## 4 Discussion
Although a short DS was effective in changing musculotendinous extensibility in this study, it had no significant effect on the maximal muscle strength. In addition to the stretching volume, two other factors that can influence the DS effect are the stretching velocity and amplitude [2,17,29]. Different stretching velocities and amplitudes may change musculotendinous extensibility and maximal muscle strength. Therefore, future studies need to consider DS velocity and amplitude when comparing the effects of different amounts of DS on both musculotendinous extensibility and maximal muscle strength. Neuromuscular function is thought to improve because of increased core and muscle temperatures and increased muscle activity during the maximum voluntary contraction [9]. As a stretch that benefits from active and rhythmic muscle contraction, DS helps warm up and increases heart rate, core temperature, and muscle temperature [2]. Additional warm-up time increases the muscle temperature [41]. Previous studies have reported that an increase in muscle temperature increases nerve conduction velocity and improves athletic performance [41] and that an increase in muscle temperature of 1 \({}^{\circ}\)C increases athletic performance by 2-5% [42]. Therefore, an increase in the neuromuscular function and muscle activity may have occurred. Consequently, an increase in the muscle temperature may positively affect athletic performance. The present study suggests that an increase in the muscle temperature counteracted the negative effects of the decreased MTS on athletic performance, such that maximal muscle strength did not change. In a survey study on stretching in sports fields, it was reported that a DS of 30 s or less per set was generally widely used and that the time required for stretching the full body was approximately nine minutes [3]. Because the warm-up and practice times before a match are limited, a shorter and more effective stretching method is required. In this study, one set of 30 s and four sets of DS decreased MTS and increased flexibility but did not decrease athletic performance. This suggests that 30 s of DS is useful as a warm-up before sports. DS may be effective for warming up several body parts within a limited time. Therefore, the results of the present study may be useful in planning DS protocols for warm-up exercises in sports. As DS is used in warm-ups before sports, its effects must be sustained and exerted at the start of a match or training session. Therefore, it is necessary to clarify the sustained effects of DS. Several studies have reported the long-term effects of DS; however, the evidence is insufficient. One study showed that the effects of DS on the ROM and passive stiffness lasted for >90 min, whereas the peak passive torque returned to baseline within 30 min [7]. Another study showed that the ROM and peak passive torque persisted for 60 min after DS [43]. Future studies should investigate the sustained effects of varying amounts of DS. This study had some limitations. First, we did not set control conditions that included either aerobic or dynamic stretching. Pre-stretching aerobic exercise may have affected our results; however, it is unclear whether this effect was due to aerobic exercise or DS. Musculotendinous extensibility may also be affected by aerobic exercise. Second, we did not investigate physiological outcomes, such as muscle blood flow or nerve conduction velocity. Although DS improves performance by improving neuromuscular function, the details of this mechanism remain unclear. Third, we investigated only the acute effects of DS. Examining the sustained effects will help to clarify the appropriate timing for DS. Fourth, we performed MVICs before the post-measurements of musculotendinous extensibility and muscle strength. A previous study reported that MVICs altered the mechanical properties of musculotendinous complexes [44]. Therefore, MVICs pre-stretching may affect musculotendinous extensibility and maximal muscle strength.