Assessment of the force‐velocity relationship during vertical jumps: influence of the starting position, analysis procedures and number of loads

This study aimed to compare the reliability and magnitude of the force‐velocity (F‐V) relationship parameters between the squat jumps performed from the 90° (SJ90) and self‐preferred knee angle (SJpref). A secondary aim was to explore the effect of the analysis procedure (force platform [FP] and Samozino's [SAM] method) and the number of loads tested (three‐ and two‐point methods) on the F‐V relationships. Twelve men were tested in two sessions during the SJ90 and SJpref. Two identical blocks of jumps were performed in each session against three external loads. The F‐V relationship parameters (maximum force, maximum velocity, F‐V slope and maximum power) were determined at each block through the FP and SAM procedures using the data collected under three (three‐point method) or only the two most distant loads (two‐point method). The average coefficient of variation (CV) of the four F‐V parameters revealed a higher reliability for the SJ90 compared to the SJpref (5.86% vs. 7.55%; CVratio = 1.29) with more pronounced differences using the FP (CVratio = 1.43) than the SAM procedure (CVratio = 1.14), and higher reliability for the SAM compared to the FP (6.14% vs. 7.27%; CVratio = 1.18). The SJpref and SAM procedures provided comparable or higher magnitude of the F‐V relationship parameters than the SJ90 and FP, respectively. The three‐ and two‐point methods revealed a comparable reliability and trivial differences in the magnitude of the F‐V relationship parameters. The routine testing procedure of the F‐V relationship could be simplified using the SJpref, the SAM procedure and the two‐point method.