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.