Abstract
To date, the author has discussed the physical ability of children and youths in a series of studies under separate titles. The author has had the opportunity to continue his research on twins in the Osaka municipal primary and junior high schools in 1954 and on children in a fishing village on the Island of Oki and in a rural village in Kagawa Prefecture in 1955. The investigated physical traits were stature, the height of the ventral iliac spine, girth of the upper thigh, back muscle strength, sergent jump, tapping (manual repetition of motor speed), the match board test (manual dexterity) and picking up balls (finger dexterity).
An analysis of the resulting data may be briefly summarized as follows:
1. No differences in physical ability are found between the two groups of monozygotic and dizygotic twins.
2. The twin groups are never inferior in stature to ordinary urben children living under the same urban circumstances.
3. Comparing children dwelling urban districts with those in rural and fishing villages, some differences are found in physical ability and even in the types and phases of their growth and development, and it appears that these differences have some relation to the conditions under which they are living.
4. The eight investigated physical traits are classified into five groups according to types of growth and development.
5. Some differences are found in growth and development patterns and it appears that physical ability requires greater muscle power which developes earlier than ability which requires less muscle power.
