## 4 Discussion  
This study compared the effects of one and four sets of DS repetitions for 30 s on musculotendinous extensibility and muscle strength and temperature. A significant increase in the maximal ankle dorsiflexion angle and muscle temperature and a significant decrease in MTS and passive torque were observed after the DS1 and DS4 sessions, regardless of the number of DS repetitions. In contrast, the isometric maximal ankle plantar flexion torque did not change after DS and did not differ between DS conditions. A significant increase and decrease in the ankle dorsiflexion angle and in the MTS and passive torque was observed, regardless of the number of DS repetitions. An increased maximal ankle dorsiflexion angle and decreased MTS have been reported after DS of four sets or ten sets of 30 s [7; 24], and the present results support these studies. The ROM is influenced by mechanical properties, such as the reduction in MTS and increase in pain tolerance [15; 24; 38]. As the MTS reflects changes in the musculotendinous complex, it does not indicate which structures, such as muscles or tendons, have changed. The changes in MTS properties after DS showed that 30 s sets of DS had the effect of lengthening tendon tissues but not muscle tissues [39]. In this study, the same changes may have occurred, and the MTS decreased after one set of DS for 30 s. Further research using ultrasonography may be required to clarify the musculotendinous complex in detail. A cycling ergometer was used for aerobic exercise before DS. In a previous study that did not find significant changes in the MTS after DS, aerobic exercise was not performed before DS [6; 15]. This may have resulted in a greater increase in muscle temperature after DS than reported in previous studies [6; 15]. Therefore, aerobic exercise before DS was considered an important factor that contributed to the different results from those of a previous study. Although DS improved musculotendinous extensibility, there was no change in the maximal isometric muscle strength. Many studies have reported improvements in athletic performance after DS [4; 5; 8; 9; 16; 17; 18]. However, in some studies, DS did not change isometric muscle strength [23; 40]. An increase in isokinetic knee flexion and extension torque was observed after DS for two sets of 30 s [9]. In contrast, no change in the maximal plantar flexion torque was observed after two 20 s sets of DS for the plantar flexor muscles [40]. A possible explanation for these discrepancies is the difference in the muscles and the repetitions of DS. [PERSON] et al. performed four different DS targeting the quadriceps and hannstrings for two sets of 30 s each, taking 6 \(\pm\) 1 min [9]. In the present study, only one set of 30 s and four sets of DS were performed on the plantar flexors, and there was no change in the maximal plantar flexion torque with either set of DS. The present study was conducted to determine the least effective durations for musculotendinous extensibility and muscle strength by comparing 30 s (one set of 30 s) and \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**One Set of DS**} & \multicolumn{3}{c}{**Four Sets of DS**} & \multirow{2}{*}{\(p\)**-Value**} \\ \hline
**Outcomes** & **Pre** & **Post** & **Pre** & **Post** & \\ \hline Peak torque & 1.81 \(\pm\) 0.23 & 1.81 \(\pm\) 0.25 & 1.83 \(\pm\) 0.26 & 1.87 \(\pm\) 0.27 & 0.198 \\ during MVIC (Nm/kg) & 33.81 \(\pm\) 0.62 & 34.55 \(\pm\) 0.59 * & 33.54 \(\pm\) 0.95 & 34.26 \(\pm\) 0.64 * & 0.145 \\ Muscle temperature (\({}^{\circ}\)C) & 33.81 \(\pm\) 0.62 & 34.55 \(\pm\) 0.59 * & 33.54 \(\pm\) 0.95 & 34.26 \(\pm\) 0.64 * & 0.145 \\ \hline \hline \end{tabular} Mean \(\pm\) standard deviation. DS: dynamic stretching; MVIC: maximal voluntary isometric contraction. * indicates a significant increase from pre-stretching (\(p<0.05\)).  
\end{table} 
Table 2: Mean (\(\pm\)standard deviation) peak torque and muscle temperature before and after stretching (n = 14). 2 min (four sets of 30 s).