## 1 Introduction  
Basketball is a physically demanding sport, which requires players to participate in repeated bouts of intense actions (e.g., sprinting, shuffling, and jumping) interspersed with short low-intensity actions (e.g., walking, jogging) and recovery [1, 2, 3, 4, 5]. As a result, basketball players develop several fitness attributes, including muscular power [6, 7, 5], speed [6, 8] and agility [7, 8]. Body size (i.e., height, body mass) and body composition also appear to be determinants for adult [9, 10, 11] and youth basketball performance [12, 13, 14].  
The relationships between body composition (BC) and performance tests have been studied in several sports [15, 16, 17, 18], and previous research has shown that body fat percentage (BF%) and fat-free mass (FFM) levels (two common indicators of body composition) varied according to the sport and sport-specific success [15], particularly in basketball [19]. In a recent study with female college athletes from six different sports (basketball, volleyball, gymnastics, lacrosse, rowing, and soccer), gymnastics and basketball athletes displayed the lowest BF% across the six sports, while basketball players had the highest FFM of all sports [15]. Other studies found that long-distance runners were characterized by relatively low BF% and low FFM [20], throwers had high body adiposity and a high level of FFM, while swimmers demonstrated higher values of body fat [21]. Previous studies found that increased BF% was negatively correlated with total minutes played by ice hockey players [22] and with the running performance of top-class runners [20]. In the meantime, increased FFM was positively correlated with the power clean test of lacrosse college players [23]. It has also been shown that a high FFM predicted strength and power performance in highly trained football athletes [24]. In youth basketball, BF% was negatively correlated with speed, agility, and anaerobic tests performed with and without a ball [8]. The overweight U-12 players showed worse performance in running (sprint and endurance) and jumping (CM)), while U-18 overweight practitioners had worse endurance than normal-weight players [25].  
Besides influencing physical test results, BC also has a strong impact on game performance and players' competitive level. A recent meta-analysis pointed out that BF varies according to players' competitive level, with international players showing less BF than regional players [19]. A previous study with Portuguese U-14 players selected for regional teams revealed that athletes from lower-ranked teams had higher values of BF% than those from finalist teams, suggesting that BF could influence the team's final classification [12]. In basketball, previous studies have assessed the players' game performance through the performance index rating (PIR) and points scored per game [13; 14]. The knowledge of the relationship between BC and on-court and physical test performance may help coaches to guide the training program and help with players' athletic success. In basketball, where body size (i.e., body mass and height) is definitively an advantage, the athletes tend to be taller, heavier and have a larger FFM than other athletes [5; 21]. Previous research has evaluated the ideal physiological and anthropometric profiles of successful adult and professional basketball players [9; 11]. However, no study relating BC with fitness tests and on-court performance has been conducted in youth basketball.  
In accordance, the purpose of this study was to clarify the impact that BF% and FFM have on conditioning test results (i.e., speed, agility, upper and lower body strength) as well as on players' on-court performance, evaluated by PIR and points per game (PPG) in U-14 elite Portuguese basketball players. It was hypothesized that BF% and FFM would play a significant role in fitness test results and on-court performance, with lower BF% and higher FFM players showing better physical test results and higher PIR than higher BF% players.