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Time-motion analyses and physiological measurements were performed to investigate the physiological demands of football referees (n = 15) and assistant referees (n = 15) in international games and to examine whether high-intensity running (HIR) correlates to the referees' ability to keep up with play. Total distance covered (10.27 +/- 0.90 vs. 6.76 +/- 0.83 km) and HIR (1.92 +/- 0.58 vs. 0.97 +/- 0.22 km) was higher (P < 0.05) for referees than assistant referees, while sprinting distance was not different. Referees covered 0.89 +/- 0.37 km by backwards running and assistant referees covered 1.54 +/- 0.66 km by sideways running. Mean heart rate was higher (P < 0.05) for referees than assistant referees (150 +/- 3 vs. 123 +/- 3 b.p.m.), whereas blood lactate was not different. Backwards/sideways running decreased (P < 0.05) from the first to the last 15-min period for referees (49%) and assistant referees (42%), whereas HIR was unaltered. HIR was inversely correlated with the five highest distances from infringements in both halves (r = -0.60 and -0.58, P < 0.05). In conclusion, international match officials carry out an important amount of HIR throughout games, while low-intensity and unorthodox running activities are reduced during games. Referees performing the most high-intensity work are better to keep up with play. The match activities differ significantly between referees and assistant referees, which should be considered in training and testing procedures.
Krustrup et al. (Mon,) studied this question.