Differences in Joint Mechanics Between Adolescent and Adult Males Performing Countermovement and Drop Jump Tasks

Abstract

PURPOSE: To investigate the differences in joint mechanics between adolescent and adult males performing countermovement and drop jump tasks. METHODS: Eleven adolescent basketball players (age: 16.5 ± 0.7 years; height: 1.78 ± 0.07 m; mass: 68.9 ± 8.8 kg) and eleven resistance-trained adults (age: 22.3 ± 1.9 years; height: 1.80 ± 0.10 m; mass: 84.3 ± 9.3 kg) performed two trials of a countermovement jump (CMJ) and a drop jump from a height of 0.40 m (DJ). Force plates (1000 Hz) and an 8-camera 3-D motion analysis system (200 Hz) were used to determine the following kinetic variables for the hip, knee, and ankle joints during the propulsive phase of each jump: normalized work performed by the moment (JWNORM), normalized power output of the moment (JPONORM), and normalized joint stiffness (JSNORM). RESULTS: The adults produced significantly greater JWNORM across the two jumps (mean difference [MD]: 0.32 J/kg, p=0.014). JWNORM at the knee was greater than that at the hip (MD: 2.09 J/kg, p<0.001) and the ankle (MD: 2.61 J/kg, p<0.001), while JWNORM was greater at the hip compared to the ankle (MD: 0.52 J/kg, p=0.001). The adults performed greater JWNORM at the hip compared to the adolescents (MD: 0.75 J/kg, p=0.005). JPONORM at the knee was greater than that at the hip (MD: 4.49 W/kg, p<0.001) and ankle (MD: 4.32 W/kg, p<0.001) across the two jumps while JPONORM was significantly greater in DJ compared to CMJ (MD: 0.49 W/kg, p=0.10). The adolescents produced significantly greater JPONORM at the ankle compared to the adults (MD: 1.35 W/k, p=0.002). The adolescents produced significantly greater JSNORM compared to the adults (MD: 0.021 Nm/kg/deg, p<0.001). Both groups produced significantly greater JSNORM in DJ compared to CMJ (MD: 0.015 Nm/kg/deg, p=0.001) with significant increases in JSNORM at the knee joint from CMJ to DJ (MD: 0.02 Nm/kg/deg, p<0.001). The increase in JSNORM at the hip (MD: 0.025 Nm/kg/deg, p=0.033) and knee (MD: 0.023 Nm/kg/deg, p=0.046) between CMJ and DJ was significantly greater in adolescents compared to adults. CONCLUSION: Adolescent males produce different joint mechanics compared to adults during jumping tasks and rely on a strategy of increasing joint stiffness at the hip and knee joints when performing DJ. These differences may have implications for musculoskeletal injuries in adolescent males.