Effect of exhausting stretch-shortening cycle exercise on the time course of mechanical behaviour in the drop jump: possible role of muscle damage

The purpose of the present study was to investigate the effect of stretch-s hortening-cycle-induced muscle damage on the time course of mechanical beha viour in the drop jump. Ten healthy male subjects performed submaximal stre tch-shortening cycle (SSC) exercise on a special sledge apparatus. Exhausti on occurred on average within 3 min. A drop jump (DJ) test from a 50-cm hei ght was performed before and immediately after the sledge exercise as well as 3 h, 2 days and 4 days later. The fatigue exercise showed relatively hig h blood lactate concentration [12.5 (SD 2.6) mmol . l(-1)] and an increase of serum creatine kinase (CK) activity delayed by 2 days [540 (SD 407)U . l (-1)]. The initial decline in the jump performance (before - immediately af ter) was related negatively to the early recovery in performance (immediate ly after - 2 h) (P < 0.05). The early recovery of the knee joint moment at the end of stretch showed a negative correlation to the delayed decrease in DJ performance (2 h - 2 days) (P < 0.01). Thus, the DJ performance showed an initial decline followed by an early recovery and a secondary decline. B oth the initial decline and early recovery in the knee joint moment at the end of stretch were related to the corresponding initial (after - 2 h) (P < 0.05) and secondary increases (2 h - 2 days) (P < 0.01) in CK. It is sugge sted that the early recovery as well as the initial decline in the knee joi nt function could depend on the degree of muscle damage. Delayed decrease i n initial stiffness (2 h - 2 days) was negatively related to the correspond ing changes in the knee joint angle at touch down in DJ (P < 0.001). These interactions would imply that the decrease in the stiffness regulation and the modulation of the prelanding motor control might be attributable to sec ondary muscle damage during 2 days after the SSC exercise. Therefore, it ma y be suggested that the changes in the DJ performance after the exhausting SSC exercise accompany the progress of muscle damage observed by the corres ponding increase in serum CK concentration and the corresponding deteriorat ion of stiffness regulation and motor control in DJ.