# Influences of Sex on Muscle Architecture and Performance in Elite Field Hockey Players
## 1 Introduction  
Field Hockey is a fast moving, territorial game in which power and sprint capabilities represent key factors to support the success of players at the international level [1]. Although a relevant variability exists between the different field positions and sexes, strength and power of both the upper and the lower body have been indicated as important contributors for essential skills such as the drag flick and sprint [2].  
Differences in strength and power between men and women have been widely investigated in both trained [3, 4] and untrained individuals [5]. Women are known to be less strong and powerful than men, especially in the upper body [4, 5]. However, these disparities become less evident when strength is considered in relation to lean body mass or muscle architecture [6]. Recently, muscle ultrasound has been used to investigate the relationships between muscle architecture and performance in male Field Hockey players competing at the national level [7]. Significant correlations between muscle architecture of vastus lateralis and sprint and change of direction capabilities were reported by these authors (\(r\) = 0.5; \(p\) = 0.034 and \(r\) = 0.62; \(p\) = 0.006, between fascicle length and sprint and change of direction, respectively). Unfortunately, in that study, echo intensity (EI) was not considered. This parameter, calculated by the darkness of the ultrasound image [8], has been recently indicated as a strong predictor of muscle quality [9, 10]. [PERSON] and colleagues [11] reported significant correlations between EI, sprint performance, and strength,in track and field athletes. EI is influenced by the characteristics of both contractile and noncontractile components of muscles [12] and by the training status. Although aging has been associated with increased EI levels [13], training tends to reduce this parameter at any age [14]. An elevation in EI in trained athletes has been associated with reduced functionality and may increase the chance of muscle injuries [15]. Some studies have reported higher values of EI (indicating a lower muscle quality) of the vastus lateralis in women compared to men (71.2 \(\pm\) 12.8 and 60.4 \(\pm\) 12.6 in women and men, respectively) [10]. However, other studies conducted on middle-aged and old individuals did not find significant differences in EI between the sexes [16].  
Although some studies have investigated the differences in muscle architecture and EI between men and women, only a few considered highly trained individuals [3,7] and, to the best of our knowledge, none have been conducted on elite Field Hockey players of both sexes. Thus, the first aim of the present study was to compare male and female elite Field Hockey players for muscle architecture, EI, strength and power, and sprint and change of direction performance. A second aim of the present study was to investigate the relationships between muscle architecture and performance in elite Field Hockey players. Since sex is known to influence muscle adaptations to sport training and muscle quality, the authors hypothesize that significant differences may also exist in EI between male and female elite Field Hockey players. The authors also hypothesized that EI may be significantly correlated with strength and power performance in both male and female players.