Reliability and Acute Changes in the Load–Velocity Profile During Countermovement Jump Exercise Following Different Velocity‐Based Resistance Training Protocols in Recreational Runners

This study aimed (i) to explore the reliability of the load-velocity relationship variables (load-axis intercept [L₀], velocity-axis intercept [v₀], and the area under the load-velocity relationship line [A_line]) obtained during the countermovement jump exercise in successive sessions and (ii) to examine the feasibility of the load-velocity relationship variables to detect acute changes in the lower-body maximal mechanical capacities following different velocity-based training (VBT) protocols. Twenty-one recreational runners completed four randomized VBT protocols (three back squat sets with three minutes of rest) on separate occasions: (i) VBT with 60% of the one-repetition maximum (1RM) and 10% velocity loss (VBT_60-10); (ii) VBT with 60% 1RM and 30% velocity loss (VBT_60-30); (iii) VBT with 80% 1RM and 10% velocity loss (VBT_80-10); and (iv) VBT with 80% 1RM and 30% velocity loss (VBT_80-30). The load-velocity relationship was determined before and after each VBT protocol using the two-point method in the countermovement jump with a 0.5 kg load and another matching a mean velocity of 0.55 m·s^-1. All load-velocity relationship variables had an acceptable reliability (CV ≤ 5.61% and ICC ≥ 0.83, except for v₀ between VBT_60-30 and VBT_80-10). Both v₀ and A_line were reduced after VBT_60-30 and VBT_80-30 (p ≤ 0.044 and ES ≥ -0.47) but not after VBT_60-10 and VBT_80-10 (p ≥ 0.066 and ES ≤ -0.37). The post-pre differences were not significantly associated between VBT protocols for any load-velocity relationship variable (r ≤ 0.327 and p ≥ 0.148). Although the load-velocity relationship is reliable and sensitive to high-repetition VBT protocols, its use to detect acute changes in the lower-body maximal mechanical capacities is characterized by a high variability in individual responses.