# Muscle Activity of Superimposed Vibration in Suspended Kneeling Rollout
## 1 Introduction
Similarly, [PERSON] and associates [17] stated that the vibration direction affects muscle activation. In their study, higher muscle activity was observed when vibration was perpendicularly transmitted to the target muscles. Research on new challenging strength and conditioning methods combining different demanding sources has led to vibration superimposition onto unstable devices. Observing the acute effects of superimposing vibration, [PERSON] and [PERSON] [18] compared the muscle activation of the gastrocnemius medialis, vastus medialis oblique, vastus lateralis, rectus abdominis, and multifidus muscles, with athletes performing an isometric half squat in four different stable and vibrating conditions; thus, the researchers observed significant increases on a wobble board at 30 Hz. Moreover, [PERSON] and associates [19] compared the muscle activation of a Bulgarian squat under four conditions: (1) with the back foot on a brach and the front foot on the floor, (2) with the back foot on a TRX(r) and the front foot on the floor, (3) with the back foot on a TRX(r) and the front foot on a BOSU(r), and (4) with the back foot on a TRX(r) and the front foot on a WBV platform. Results showed that the use of a TRX(r) is not sufficient to increase muscle activation (rectus femoris, biceps femoris, gluteus medius, vastus medialis, and vastus lateralis of the front leg; and rectus femoris of the rear leg); however, combining the use of a BOSU(r) or a vibrating platform increased the activity of the analysed muscles. Recently, a new vibratory device placed at the anchor point of a suspension strap has been developed. [PERSON] and associates [20] compared the muscle activity (rectus femoris, biceps femoris, semitendinos, gluteus maximus, and gastrocnemius medialis and lateralis) in a supine bridge and a hamstring curl exercise without vibration, and with vibration at 25 Hz and 40 Hz and 8 mm of amplitude. A significantly higher muscle activity was observed in the musculature closest to the vibration exposure point at 25 Hz. Similarly, [PERSON] and associates [21] analysed the activity of the dominant upper-limb musculature, as well as the external oblique, under three conditions: (1) non-vibration, (2) vibration at 25 Hz, and (3) vibration at 40 Hz. Results showed higher muscle activity in the external oblique, triceps brachii, anterior deltoid, and clavicular portion of the pectoralis major at 40 Hz. In addition, the external oblique and anterior deltoid muscles also showed significant increases at 25 Hz, and the sternal portion of the pectoralis major showed higher activity at 25 Hz. Kneeling rollout is considered a core exercise [22; 23; 24] that can be performed using suspension devices. The use of an ab wheel [25; 26; 27], a Swiss ball [28; 29], a suspension device [30; 31], and placing the hands on the ground while maintaining their position [31] have been reported in the literature. All these authors analysed the core muscles, obtaining the highest values for the rectus abdominis, closely followed by the external oblique, and much lower values for the lumbar paraspinal muscles. To the best of our knowledge, no previous studies have considered kneeling rollout as an overhead action, recording the muscular activity of the periscapular muscles in this position, which has been considered a risky position for the glenohumeral joint and is often repeated in throwing sports actions. Therefore, the aim of the present study was to compare the pectoralis sternalis and clavicularis, anterior deltoid, serratus anterior, latissimus dorsi, and infraspinatus activity when performing a kneeling rollout taking a suspension strap, between the non-vibration condition and vibration at 25 Hz and at 40 Hz. It is hypothesised that superimposing vibration at the higher frequency (40 Hz) will increase muscle activation compared to the other two conditions. It is also hypothesised that the highest vibration condition will be scored as the most demanding in the OMNI-Res scale, when compared to the lower frequency and the non-vibration condition.