## 3 Results and Discussion  
### Simulations  
Table 1 presents strain in antero-posterior and vertical axes (8000 N centred) and resonance frequency of the first, third and final prototypes of above water 300 mm \(\times\) 250 mm, 500 mm \(\times\) 440 mm and underwater 600 mm \(\times\) 300 mm platforms, corroborating [PERSON]'s [20] suggestions for strain values between 100 and 500 \(\mu\epsilon\). The force plates design optimisation was a compromise among maximum rigidity, minimum mass and high frequency, which allows small deformations, uncoupling, good linearity and low hysteresis (c.f. [17]). The specific force plate application determined proper resonance frequencies and the maximal vertical load was supported. The waterproof force plate used by [PERSON] [20], with 500 mm \(\times\) 500 mm framed in galvanized steel, obtained a 35 Hz resonance frequency, which was considered sufficient for underwater applications due to over damping effects. However, in the current project, force plate versatility has been prioritized and values higher than \(\sim\)140 Hz were required (cf. [20]) as they can be both used independently of the starting block and out of the water. Commercial force platforms with a natural frequency \(\geq\)150 Hz have been well accepted for triple jump ground reaction forces assessment (e.g., [25]). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Project Evolution**} & \multicolumn{2}{c}{**Static and Dynamic**} & \multirow{2}{*}{**300 \(\times\) 250 mm**} & \multirow{2}{*}{**600 \(\times\) 300 mm**} & \multirow{2}{*}{**500 \(\times\) 440 mm**} \\  & & **Simulations** & & \\ \hline \multirow{3}{*}{First} & Antero-posterior (\(\mu\epsilon\)) & 323.0 & 470.0 & 297.0 \\  & Vertical (\(\mu\epsilon\)) & 464.0 & 489.0 & 473.0 \\  & Resonance frequency (Hz) & 235.7 & 153.0 & 140.0 \\ \hline \multirow{3}{*}{Third} & Antero-posterior (\(\mu\epsilon\)) & 287.0 & 357.0 & 349.0 \\  & Vertical (\(\mu\epsilon\)) & 545.0 & 521.0 & 511.0 \\  & Resonance frequency (Hz) & 323.7 & 197.0 & 177.0 \\ \hline \multirow{3}{*}{Final} & Antero-posterior (\(\mu\epsilon\)) & 290.0 & 375.0 & 376.0 \\  & Vertical (\(\mu\epsilon\)) & 545.0 & 541.0 & 279.0 \\ \cline{1-1}  & Resonance frequency (Hz) & 328.6 & 199.2 & 182.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Antero-posterior and vertical strain and their resonance frequency above 300 mm \(\times\) 250 mm, 600 mm \(\times\) 300 mm and 500 mm \(\times\) 440 mm underwater force plates of first, third and final prototypes. Table 2 shows results from one example of static simulation from each force plate considering all 24 strain gauge responses, which allow noticing maximal cross-talk less than 5% (cf. [20,21]). In fact, [PERSON]'s [19] findings have shown \(\sim\)3% of maximal interference among loads when 800 N had been applied. In addition, [PERSON] et al. [21] reported a cross-talk between orthogonal axes less than 5% for 40 N and 10 N of vertical and horizontal forces applied. The 300 mm \(\times\) 250 mm force plate laterally positioned on the starting block with fixed handgrip was simulated with a 2000 N load applied vertically on the handgrip, indicating an expectable relevant lateral force (strain gauges 17, 18, 23, 24; cf. Figure 4d). When 8000 N was centrally and vertically applied on a 600 mm \(\times\) 300 mm force plate, only strain gauges responsible for this measurement responded (i.e., 1 to 12, vertical force, antero-posterior and lateral moment; cf. Figure 4a,b).