When does the peak countermovement jump performance occur? Mapping peak-trial timing across six clustered repetitions.

Force-plate countermovement jump (CMJ) testing is widely used to assess neuromuscular status, yet monitoring interpretation often relies on best-trial values from abbreviated protocols, potentially biasing conclusions when the session maximum occurs beyond the sampled attempts. We mapped peak-trial timing across a six-trial clustered (3 + 3) CMJ protocol for seven outcome and strategy force-time metrics, and tested whether this peak-trial pattern was preserved between personal best (PB) and typical state (TS) monitoring sessions, both defined using modified reactive strength index (mRSI) as the primary selection variable. Retrospective dual-force-plate data (1000 Hz; August 2020-December 2025) were analysed from 314 athletes who performed two sets of three maximal no-arm-swing CMJs (5-10 s between repetitions; 60-90 s between sets). Peak-trial distributions deviated from uniform for all metrics (all Bonferroni-adjusted p ≤ 3.4 × 10-3; Cramér's V = 0.12-0.26). On PB days, the most frequent peak occurred on repetition 4 for output metrics (25.8-30.3%) and propulsive power (29.3%), on repetition 6 for braking force/power (31.2-34.1%), and on repetition 1 for stiffness (27.4%) and propulsive force (31.8%). Critically, peak-repetition distributions were nearly identical between PB and TS days for every metric (all p ≥ 0.386; Cramér's V ≤ 0.091).