Exploratory Associations of Heart Rate and Running Velocity at Fixed Blood Lactate Concentrations with Sprint and Jump Performance in Male U19 Soccer Players

Background: Relationships between heart rate and running velocity at fixed blood lactate concentrations with short-duration performance remain uncertain in U19 soccer players. This exploratory cross-sectional study examined their associations with 10 m sprint time and countermovement jump (CMJ) height. Methods: Sixteen male players from a U19 development squad completed CMJ and 10 m sprint assessments followed by an incremental field-running test. The best result from two CMJ and two sprint trials was analyzed. Pearson correlations were reported with 95% confidence intervals, and the Benjamini–Hochberg procedure controlled the false discovery rate (FDR) across 24 tests. Results: Nominal positive correlations were observed between 10-m sprint time and heart rate at fixed blood lactate concentrations of 2.0–3.5 mmol·L−1 (r = 0.503–0.579; raw p = 0.019–0.047), indicating that higher heart rate was associated with longer sprint time. None remained statistically significant after FDR correction (q ≥ 0.207). No CMJ or running-velocity association survived FDR correction. Conclusions: The data did not provide multiplicity-corrected evidence of associations between fixed-concentration test responses and sprint or jump performance. The estimates are exploratory and require confirmation in larger, prospectively powered samples.