## 4 Discussion
### Cmj  
Vertical jump height (imp-mom) and, more recently, RSImod are common CMJ reported metrics in the reviewed literature due to their association with various performance markers and their sensitivity to detect fatigue [7,23]. In this study, significant differences were observed in these metrics between trials, indicating an improvement in jump capacity with shortened contraction time, probably attributed to a learning and/or a warm-up effect, which enables the maximizing of jump height (imp-mom). Another potential source of error that could have influenced this increase in vertical jump performance is the inherent technical variability in human movement. In this case, executing the jump with a shorter contraction time may be associated with a shallower countermovement depth and/or higher eccentric velocities [44,45], which could result in greater concentric impulses due to a more effective utilization of the stretch-shortening cycle [46]. Both the impulse-momentum method and flight time estimation, along with the modified RSI, exhibited excellent intraclass correlation coefficients and coefficients of variation (Table 2). Comparing our findings with previous research [4], a similar pattern emerged. They also reported a percentage difference of 4.0 \(\pm\) 3.3% between trial 1 and trial 2 in NCAA D-1 volleyball players and excellent reliability (ICC \(>\) 0.93), which aligns with our investigation (Table 2). Despite the excellent reliability observed and the high familiarization of the participants with vertical performance tasks, these results suggest that it may be necessary to discard the first attempt in order to minimize sources of error from a possible learning effect or completion of warm-up. The majority of the kinetic, kinematic, and jump strategy variables of the present study demonstrated excellent reliability, except for certain eccentric phase variables such as peak force/BM, braking impulse, braking RFD, peak power, and peak power/BM (Table 2). [PERSON] et al. [39] also reported excellent intrasession reliability for no arm swing CMJ \"typical variables\", including performance metrics (ICC range = 0.873 to 0.967; CV range = 8.3 to 1.9%) concentric mean force (ICC = 0.965; CV = 2.8%) and power (ICC = 0.968: CV = 4.3%), concentric impulse (ICC = 0.987; CV = 2.2%), and concentric peak velocity (ICC = 0.958; CV = 1.9%). However, the reliability of kinetic, kinematic, and strategy variables during the eccentric phase of the jump generally exhibited lower values compared to the concentric phase (ICC range = 0.319 to 0.999; CV range = 23.5% to 0.4%). Considering the presented findings, it is important to note that variables withan ICC > 0.9 and a CV of \(<\)5% exhibit excellent reliability and can be confidently utilized. The decision to incorporate these variables into practice or research should be based on their internal logic and sensitivity to changes induced by intense exercise, as they have the potential to effectively detect fatigue [7]. Ultimately, coaches and sports scientists should carefully evaluate and select the most appropriate variables based on these considerations. No differences (\(p>0.05\)) were detected between the measured variables across the testing days when using the mean of three jumps. Intersession analysis showed that 52% (16/31) of the variables examined in the countermovement jump (CMJ) demonstrated excellent relative reliability. Furthermore, 71% (22/31) of the variables exhibited a coefficient of variation (CV) below 5%. Except for eccentric braking RFD, all variables displayed an ICC above 0.7 and a CV below 10%, indicating satisfactory reliability across all analyzed variables. Notably, the variables that exhibited the highest reliability were eccentric force/BM (ICC = 1.00; CV = 0.78%), concentric impulse (ICC = 0.98; CV = 1.66%), and concentric peak velocity (ICC = 0.93; CV = 1.61%). Similarly, [PERSON] et al. [9] showed that jump height, regardless of the calculation method, as well as RSImod, exhibited excellent intersession reliability criteria.