## 1 Introduction
Overall, the effects of static stretching on muscle remain unclear, even via ultrasound measurements. Another common type of soft-tissue modality is self-myofasical release with the use of a foam roller. It is more commonly referred to as \"foam rolling\", which involves placing your body weight on a dense foam roller and producing continuous motion up and down the full length of the muscle while placing your hands on the ground for support [28]. The aim of foam rolling is to decrease pain and improve the pliability of the fascia, which is a complex network of connective tissue throughout the entire body [29]. Foam rolling has shown increases in ROM of 4-10\({}^{\circ}\)[28; 30], without the negative effects seen with static stretching [28; 31]. [PERSON] et al. [30] stated that foam rolling can improve the vertical jumping performance along with muscle activation. However, the effects on performance are mixed as [PERSON] et al. [32] reported that foam rolling had no impact on performance (vertical jump height and power, isometric force, and agility), but could reduce the \"feeling\" of fatigue. The justification for foam rolling as part of a warmup routine is based on the claims that foam rolling may increase tissue compliance [33], increase tissue water content [34], and/or improved neuromuscular function [10] and increase blood flow [35]. If there are changes in the muscle, one might expect these to be present in ultrasound images. [PERSON] et al. [36] set out to determine this by measuring changes in pennation angle, muscle thickness, and cross-sectional area; they did not observe any changes in pennation angle, but observed a decrease in cross-sectional area following two minutes of foam rolling. This is contradictory to [PERSON] et al. [37] who reported an increase in muscle thickness after three minutes of foam rolling. They speculated this as acute muscle swelling (increase blood flow and water content). [PERSON] et al. [38] observed 6-7\({}^{\circ}\) reductions in pennation angle following 7 weeks of foam rolling. They did not give a reason for why these changes took place, and angle was the only reported variable. Another proposed reason to foam roll is to increase blood flow [10]; however, no research has evaluated this idea. Similar to foam rolling, percussion massage is a form of vibrational therapy that falls under the grouping of self-myofasical release modalities [39]. Vibrational therapy in this context refers to a hand-held piece of equipment called a percussion massage gun that massages the muscle by rapidly vibrating the muscle using different attachments meant to target different muscles or connective tissues [40].Vibrational therapy has been shown to improve range of motion and increase muscle performance (horizontal jumping, \(t\)-test, balance, peak torque) by 4-7% [41; 42]. Multiple studies have found that using vibrational therapy pre-exercise leads to no change in performance testing, force output, or muscle activation [11; 39; 40; 43; 44]. Due to the mixed results of previous research, it is still unclear if percussion massage influences performance in a positive way or not at all. Percussion massage has been shown to increase muscle thickness following two minutes of intervention [36], and this contributes to tissue hydration. [PERSON] et al. [45] observed changes in muscle thickness (11 mm) for those who reported a negative response (increase in muscle soreness) to 20 min of percussion massage, but there were no changes in pennation angle. Changes in muscle thickness have contributed to an increase in blood flow (acute swelling/tissue hydration) [45] following percussive massage. Echo intensity is also affected by blood flow and swelling, so it may be another marker of percussion-reduced swelling; however, no studies have analyzed whether echo intensity values change following percussion massage. One other aspect that is missing from the literature is the effect of these modalities between sexes.