Reliability and validity of free-weight countermovement jumps to characterize force-velocity-power profiles

The aim of this study was to determine test-retest reliability and concurrent validity of vertical force-velocity-power (FVP) profiles using Smith machine and free-weight countermovement jumps (CMJs). A repeated-measure cross-over design with randomized load order and counterbalanced trials was employed. Sixteen resistance-trained males (age: 26.4 ± 3.9 years, height: 179.6 ± 8.1 cm, body mass: 84.5 ± 10.8 kg) performed maximal loaded CMJs with 4–50 kg on six occasions, with three trials utilizing a Smith machine and three utilizing free-weights. Jump height was estimated with a linear-position transducer, and the Samozino computation method estimated theoretical maximal jump parameters. Reliability and concurrent validity were determined for jump height for each jump load and estimated theoretical maximal jump parameters using estimates of bias (mean difference, 95% limits of agreement) and agreement (intraclass correlation coefficients, ICCs). The jump height and maximum theoretical power demonstrated good-to-excellent reliability between sessions for both methods (ICC: 0.872–0.947) and concurrent validity between methods (ICC: 0.885–0.969). However, reliability for theoretical maximal force, velocity, and force-velocity gradient was not as high using either method (ICC = 0.320–0.615) and concurrent validity was poor (ICC: 0.122–0.340). In summary, using both jump methods, a linear-position transducer provides reliable jump height and theoretical maximal power values. However, our data do not support the reliability or validity of FV relationships using linear position transducers.