Variability of objective and subjective intensities during ball drills in youth soccer players

The aim of this study was to examine the intrasubject (intraclass coefficient correlation [ICC]) and intersubject variability (coefficient of variation [CV]) of soccer ball drills (BD) involving or not opposition in male youth soccer. For this purpose, a collective ball dribbling (DB) exercise and a 7-a-side ball game without coach encouragements were considered. Exercise intensity was assessed as heart rate (HR), training load (TL), and perceived exertion scales. Fourteen U-14 male soccer players (age, 14.79 ± 0.43 years and experience, 6.5 years) of a Spanish First Division club academy participated in the study. Ball drills were examined for variability over 5 successive training sessions in similar field conditions. Results showed that 7-a-side was significantly (p = 0.000) more demanding than DB. Indeed the TL, HRmax, HRmean, overall perceived exertion, and leg muscular perceived exertion (MPE) resulted 141, 8.7, 11, 56, and 72%, higher in 7-a-side than in DB, respectively. In the 7-a-side condition, good intersubject (CV < 10%) and low intrasubject (ICC < 0.7) variability were observed. In the DB condition, CVs were below 10% CV only for HR variables and the ICC values were higher than 0.7 only for MPE. Despite the moderate reproducibility of BD not considering opponents, this condition did not reveal to induce homogeneous physiological responses in young soccer players. Therefore, the use of this kind of drills may be questionable when considered as alternative of moderate intensity generic aerobic training. Despite the higher interaction between players variability in the opposition drills resulted lower, this suggests their use as a specific conditioning exercise.