Effects of a short-term detraining period on slow and fast stretch-shortening cycle performance in elite female volleyball players

The aim of this study was to examine the effects of short-term detraining on slow and fast stretch-shortening cycle (SSC) performance in elite female volleyball players using countermovement jump (CMJ) and countermovement rebound jump (CMJ-RE) assessments. Eleven professional female volleyball players competing in the Spanish First Division completed three testing sessions: two separated by 24 h to assess test–retest reliability, and a third performed after a 10-day mid-season winter break to evaluate pre–post changes. In each session, players performed three CMJ and three CMJ-RE trials on portable dual force plates sampling at 1000 Hz. Reliability was assessed using intraclass correlation coefficients, coefficient of variation, standard error of measurement, and smallest detectable difference. Pre–post changes were examined using paired t-tests with Hedges’ g effect sizes. No statistically significant changes were observed in any CMJ metric (p > 0.05). However, in CMJ-RE, concentric impulse showed a statistically significant reduction of trivial magnitude (p = 0.046; ES = −0.10). Individual response analysis showed decreases exceeding the SDD in concentric impulse in two players and in mRSI in one player, whereas most individual changes remained within the SDD. Overall, slow-SSC performance, captured through CMJ force–time metrics, was largely maintained, whereas fast-SSC performance, assessed using the CMJ-RE, revealed a statistically significant decrease only in concentric impulse. These findings suggest that CMJ-RE may provide complementary information alongside traditional CMJ assessment when examining SSC performance after short in-season breaks.