# Maturity Status, Relative Age and Constituent Year Effects in Young Iberian Kayakers
## 1 Introduction  
In Portugal and Spain, during the various age-group competitions, different experience levels and skill may be found among the paddlers participating in the National Championship. To provide equal opportunities during competition, like in other sports systems, in kayaking, young athletes are commonly grouped by their birth year. _Maturation_ is a process that involves many body changes [1]. It plays a crucial role in improving motor skills; and maximizing motor skill proficiency is ideal in childhood. [2]. Previous research, considering performance [3], with young paddlers has focused on maturational and morphological analysis of the best athletes in their categories [4; 5; 6; 7], and reported that the most mature kayakers obtain the best performances. More recently, [PERSON] et al. [8] showed that years of practice were crucial in youth kayaking success besides maturity. Therefore, talent identification batteries must consider aspects of maturity in performance variations [9], preventing the drop out of less mature children derived from an absence of competitive success or a perceived absence of ability [10]. Meanwhile, relative age (RA) concerns a child's chronological age inside their age group and is defined by the date of birth and the cut-off selection date [11]. The relative age effect (RAE) is a frequent occurrence in youth sports [12] and is characterized by the discrepancy between athletes' observed and expected birth date distributions [13]. Thereby, children born early in the selection year have a higher probability of experiencing successful participation and maintaining it. It is important to notice that RA and biological maturation are independent constructs. RA depends on birth and cut-off dates, and biological maturation depends on genetics and environmental context. Also, there is a considerably more extensive range for variation in biological maturity in a single-year age group than in RA. While in RA, differences are limited to twelve months, maturity can differ up to six years [11]. For instance, regarding chronological age, a person born in January is nearly twelve months older than some other person born in December of the same year. Consequently, the physical and psychological differences that can be observed may perhaps be attributed to this singularity [4; 14]. Furthermore, when studying under 13 and 15 football players, [PERSON] et al. [5] stated that stature, body mass, and lean body mass were influenced by the birth date in these categories. Additionally, [PERSON] et al. [6] presented significant differences between birth months in an analysis of physical fitness test performances. Such an advantage could justify, to some extent, the bias in sports selection credited to the peculiarities of the RAE. Also, RAE may show up well before puberty, and it is more likely that these differences result from the context in which children are inserted, resulting in the possibility of experiencing different environments with implications for their development, which is probably more associated with age than maturity [7]. For that reason, almost all competitive sports are organized into age categories, presumably, to reduce such differences. Most likely, participants are grouped by chronological age to guarantee honest competition and opportunity [3]. The influence of the relative age effect phenomena is explained as influencing several sports, including swimming [15; 16], football [17], and basketball [18]. Nevertheless, reversed RAE has also been reported, like in the cases of athletics [19] and futsal [20]. Moreover, this inverse RAE has been explained in sports where performance demands high technical skills [21], and physical qualities may be secondary [22]. Regarding keyaking, the only study focusing on the RAE phenomena was conducted by [PERSON] et al. [23], pointing out that young athletes born in January, February, and March have a higher probability of being chosen for development training camps.