Relationships Between Measures of Physical Fitness Change When Age-Dependent Bias is Removed in a Group of Young Male Soccer Players.

James, RS, Thake, CD, and Birch, SL. Relationships between measures of physical fitness change when age-dependent bias is removed in a group of young male soccer players. J Strength Cond Res 31(8): 2100-2109, 2017-Age-dependent bias is a key issue within talent identification of children, particularly when measures of physical fitness are used. Coaches in sport would benefit from a relatively straightforward method to remove age-dependent bias, enabling identification of children who are relatively high performers for their age. This study aimed to determine whether removal of age effects caused changes in the relationships between physical performance and anthropometric measures commonly used in talent identification and development systems. Sixty male soccer players, aged 11-17 years, underwent measures of anthropometry, muscular power, strength, sprint speed, and agility. Most absolute measures of performance were significantly correlated with each other, and all performance measures were significantly correlated with age. Age residuals were calculated, for all variables, to determine which players performed relatively well for their age and to investigate age-independent relationships between variables. In general, players with relatively fast sprint performance for their age were taller and had relatively high performance in jump power output and grip strength for their age (r > 0.25 and p < 0.025 in each case). Absolute sprint performance PC1 was significantly correlated with absolute agility performance PC1 (r = 0.473, p < 0.001). However, there was no significant relationship between age-independent measures of agility and any other measures. Usage of age residuals highlights performers that have relatively high physical fitness for their age. Such analyses may assist the talent identification and development processes as long as differential rates of physical development between players are also considered.