Abstract
The developmental changes in factorial structure of motor ability were investigated with longitudinal data of junior high school girls in this paper. First of all, the principal component analysis was applied to the correlation matrix of each grade, whose variables were 13 motor ability items and 4 anthropometric variables, and the first principal components were extracted and investigated. These components could be interpreted as fundamental motor ability components, because of significant loading with all variables, and their degrees of contribution to total variance were decreasing as the age grew. In other words, the individual differences in the fundamental motor ability may be decreasing as the age grows. Then, the principal factor analysis was applied to these correlation matrices with communalies estimated by the results of principal component analysis under the hypothesis of numbers of factors estimated by the same results, and normal varimax rotation was applied to the extracted factor matrices. Five factors were extracted in each grade, but the interpreted factors were not always the same in each grade, but two of them were identical; factor of power and coordination, and growth of longitudinal element of physique. The contribution of the format factor to total variance is increasing as the age grows but the later one decreasing. Investigation on communality changes showed that the specificity of variables increasing in physique, static dynamometric strength and flexibility, but decreasing in power and coordination variables. In other words, the relationship of power and coordination variables with other areas of motor ability was increasing as the age grew.
