## 1 Introduction  
Field Hockey (FH) is a field-invasive game that requires a good combination of aerobic fitness, anaerobic power, and technical skills [1, 2]. In addition, agility represents a key factor for the development of technical skills such as dribbling or defensive drills. Agility can be defined as the quickness by which an athlete can change direction and includes complete decelerations and quick accelerations [3]. Despite the importance of this element in FH, interestingly, no significant differences in agility and sprint performances were detected between division I and division II Italian players [4].  
Muscle architecture has been proposed as one of the most important determinants of muscle performance [5]. Some studies reported significant correlations (r = 0.51\(-\)0.71) between the muscle morphology of the vastus lateralis and dynamic performances such as a 100 m sprint [6] or sprint performance on a non-motorized treadmill [7]. Significant correlations (r = 0.54) have been also detected between the muscle morphology of the gastrocnemius and the sprint performance in competitive sprinters [8]. Furthermore, significant correlations were found between the muscle morphology of the vastus lateralis and the isokinetic torque expressed at high angular velocity (r = 0.55) [9], and between the muscle thickness of the pectoral muscle and the bench press 1 repetition maximum (1 RM; r = 0.83) [10]. Despite muscle size significantly influences muscle strength [11], other parameters such as the pennation angle (PA) and fascicle lengths (FL) appear more related to dynamic performances and power [5]. Indeed, large correlations have been reported between the sprint abilities and the FL of the vastus lateralis (VL) in sprinters [8]. In addition, greater FL and lower PA have been measured in Australian Football Players compared to endurance athletes [12]. Furthermore, [PERSON] et al. [13] reported large correlations between the muscle thickness (MT) and FL of VL and the peak rate of force development (pRFD) produced at an isometric leg press by young male and female track and field throwers. Finally, [PERSON] et al. [14] showed large correlations between the front crawl sprint swimming performance and the FL of the vastus lateralis in young swimmers. Even though several investigations underlined the role of both FL and PA for dynamic performances in several sports, surprisingly, to the best of our knowledge, only one study to date investigated the relationships between agility and muscle architecture of VL [15]. Those authors reported negative correlations between PA and agility performance, while no correlations were detected between FL and agility in badminton players.  
To date, no studies have investigated the relationships between muscle architecture and maximal strength, power and agility performances in FH players. Thus, the aim of the present investigation was to study the relationships between muscle architecture of VL and athletic performance in high-level FH players. Further information on the relationships between muscle morphology and dynamic performances (including agility), may represent a step further toward a better understanding of the relationships between muscle architecture and performance in competitive athletes.