## 4 Discussion
Our results suggest that changes in ROM and stiffness cannot be detected with these ultrasound measurements [24]. Our results for foam rolling agreed with other studies that found foam rolling to have little or no impact on muscle characteristics [36] or performance measures [28; 32; 37]. There were no changes in any of the muscle characteristics, and this is in agreement with [PERSON] et al. [27], but it contradicts [PERSON] et al. [37], who reported an increase in muscle thickness following foam rolling. Evidence that foam rolling increases muscle size by increased tissue hydration and blood flow [10; 37] was not observed in our study. There were no increases in muscle size or echo intensity following foam rolling. Foam rolling has been speculated to improve force production by stimulating the neural system to increase its firing rate and recruitment patterning [10]; however, we did not see improvement in any of the isometric strength measurements or muscle activation, which is similar to other findings [49; 59]. When addressing the sex difference, our results indicate that there were no differences between males and females on how they respond to foam rolling. This contradicts the results of [PERSON] et al. [49] who reported that there was an increase in peak force output for males but not females following foam rolling. They attributed these results to muscle mass differences. For percussion massage, the results of this study build upon previous research [11; 39; 43; 44]. There were no changes in performance testing, force output, or muscle activation following percussion massage. However, the results also contradict the findings of studies that found increases in horizontal jumping test, T drill test, balance measurements, and peak torque [41; 42]. Percussion massage is believed to increase blood flow to the muscle, which could lead to increases in performance, but we did not observe any changes in muscle size or echo intensity that would lead us to believe there was an increase in blood flow to the muscle. This is different than what has been previously reported in the literature [36] that percussion massage increases muscle thickness. Overall, percussion massage had no effect on any muscle characteristics or performance outcome. One result of this study that was significant was the size and strength differences between males and females, with males having a larger cross-sectional area, pennation angle, and peak torque. These are similar to other findings that demonstrate differences in muscle mass (14 vs. 11.5 cm\({}^{2}\), respectively) [46] and strength [47] between sexes. [PERSON] et al. [47] reported an average 60% decrease in strength from males to females; this study's average difference in peak torque was ~55%. These differences in males versus females are reduced when normalizing strength values to muscle size [60; 61]. Although these findings support the differences between sexes, the novelty of this study is that both sexes respond similarly to the modalities. This indicates that muscle size or strength has little effect on how one would respond to these soft-tissue modalities. This furthers the research that has demonstrated no sex difference in muscle properties [62] or in response to stretching [63]. This contradicts previously reported [49] results that males and females have different responses to soft-tissue modalities. However, the results of this study and the summation of previous literature indicate that there is no sex difference in response to soft-tissue modalities. There are limitations to this study, as most of the modality research is focused on increasing ROM. This study did not measure ROM, so we cannot confirm that our protocol increased ROM. Our protocol consisted of five minutes in duration, which matched or exceeded other studies that had shown increases in ROM. Static stretching was greater than 1 min [4], foam rolling was two minutes [28], and percussion massage was five minutes [11], and in other studies, these have been shown to increase ROM.