# Experimental Modal Analysis of Hand-Arm Vibration in Golf: Influence of Grip Strength
## 1 Introduction  
Exposure of the human body to vibration is a well-established concern for industry. It is a source of discomfort, performance degradation, health, and safety risks [1; 2]. In this matter, the measurement of vibration doses must follow the standard practice described in [3] and [4]. Besides, European Union (EU) directive EC/2002 [5] defines the prevention and risk thresholds. In the case of hand-arm system vibration, four types of injuries may be distinguished: vascular, neurological, carpal tunnel syndrome, and repetitive strain injury [6; 7; 8; 9]. The literature also investigates the transmission of these vibrations, which is strongly correlated to body position, coupling forces [10; 11], or handle size [12]. The works that are mentioned above are also relevant in the field of sport. In 2005, [PERSON] [13] carried out a thorough study on the possible beneficial applications of vibrations in sport, such as increasing flexibility, body strength, or oxygen consumption. In tennis, vibrations that are perceived by the athletes are considered to be a key parameter for comfort [14] as well as injury risk prevention [15; 16]. In cycling, racers may undergo high levels of vibration doses [17], which are likely to cause the aneurysm of the ulnar artery [18] or paralysis of the ulnar nerve, mostly in amateur cyclists [19]. Vibrations that stem from the road profile are a determining factor in athlete's comfort [20], and thus in performance [21]. Finally, in baseball, it has been demonstrated that the mechanical characteristics of the bat are directly related to the feeling of the player [22]. Furthermore, the literature suggests that the sound of impact insports is linked to the feeling of the athletes. The sound is the image of the longer batted bat distance in baseball, [23], and the feeling is good for a loud sharp sound in golf [24]. In tennis, the sound allows for discriminating the string tension [25]. Thus, the engineering design takes account of the sound, [26]. Golf is also concerned by vibration exposure: being a sporting activity that is predominantly focused on dexterity, particular attention must be drawn to the design of the club for performance and comfort purposes. The related mechanical characteristics are widely studied in the literature, and the vibratory behavior of the club is unquestionably one of the most important. It turns out that club vibrations generated during the contact with the ball play a part in the feeling and performance of the participant. [PERSON] and [PERSON] [27] showed that vibrations of the club shaft decrease the golfer's accuracy, since they propagate up to body joints (wrist and elbow). In 2005, [PERSON] et al. [28] concluded that out of experience, golfers perceive a high dose of vibrations whenever swing is improperly executed: therefore, vibratory feedback is intimately related to performance. The influence of various mechanical parameters on the vibratory behavior was assessed in several studies, such as the effect of fixed boundary conditions, the choice of material [29], or the development of numerical models that are updated using modal analysis [30; 31]. However, to the authors' knowledge, the literature does not investigate the effect of grip strength on the vibratory behavior of a golf club, despite evidence of its ability to significantly remove the structural response in other activities [32]. Another in situ observation is that amateur players tend to apply a greater grip force on the club shaft than professional players, which could play a major role in the development of specific diseases, such as tendinitis among amateur players [33]. The aim of this paper is to complement these research studies by focusing on the grip strength and its effect on hand-arm vibration during ball contact. Section 2 of the present paper describes the standard governing the calculation of vibration doses on the human body.