to the amount of the annual development of Energy System II (endurance of the muscle, muscle, and power) are Energy System I and physique (not of a corpulence in the case of both boys and girls). In the case of boys, such cases as using safe streets as the playgrounds and walking to and from nursery schools. In the case of girls, playing with their fathers for a long time on week days.
　3) The factors determining the amount of the annual development of Cybernetics System I (agility, balance, body coordination, dynamic rhythm) are Energy System I, Cybernetics II and to be young, to play a long time with their mothers, and a short duration of TV watching.
　4) The factors closely related with the amount of the annual development of Cybernetics II (coordination of eyes and hands, finger coordination) are Energy System I, Cybernetics I, and to be young.
　5) As for the factors determining the amount of the annual development of flexibility, clear tendencies were not found the thirty-six factors examined in this study.

DESCENTE SPORTS SCIENCE Vol.6/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE