Match internal load in youth elite soccer players is period, playing position and intermittent running capacity dependent

Aims: The aims of this study were: i) to verify whether player internal load (PIL) monitored via heart rate (HR) varies with game-time and playing position; ii) whether intermittent running capacity (IRC) is related to the maintenance of within-match PIL in elite youth (U-15) soccer players. Method: Twenty-one elite soccer players (14±0.5 yrs, 172±7 cm, 63±6 kg) had their heart rate monitored (beats/min) in five matches and were tested twice for IRC (Yo-YoIR2, distance [m]) over a seven-week competitive season. Percentage of maximal heart rate (%HRmax) and time spent (TS%) in five zones (Z1[ 96%]) were our PIL indexes. Data from three complete games in the same position of each player were analyzed and matches halves, time intervals (T1 to T6), and playing positions (fullbacks, central defenders and forwards [N=5 each], midfielders [N=6]) were compared, and the relationship between IRC and within-match PIL was determined. Results: PIL was higher in 1st (86±3%) than in the 2nd half (84±4%; p<.001). The 2nd half had more TS% in Z1 and Z2 (p<.05). PIL in T4 was the lowest (p<.01), and in T6, it was lower than T1 and T2 (p<.01). Fullbacks and midfielders showed higher PIL and higher TS% in Z4 (p<.05) than the other positional roles. The average IRC correlated with PIL in T6 (r=.56, p<.01) only. Conclusion: In conclusion, the internal load in elite youth (U-15) soccer players varies with game-time and playing position; and their IRC is related to the maintenance of within-match PIL.