The aim of the present study was to determine metabolic responses, movement patterns and distance covered at running speeds corresponding to fixed blood lactate concentrations (FBL_s) in young soccer players during a match play. A further aim of the study was to evaluate the relationships between FBL_s, maximal oxygen consumption (VO₂max) and distance covered during a game. A multistage field test was administered to 32 players to determine FBL_s and VO₂max. Blood lactate (LA), heart rate (HR) and rate of perceived exertion (RPE) responses were obtained from 36 players during tournament matches filmed using six fixed cameras. Images were transferred to a computer, for calibration and synchronization. In all players, values for LA and HR were higher and RPE lower during the 1^st half compared to the 2^nd half of the matches (p < 0.01). Players in forward positions had higher LA levels than defenders, but HR and RPE values were similar between playing positions. Total distance and distance covered in jogging, low-moderate-high intensity running and low intensity sprint were higher during the 1^st half (p < 0.01). In the 1^st half, players also ran longer distances at FBL_s [p<0.01; average running speed at 2mmol·L^-1 (FBL₂): 3.32 ± 0.31m·s^-1 and average running speed at 4mmol·L^-1 (FBL₄): 3.91 ± 0.25m·s^-1]. There was a significant difference between playing positions in distance covered at different running speeds (p < 0.05). However, when distance covered was expressed as FBL_s, the players ran similar distances. In addition, relationships between FBL_s and total distance covered were significant (r = 0.482 to 0.570; p < 0.01). In conclusion, these findings demonstrated that young soccer players experienced higher internal load during the 1^st half of a game compared to the 2^nd half. Furthermore, although movement patterns of players differed between playing positions, all players experienced a similar physiological stress throughout the game. Finally, total distance covered was associated to fixed blood lactate concentrations during play.

• Based on LA, HR and RPE responses, young top soccer players experienced a higher physiological stress during the 1 half of the matches compared to the 2 half.

• Movement patterns differed in accordance with the players' positions but that all players experienced a similar physiological stress during match play.

• Approximately one quarter of total distance was covered at speeds that exceeded the 4 mmol·L fixed LA threshold.

• Total distance covered was influenced by running speeds at fixed lactate concentrations in young soccer players during match play.