Metabolic demands of match performance in young soccer players

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 (FBLs) in young soccer players during a match play. A further aim of the study was to evaluate the relationships between FBLs, maximal oxygen consumption (VO(2)max) and distance covered during a game. A multistage field test was administered to 32 players to determine FBLs and VO(2)max. 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 1st half compared to the 2nd 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-moderatehigh intensity running and low intensity sprint were higher during the 1st half (p < 0.01). In the 1st half, players also ran longer distances at FBLs [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 FBLs, the players ran similar distances. In addition, relationships between FBLs 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 1st half of a game compared to the 2nd 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.