Changes in the eccentric phase contribute to improved stretch-shorten cycle performance after training

PURPOSE: To determine whether ballistic power training and strength training result in specific changes in stretch-shorten cycle (SSC) function during the eccentric (ECC) phase and, if so, whether these changes are influenced by the individual's strength level. METHODS: Thirty-two male subjects were divided into four groups: stronger power training group (SP, n = 8, squat one-repetition maximum-to-body mass ratio (1RM/BM) = 1.97 ± 0.08), weaker power training group (WP, n = 8, 1RM/BM = 1.32 ± 0.14), weaker strength training group (WS, n = 8, 1RM/BM = 1.28 ± 0.17), or control group (C, n = 8, 1RM/BM = 1.37 ± 0.13). Training involved three sessions per week for 10 wk. The SP and WP groups performed maximal-effort jump squats with 0%-30% 1RM, and the WS group performed back squats at 75%-90% 1RM. Maximal strength, jump performance, musculotendinous stiffness, and neural activation were assessed before training and after 5 and 10 wk of training. RESULTS: Both power and strength training elicited significant changes in a multitude of ECC variables that were significantly associated with improvements in concentric (CON) performance. Enhancements in CON performance were theorized to be driven by the development of a strategy to better use the ECC phase during jumping (i.e., greater unloading allowed for increased negative acceleration and thus velocity during the countermovement and improved musculotendinous stiffness resulted in an enhanced ability to translate the momentum developed during the ECC phase into force). Although a significant improvement in maximal strength resulted in changes to SSC function during the ECC phase, the initial strength level did not significantly affect the ECC variables before training or the magnitude of adaptations in individuals exposed to ballistic power training. CONCLUSIONS: Training-induced alterations in SSC function during the ECC phase contributes to improvements in jump performance after both ballistic power training and heavy strength training.