Relationship Between Anthropometric and Physiological Characteristics in Youth Soccer Players

To the Editor: The Yo-Yo Intermittent Endurance Test (YYIE) is a maximal aerobic fitness test. It is a helpful instrument to follow up the player's endurance capacity throughout the season. Two YYIE versions are available: level 1 was designed to test youth and amateur athletes, whereas level 2 was developed to test well-trained athletes (1,2). We read with interest the article from Wong and colleagues (3) regarding the relationship between anthropometric and physiological characteristics of U14 Hong Kong soccer players. The authors evaluated the intermittent endurance performance using YYIE2, and no significant differences were found between field positions. We noted the high average values reported (ranging 1548 ± 695 m for goalkeepers and 2283 ± 780 m for midfielders). These values are considerably higher than others observed in elite Portuguese U19 (1458 ± 422 m) (4), adult male recreational soccer players (1160 ± 140 m) (5), elite female Danish (1265 ± 133 m) (6), and professional Portuguese male players (1412 ± 407 m) (7). However, the reported values are similar to those reported in maturity-controlled 14–15 year-old Portuguese players (ranging 1473–2655 m) when using the YYIE1 (8). Others used YYIE1 in youth soccer players and observed average values of 2556 ± 912 m in U14 Portuguese players (9), 3044 ± 442 m in 16 year-old Italian players (2), and 2761 ± 716 m in U14 Chinese soccer players (10). From our experience as soccer fitness coaches, very few adult professional players attain such high values in YYIE2 when the guidelines established by Bangsbo (1) are strictly followed. Many on-the-field fitness coaches prefer to continue the test until complete exhaustion even if the player fails to maintain the dictated speed. Therefore, we question whether the authors terminated the test when the subject twice failed to reach the front line on time. Top-class players perform more high-intensity running and sprinting during a match than moderate professional players (11), suggesting the need to establish the basic levels of fitness to play at elite standard. Although the relative importance of physiological and performance testing in the talent identification process has not been quantified (12), we agree with Wong and colleagues that a complete physiological profile of elite youth players provides templates for “talent identification, training program design, and the selection of young players to higher playing levels” (3). Therefore, it is essential that common methodologies are applied properly to provide a more comprehensive perspective of soccer training and talent development. João Brito André Seabra and António Rebelo Center of Research, Education, Innovation and Intervention in Sport, Faculty of Sport of the University of Porto, Porto, Portugal