# Influence of Category and Sex in Game Structure Variables in Young Elite Tennis
## 1 Introduction
However, among professionals, men displayed shorter point durations (4.4-7.0 s for males; 7.0-7.2 s for females) [20; 21; 26; 27; 28; 29; 30; 31; 32]. In terms of active time percentage, significant differences were reported across male categories (26.3% in U-12; 27.6% in U-14; 33.6% in U-16; and 21.9% in U-18) [19; 20; 21; 22]. However, no significant differences were found across sex or competitive levels [19; 20; 21; 22; 23; 26; 31; 33; 34; 35; 36; 37]. Regarding the number of sets per match, differences were observed in the U-18 category (2.2 for males; 2.3 for females) and in professional three-set matches (2.3-2.6), though similarities were noted when analyzed by sex [18; 24; 38]. When it comes to the number of games per set, this metric has been analyzed exclusively in professional players, revealing general differences (9.8 for males; 9.3 for females), as well as surface-specific differences: hard courts (9.6-9.9 for males; 9.2-9.3 for females), grass (10.1 for males; 9.6 for females), and clay (9.6 for males; 9.1 for females). Additional differences were observed for matches at sea level (10.1 on hard court; 9.9 on clay) and high altitude (9.9 on hard court; 10.1 on clay) in male professionals [38; 39]. In terms of points per game, male professionals recorded similar values across surfaces: clay (6.3), grass (6.0), and hard court (6.2) [40]. Sex-based differences were found in general (6.3 for males; 6.5 for females), on hard court (6.3-6.4 for males; 6.5-6.6 for females), clay (6.4 for males; 6.6 for females), and grass (6.1 for males; 6.4 for females) [39]. As for strokes per point, average values ranged from 2.5 to 5.9 in formative stages [19; 20; 22; 23; 33; 41]. A comparative study on hard courts between professionals and U-18 players found no significant differences (5.0 for professional males; 4.8 for U-18 males; 4.6 for professional females; 4.4 for U-18 females) [41]. U-18 females also showed similar averages on hard (2.7) and clay courts (2.5) [19; 33], both lower than those seen in professional females on hard court (4.4) [41]. Sex comparisons revealed similar stroke counts on hard courts in U-16 (5.4 for males; 5.9 for females) [22] and U-14 (4.8-5.3 for males; 4.3 for females) [21; 29], contrasting with U-12 males (5.7) [20]. Regarding stroke frequency (strokes per minute), professional data indicate significant differences based on sex and surface. Males demonstrated a higher frequency (44.5) than females (42.9). Stroke frequency was also higher on grass courts (45.1 for males; 44.1 for females) than on hard courts (44.0 for males; 42.2 for females) [26]. From an age and sex perspective, U-14 male players exhibited more demanding performance indicators. This aligns with the developmental stage corresponding to early and mid-puberty (ages 12-16 for males; 10-14 for females), which directly influences physiological variables [42] and plays a critical role in determining success through superior physical-motor performance in both upper and lower body segments [43]. Specifically, regarding the transition from U-12 to U-14, studies on physical conditioning report increases in strength, speed, and agility with age. Sex-wise, similar values were observed during early and mid-puberty, though a marked increase in physical capacities emerged in males once puberty had concluded [44; 45; 46; 47; 48; 49; 50; 51]. In summary, the review of previous studies across different categories and sex during the formative stages reveals a notable lack of research focused on the youngest age groups (Table 1). Therefore, the objective of this study was to analyze the temporal and structural aspects of gameplay by sex in the U-12 and U-14 categories. It was hypothesized that performance differences would be primarily determined by category and would persist across sex.