Fig. 1

The phenotypic regression model Note: Dashed lines between the early motor development traits and the exercise behaviors are single headed arrows denoting the regression relations. Continuous double headed arrows denote the correlations between the two motor development traits and between the residuals of exercise behavior at the various ages. MD-FS, the factor score of motor development before age 2; GM5, gross motor development at age 5; MET7, MET10, MET12, and MET14 represent the voluntary exercise behavior at each age (7, 10, 12, and 14 years); R7, R10, R12, and R14 represent the residuals of the predicted exercise behaviors at each age