The present study was conducted to investigate longitudinal changes in the strength and power of the lower limb using the rebound jump (RJ) test. Forty-one male jumpers performed the RJ test, which was conducted at least twice in a 12-month period, and the data from the 2 tests were analyzed. The performance (RJ-index, contact time and jump height) and joint kinetics (joint power and joint work) in the RJ were then calculated. In order to investigate the changes in performance, the IAAF Athletics Scoring Tables were used to calculate jump event performance (IAAF score). When the RJ-index increased, the jump height was significantly increased and the contact time was significantly shortened. The power and work of the ankle and hip joints were significantly increased. Therefore, the contact time was shortened, and the jump height was increased at the same time by increasing the power and work of the ankle and hip joints. The subjects were divided into 3 groups based on the average value ± 0.5 SD of the contact time and jump height in the first RJ test. This revealed that the contact time was shortened when the initial value was long, but was difficult to change when the initial value was short. Furthermore, the jump height was not dependent on the initial value and increased with changes in the mechanical values for the ankle and hip joints.<br> These findings suggest that the characteristics of changes in joint mechanics in addition to jump height and contact time are clues to the training task, and that it is necessary to consider the initial value of the contact time.