Development of rebound jumping ability in preschool children from age 2 to 6

This study investigated the development of rebound jumping ability in preschool children. The subjects included 100 boys (2 years: 8, 3 years: 19, 4 years: 33, 5 years: 30, and 6 years: 10) and 80 girls (2 years: 11, 3 years: 22, 4 years: 21, 5 years: 18, and 6 years: 8). The measurements used were jumping height in counter movement jumping (CMJ), index (jumping height/ground contact time) of consecutive rebound jumping (RJ), foot length, shank length, Achilles tendon length, relative Achilles tendon length (Achilles tendon length/shank length), relative foot length (foot length/shank length) and calf girth as morphological characteristics. The main results obtained were as a follows. 1) CMJ jumping height and RJ-index increased with age. Development of RJ-index depended on the increase in jumping height because ground contact time did not change even though jumping height increased with age. 2) CMJ and RJ ability development types were classified into 3 groups according to ±1 SD of the residual of regression line with age in months (good, equal, and poor groups). For RJ ability, the number of equal groups decreased significantly after 50 months in boy and girls. In addition, for boys, the number of individuals in the good group increased significantly after 50 months, whereas for girls, the number of individuals in the poor group increased significantly after 50 months. No such changes were found in CMJ ability. 3) RJ jumping height and ground contact time were compared among the 3 groups. The good group showed a significantly higher jumping height and shorter ground contact time than the other 2 groups. In addition, morphological characteristics showed no significant differences among the 3 groups. These results suggest that the development of RJ ability differs from that of CMJ ability, and that the development difference in RJ ability begins to become evident in infants over 50 months. In addition, it is suggested that this difference is influenced by factors other than morphological characteristics.