This study examined the change in countermovement jump (CMJ) performance across a microcycle of training in professional soccer players during the in-season period. Nine elite youth soccer players performed a CMJ test pre and post four consecutive soccer training sessions of an in-season weekly microcycle. Training load was quantified using global positioning systems (GPS), heart rate (HR) and rating of perceived exertion (RPE). Absolute change (pre to post training) in CMJ height across each training session was analysed using one-way repeated measures analysis of variance (ANOVA). Magnitude of effects was reported with the effect size (ES) statistic. Correlation analyses assessed the relationships between training load measures and the absolute change in CMJ height. Training load remained similar on all training days apart from a significant decrease in training load (all variables except high speed distance) on the last training session (P 0.05). This study revealed no significant change in CMJ performance across the in-season microcycle. This suggests that soccer players are able to maintain CMJ performance across an in-season training microcycle
