## 3 Results
\begin{table}
\begin{tabular}{c c c c c} \hline
**Pretension (MVIC\%)** & \multicolumn{2}{c}{**50\%**} & \multicolumn{2}{c}{**100\%**} \\ \hline
**Stretching Energy (J)** & **20** & **100** & **20** & **100** \\ \hline Eccentric mechanical work (J) & 18.9 \(\pm\) 0.1 & 98.1 \(\pm\) 0.2 & 19.2 \(\pm\) 0.1 & 98.5 \(\pm\) 0.2 \\ Concentric mechanical work (J) & 22.4 \(\pm\) 2.0 \({}^{\text{c}}\) & 69.9 \(\pm\) 6.9 & 18.7 \(\pm\) 0.7 \({}^{\text{a}}\) & 62.8 \(\pm\) 11.4 \\ Mechanical efficiency (\(\eta\)\%) & 53.92 \(\pm\) 2.2 \({}^{\text{b,c,d}}\) & 42.83 \(\pm\) 2.13 \({}^{\text{a,c}}\) & 49.38 \(\pm\) 0.93 \({}^{\text{a,b,d}}\) & 39.59 \(\pm\) 6.21 \({}^{\text{a,c}}\) \\ Peak torque (N-m) & 131.42 \(\pm\) 9.80 \({}^{\text{b,d}}\) & 208.62 \(\pm\) 25.64 \({}^{\text{a,c}}\) & 135.85 \(\pm\) 14.86 \({}^{\text{b,d}}\) & 204.87 \(\pm\) 19.33 \({}^{\text{a,c}}\) \\ Knee flexion (\({}^{\text{c}}\)) & 12.26 \(\pm\) 1.86 \({}^{\text{b,c,d}}\) & 37.95 \(\pm\) 2.49 \({}^{\text{a,c}}\) & 10.17 \(\pm\) 1.55 \({}^{\text{a,b,d}}\) & 37.67 \(\pm\) 6.0 \({}^{\text{a,c}}\) \\ Peak tendon force (N) & 3379 \(\pm\) 918 \({}^{\text{b,d}}\) & 6213 \(\pm\) 1574 \({}^{\text{a,c}}\) & 3417 \(\pm\) 699 \({}^{\text{b,d}}\) & 5998 \(\pm\) 1227 \({}^{\text{a,c}}\) \\ Tendon stress (MPa) & 5.10 \(\pm\) 1.38 \({}^{\text{b,d}}\) & 9.30 \(\pm\) 2.08 \({}^{\text{a,c}}\) & 5.15 \(\pm\) 1.05 \({}^{\text{b,d}}\) & 9.04 \(\pm\) 1.84 \({}^{\text{a,c}}\) \\ \hline \end{tabular} Abbreviations: MVIC = maximal voluntary isometric contraction, significant difference marked with superscript letters; a: different from 50%, 20 J, b: different from 50%, 100 J, c different from 100%, 20 J, d different from 100%, 100 J condition. Significant differences were considered at \(p<0.0083\) according to Bonferroni correction for multiple pairwise comparisons.  
\end{table} 
Table 2: Mean and SD calculated mechanical variables for each contractile condition. Figure 3: The mean EMG activity during the eccentric and concentric phase of the contraction in each condition. The black vertical lines indicate the standard deviation of the corresponding mean values. Asterisks indicate significant differences. Abbreviations: BF—biceps femoris, ST—semicintonosus, VL—lateral vastus, VM—medial vastus. 100 J load. Similarly, the vastus lateralis muscle exhibited lower mean EMG activity under the same conditions but during the concentric phase of contraction. The correlation analysis indicated a significant relationship between the patellar tendon cross-sectional area and ME during SSC contractions with a 20 J stretch load at both 50% and 100% pretension levels (Figure 4). In contrast, neither the resting length of the patellar tendon nor AmAt showed any association with ME (Figure 4). Peak tendon force showed no significant correlation with ME nor any of the morphological parameters of the quadriceps MTU. The estimated tendon stress during SSC contraction also showed no association with ME nor with the morphological parameters of the quadriceps MTU. The maximal force generation capacity (MVC 30\({}^{\circ}\)) showed no correlation with the muscle volume (r = 0.18, \(p\) = 0.65) and the PCSA (r = 0.01, \(p\) = 0.99) of the quadriceps femoris mean patella tendon CSA (r = 0.09, \(p\) = 0.81), but showed large association with knee flexion in all but one SSC condition (r = \(-\)0.88, \(p\) = 0.0018, r = 0.01, \(p\) = 0.98, r = \(-\)0.88, \(p\) = 0.0015, r = \(-\)0.92, \(p\) = 0.0004).