Developmental characteristics in double- and single-leg jumping ability of elementary and junior high school students

Abstract

　This study aimed to investigate the developmental characteristics of the double- and single-leg countermovement jump (CMJ) and rebound jump (RJ) in elementary and junior high school students. A total of 823 students (401 boys and 422 girls) aged 7 to 15 years performed the CMJ, RJ, single-leg CMJ (SCMJ), and single-leg RJ (SRJ). To evaluate jumping ability, we measured the jumping height and RJ-index for the CMJ and SCMJ and for the RJ and SRJ, respectively. The main results obtained were as follows:
　1) In boys, both the CMJ and SCMJ jumping heights and the RJ and SRJ indices were shown to develop with age.
　2) In girls, the developmental characteristics of both CMJ and RJ ability differed between single-leg and doubleleg.
　3) In both sexes, the ground contact time in the SRJ increased significantly after age 9—10 years (p < 0.01).
　4) Regarding the CMJ jump height, a significant correlation was found between the CMJ and SCMJ in both sexes (p < 0.01). For the RJ-index, a significant correlation was found between the RJ and the SRJ in both sexes (p < 0.01).
　5) The number of boys and girls with a SRJ type may increase after junior high school, and the number of girls with a RJ type may decrease after junior high school.
　Our findings indicate that the developmental process of double- and single-leg jumping in elementary and junior high school students is similar in boys but different in girls. Comparison between double- and single-leg jumping ability showed that the CMJ had a high coefficient of determination, while the RJ had a lower value. Additionally, the number of boys and girls with a SRJ type may increase after junior high school. Therefore, especially when evaluating performance of the RJ, it is necessary to measure the performance of the double-leg and that of the single-leg.