## 2 Materials and Methods
### Study Participants  
A priori, the sample size was calculated within the statistical software G*Power, (Dusseldorf, Germany) [version 3.1.9.2]. The calculation was based on the following statistical variables: 'ANOVA, repeated measures, and within-between interaction' (three groups of study participants, two experimental conditions, two measurements for each condition) including the statistical power of 0.9, a significance level of 0.05, and a d Cohen's effect size of 0.25. Based on the calculations, a minimum sample size of 54 individuals was obtained. Initially, sixty-four karate athletes agreed to participate in this study; however, three of them withdrew from the experiment. A total of 61 (female = 28; male = 33; mean age = 17.48 \(\pm\) 3.26 [years]; mean body height = 1.73 \(\pm\) 0.08 [m]; mean body mass = 63.79 \(\pm\) 10.00 [kg]) elite WKF komite athletes from the Polish national team participated in this study. Several of them were medalists of the European Championships, World Championships, or World Senior's League--Karate 1--Series A. Moreover, all study participants were experienced in strength and conditioning training (Table 1). The inclusion criteria were as follows: (1) kumite athlete (WKF formula) of the Polish national team who has valid permission from a sports physician to participate in competition (karate WKF), (2) males and females in the following WKF age categories: U16 (14-15 years old), U18 (16-17 years old), and Seniors (18-34 years old), (3) at least 5 kyr (blue belt), (4) at least 3 years of kumite training experience at an elite level, and (5) at least 2 kumite training sessions per week. The exclusion criteria were as follows: (1) an occurrence of an injury in the last six months that resulted in exclusion from training for a period longer than 14 days, (2) withdrawal from this study, (3) WKF kumite athletes with disabilities, and (4) pregnancy (with regard to female athletes). Table 1 provides a detailed description of the study participants. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & **All Study Participants** & **U16** & **U18** & **Seniors** & **Between-Group** \\  & **(nP = 61; nF = 28; nM = 33)** & **(nP = 12)** & **nM = 12)** & **nM = 12)** & **nM = 9)** & **0.3** \\  & **(Mean \(\pm\) SD)** & **(Mean \(\pm\) SD)** & **(Mean \(\pm\) SD)** & **(Mean \(\pm\) SD)** & **(Mean \(\pm\) SD)** & **(\(p\)-Value)** \\ \hline Age [years] & 17.48 \(\pm\) 3.26 & 14.5 \(\pm\) 0.51 & 16.63 \(\pm\) 0.5 & 20.91 \(\pm\) 2.91 & 0.001 * (ES = 0.91) \\ \hline Body mass [kg] & 63.79 \(\pm\) 10.00 & 60.43 \(\pm\) 9.16 & 63.72 \(\pm\) 9.44 & 66.91 \(\pm\) 10.61 & 0.07 \\ \hline Body height [m] & 1.72 \(\pm\) 0.08 & 1.7 \(\pm\) 0.08 & 1.73 \(\pm\) 0.06 & 1.74 \(\pm\) 0.09 & 0.3 \\ \hline BMI [kg/m\({}^{2}\)] & 21.38 \(\pm\) 2.61 & 20.83 \(\pm\) 2.87 & 21.3 \(\pm\) 2.42 & 21.95 \(\pm\) 2.41 & 0.15 \\ \hline Muscle mass [kg] & 30.68 \(\pm\) 6.11 & 29.32 \(\pm\) 5.41 & 30.52 \(\pm\) 5.87 & 32.05 \(\pm\) 6.84 & 0.37 \\ \hline Fat mass [kg] & 8.89 \(\pm\) 4.31 & 7.98 \(\pm\) 4.71 & 9.34 \(\pm\) 4.42 & 9.33 \(\pm\) 3.87 & 0.56 \\ \hline Kumite training experience [years] & 10.31 \(\pm\) 3.97 & 7.53 \(\pm\) 1.93 & 9.82 \(\pm\) 2.81 & 13.27 \(\pm\) 4.25 & 0.001 * \\ \hline Number of kumite training sessions per week [\(n\)] & 4.43 \(\pm\) 1.26 & 3.93 \(\pm\) 1.24 & 4.71 \(\pm\) 1.28 & 4.64 \(\pm\) 1.18 & 0.1 \\ \hline Standard kumite training (hours) & 1.52 \(\pm\) 0.24 & 1.52 \(\pm\) 0.2 & 1.53 \(\pm\) 0.26 & 1.5 \(\pm\) 0.26 & 0.93 \\ \hline SC training experience (years) & 3.48 \(\pm\) 2.61 & 2.58 \(\pm\) 1.61 & 3.0 \(\pm\) 2.0 & 4.7 \(\pm\) 3.33 & 0.08 \\ \hline \hline \end{tabular}  
*—statistical significance between the groups based on the one-way ANOVA or equivalent nonparametric test; BMI—body mass index; ES—effect size; nP—total number of participants; nF—number of females; nM—number of males; SD—standard deviation; SC—strength and conditioning.  
\end{table}