# Muscle Activity of Superimposed Vibration in Suspended Kneeling Rollout
## 1 Introduction  
Functional training has spread among the active population over the last few years, with the performance of individualised, perturbative, and challenging exercises [1]. Thus, the use of unstable environments has become popular and is recommended to prepare the athletes for these kinds of actions [2, 3] and might be appropriate for athletes performing high-intensity upper-body actions such as throwing or hitting balls with precision (i.e., for the sports of volleyball, tennis, water polo, handball, basketball...) [4]. In this vein, unstable environments created using Swiss balls, BOSU\({}^{\text{\textregistered}}\), TRX\({}^{\text{\textregistered}}\), Freeman plates, or T-Bow\({}^{\text{\textregistered}}\) alter the muscle activity when performing different upper-body tasks. One of the most populardevices is the suspension strap, which is mainly represented by the TRX(r) brand. These devices require only one anchor point to be fixed, and allow the athlete to perform several exercises based on body weight [5]. Suspension training has been shown to increase muscle activation compared with the traditional equivalent in most muscle groups in different training tasks [6]. Beyond this increased global activation, core muscles seem to be the most activated under suspended conditions [6; 7]. In this vein, one of the most studied exercises in suspension training is the push-up, which creates a greater muscle activation in the triceps brachii, posterior deltoid, and core muscles [7]. However, to challenge the pectoralis and anterior deltoid, it is advisable to use more stable conditions [7; 8]. Beyond the use of unstable devices in resistance training, whole-body vibration (WBV) has been suggested as an effective alternative method for enhancing the neuromuscular system [9; 10]. In the early 2000s, [PERSON] and [PERSON] [11] warned of the need to explore the use of mechanical vibration in strength training programs. In their narrative review, the authors stated that vibration involuntarily increases muscle activity because of the damper effect that the soft tissues must carry out to absorb the vertical accelerations produced by the platform. Nevertheless, in another review about this topic, [PERSON] [12] supported the use of superimposed vibratory stimulation in order to enhance explosive strength and maximum dynamic force. Moreover, although the potential neuromuscular mechanisms are similar, the author distinguished WBV and local vibration as two different training paradigms. Although WBV platforms are commonly used to stimulate lower-limb muscles, placing the hands on the platform is the simplest way to increase upper-body muscle activity through vibration [13]. [PERSON] and associates [14] recorded the muscle activation of fifteen different shoulder muscles performing press-ups and triceps dips. The muscles involved showed higher activity under vibrating conditions in both exercises. Additionally, the authors attached cables to the platform to transmit vibrations in different body and limb positions, with similar results. [PERSON] and associates [14] also compared the effects of vibration by pulling a handle while flexing the shoulder under three conditions (with the subject on top of an off WBV platform, on top of a working WBV platform, and out of a working WBV platform) and observed a higher activity of most of the studied muscles under both vibration conditions. In contrast, [PERSON] and associates [15] observed significantly increased muscle activity in the biceps brachii, triceps brachii, deltoid, and upper trapezius when performing the biceps curl, but not when performing the triceps curl and lateral raise, thus suggesting the direction of the arm movement with respect to the direction of vibration to explain such differences. Furthermore, [PERSON] and associates [16] created a vibratory bar and reported higher muscle activity in the bench press static position under the 45 Hz vibration condition. This new vibration device allows a change in the angle at which the vibration is applied.