ABSTRACT
Common methods to estimate vertical jump height (VJH) are based on the measurements of flight time (FT) or vertical reaction force. This study aimed to assess the measurement errors when estimating the VJH with flight time using photocell devices in comparison with the gold standard jump height measured by a force plate (FP). The second purpose was to determine the intrinsic reliability of the Optojump photoelectric cells in estimating VJH. For this aim, 20 subjects (age: 22.50±1.24 years) performed maximal vertical jumps in three modalities in randomized order: the squat jump (SJ), counter-movement jump (CMJ), and CMJ with arm swing (CMJarm). Each trial was simultaneously recorded by the FP and Optojump devices. High intra-class correlation coefficients (ICCs) for validity (0.98-0.99) and low limits of agreement (less than 1.4 cm) were found; even a systematic difference in jump height was consistently observed between FT and double integration of force methods (-31% to -27%; p<0.001) and a large effect size (Cohen's d>1.2). Intra-session reliability of Optojump was excellent, with ICCs ranging from 0.98 to 0.99, low coefficients of variation (3.98%), and low standard errors of measurement (0.8 cm). It was concluded that there was a high correlation between the two methods to estimate the vertical jump height, but the FT method cannot replace the gold standard, due to the large systematic bias. According to our results, the equations of each of the three jump modalities were presented in order to obtain a better estimation of the jump height.
ABSTRACT
This study compared the effect of counter-movement-jump (CMJ)-based recovery on repeated-sprint-ability (RSA). Eighteen male footballers (16 ± 0 years, 65 ± 10 kg, 1.74 ± 0.10 m) performed three RSA-tests. RSA-1/-3 were performed according to standard procedures, while three CMJs (over 10â³) - as a potential fatigue-determinant and/or running mechanics interference--were administered during RSA-2 recoveries. RSA performance, exercise effort (fatigue index [FI], rating of perceived exertion [RPE], blood lactate concentration [BLa]), simple kinematics (steps number), vertical-jump characteristics (stretch-shortening-cycle-efficiency [SSCE] assessed before/after RSA) were investigated. ANOVA showed no differences between RSA-1,-3. During RSA-2, performance was lower than RSA-1/-3, while steps number did not change. During RSA-2, FI, BLa, RPE were higher than RSA-1/-3 (FI +21.10/+20.43%, P<0.05; BLa +16.25/+13.34%, P<0.05; RPE +12.50/+9.57%, P<0.05). During RSA-2, SSCE, as the CMJ/squat-jump-height-ratio, was not significantly different from RSA-1/-3. Passive recovery RSA allows better performance. Yet, RSA CMJ-based recovery is effective in increasing training load (FI, BLa, RPE) without perturbing running mechanics (simple kinematics, SSCE).
