## 4 Discussion  
The aim of this study was to assess the acute effects of combined isometric and pylometric unilateral CAs on subsequent CMJ and 50 m sprint performance (with split measures at 0-20 and 0-40 m) in sprinters. Considering the current state of knowledge, it seemed fully justified to evaluate possible changes in motor pattern changes and the role of the speed of CA in determining the significance of exercise selection to elicit PAPE. The main findings of this study are that the applied CA led to an acute improvement in the following 20 m and 40 m sprint performance, with no significant impact on the 50 m sprint time. Contact time and flight time during the 50 m sprint did not change due to the PAPE intervention. Moreover, a significant increase in CMJ height and RSI due to the CA was observed. Considering the positive effects of various resistance exercise activation protocols on sprint performance, e.g., isometric, concentric, eccentric, and pylometric [10; 11; 23], the authors of this study aimed to evaluate the combined effects of these resistance exercise modalities on sprint performance. To the best of our knowledge, only the study by [PERSON] et al. [24] has, so far, investigated the acute effects of combined isometric and pylometric CA (comparing CAs performed in a bilateral and a unilateral manner) on CMJ performance. The authors reported a significant increase in CMJ height (from 32.5 \(\pm\) 4.9 cm to 34.7 \(\pm\) 4.6 cm; +2.2 cm, -7.7 \(\pm\) 8.5%) and RSImod (0.33 \(\pm\) 0.06 to 0.36 \(\pm\) 0.06; +0.3 m/s; 12 \(\pm\) 15%) 6 min after two sets of 6 s of maximal bilateral half-back squats, immediately followed by 10 repetitions of drop jumps. Conversely, the unilateral protocol, consisting of 3 s of maximal effort per leg during unilateral single-leg squats, followed by five drop jumps per leg, resulted in a non-significant improvement in CMJ height (from 33.2 \(\pm\) 5.5 cm to 34.2 \(\pm\) 5.5 cm; +1 cm, 3.1 \(\pm\) 6%) and RSImod (0.34 \(\pm\) 0.07 to 0.36 \(\pm\) 0.08 m/s; +0.02 m/s, 4 \(\pm\) 9%). The CMJ height improvements observed in the present study were of similar magnitude to those reported following unilateral CA in [PERSON] et al. [24]'s study. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Pre-CA (95\%Cl)** & **Post-CA (95\%Cl)** & **d (95\%Cl)** & **\%** \\ \hline \multicolumn{4}{c}{20 m sprint time [s]} \\ \hline
2.975 \(\pm\) 0.118 & 2.952 \(\pm\) 0.117 & \(-\)0.2 & \(-\)0.8 \(\pm\) 0.9 \\ (3.047 to 2.904) & (3.022 to 2.881) & (\(-\)0.966 to 0.575) & \\ \hline \multicolumn{4}{c}{40 m sprint time [s]} \\ \hline
5.143 \(\pm\) 0.215 & 5.12 \(\pm\) 0.21 & \(-\)0.11 & \(-\)0.5 \(\pm\) 0.6 \\ (5.273 to 5.013) & (5.245 to 4.992) & (\(-\)0878 to 0.661) & \\ \hline \multicolumn{4}{c}{50 m sprint time [s]} \\ \hline
6.242 \(\pm\) 0.275 & 6.23 \(\pm\) 0.27 & \(-\)0.04 & \(-\)0.2 \(\pm\) 0.5 \\ (6.408 to 6.076) & (6.393 to 6.067) & (\(-\)0.813 to 0.725) & \\ \hline \multicolumn{4}{c}{Contact time [ms]} \\ \hline
0.112 \(\pm\) 0.005 & 0.112 \(\pm\) 0.004 & 0 & \(-\)0.1 \(\pm\) 2.8 \\ (0.115 to 0.109) & (0.114 to 0.109) & (\(-\)0.769 to 0.769) & \\ \hline \multicolumn{4}{c}{Flight time [ms]} \\ \hline
0.120 \(\pm\) 0.005 & 0.120 \(\pm\) 0.006 & 0 & \(0.6\pm 1.9\) \\ (0.123 to 0.116) & (0.124 to 0.117) & (\(-\)0.769 to 0.769) & \\ \hline \end{tabular}
\end{table} 
Table 1: _S_print performance before and after the conditioning activity. Specifically, the relative improvements in CMJ (\(\sim\)2.6%), RSImod (\(\sim\)4.1%), and 20 m sprint time (\(-\)0.8%) were statistically significant. An increase of 1.4 cm in CMJ height or a 23 ms reduction in the 20 m sprint time can yield meaningful competitive advantages for elite athletes, with these findings highlighting the relevance of even small enhancements in performance following combined isometric and pyometric CA. Notably, [PERSON] et al. [24] included female semi-professional volleyball players as participants.