Reliability and Acute Changes in the Load-Velocity Profile During Countermovement Jump Exercise Following Different...

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.