Age-related differences in kinetics during double- and single-leg jumps in boys

BACKGROUND: Plyometric training, such as single-leg jumps, may be one of the most effective ways to improve a child's jumping and sprint-ing ability. However, few studies on age-related changes in single-legged jumping ability seem to exist. Therefore, the aim of this study was to examine age-related changes in double-and single-leg jump performance.METHODS: A total of 143 untrained boys aged 7-15 years performed double-leg counter-movement jump (CMJ) and rebound jump (RJ) and single-leg CMJ (SCMJ) and RJ (SRJ). Jump height (JH), peak vertical ground reaction force (PvGRF), and relative vertical ground reaction force (RvGRF) during CMJ and SCMJ, and RJ-Index, JH, ground contact time (CT), PvGRF, and RvGRF during RJ and SRJ were recorded, and one-way analysis of variance was used to examine differences between age group.RESULTS: JH, PvGRF, and RvGRF of CMJ and SCMJ increased with age with a similar trend (P<0.001). RJ-Index, JH, and PvGRF of RJ and SRJ also increased with age (P<0.001). CT of RJ did not change with age, but SRJ became longer with age (P<0.001). The RvGRF of RJ increased with age (P<0.001), but the RvGRF of SRJ did not change. CONCLUSIONS: These results suggest that age-related changes in CMJ among boys aged 7-15 years have similar trends for double-and single-leg jumps. However, age-related changes of RJ differed between double-and single-leg jumps, suggesting that differences in adaptation of relative force exertion may occur.