Free-fall normalised peak braking velocity for countermovement jump monitoring.

BACKGROUND: Peak braking velocity (PBV) during the countermovement jump (CMJ) is used to describe descent strategy, but its interpretation is affected by countermovement depth. This study introduced free-fall normalised peak braking velocity (PBVFF), a dimensionless index expressing PBV relative to the displacement-specific theoretical free-fall velocity limit, and evaluated its reliability, performance associations and ranking consequences. METHODS: Seventy injury-free male academy footballers (18.7 ± 1.6 years) performed three maximal hands-on-hips CMJs on dual force plates. Using retrospective observational routine monitoring data, one representative testing day per athlete was analysed. Two PBVFF variants were examined: PBVFF normalised to countermovement depth (PBVFFCMD) and PBVFF normalised to displacement at PBV (PBVFFPBV_d). Reliability was assessed using coefficient of variation and two-way mixed-effects intraclass correlation coefficients. Associations with modified reactive strength index (mRSI) and jump height (JH) were assessed using Pearson correlations, Benjamini-Hochberg false discovery rate correction and partial correlations controlling for JH. Ranking effects were examined using Spearman rank correlations, Kendall's coefficient of concordance and absolute rank shifts. RESULTS: PBVFFCMD showed reliability comparable to raw PBV, with a pooled coefficient of variation of 5.81% versus 6.75% and three-trial intraclass correlation coefficients of 0.865 versus 0.888, respectively. PBVFFCMD was more strongly associated with mRSI than raw PBV (r = 0.573 versus r = 0.231). After controlling for JH, the association between raw PBV and mRSI reversed direction (partial r = - 0.266), whereas the association for PBVFFCMD remained positive (partial r = 0.531). PBVFFPBV_d showed similar but weaker associations with mRSI (r = 0.430; partial r = 0.438). Switching from raw PBV to PBVFFCMD reclassified 46% of athletes by at least 10 ranking positions. CONCLUSIONS: PBVFF provides a depth-contextualised interpretation of CMJ descent strategy without compromising within-session reliability. PBVFFCMD appears particularly practical because it can be derived from commonly exported variables and may improve athlete monitoring by reducing misinterpretation driven by countermovement-depth and anthropometric differences. It should complement, rather than replace, established force-time and performance metrics. TRIAL REGISTRATION: Not applicable.