Physical and physiological demands of field and assistant soccer referees during America's cup

The aim of this study was to examine the physical and physiological demands of top-class soccer field (FR; n = 7) and assistant (AR; n = 7) referees during America's Cup. The FR and AR were equipped with a global positioning system (GPS) and a heart rate (HR) monitor for the recording of displacements and cardiovascular stress, respectively, every 5 and 15 minutes, halves, and entire match. High-intensity accelerations (ACs) and a new index of performance efficiency (Effindex) were also examined during each match. The FR completed longer distances for all walking and running activities and exhibited a greater match HR compared with the AR. The FR exhibited a significant reduction in the mean number of ACs during the second half (40 vs. 28), with a significantly worse Effindex at the end of both halves for FR and at the end of the second half for AR. A significant correlation between FR and AR for the number (r = 0.336; p = 0.03) and distance (r = 0.367; p = 0.017) of ACs performed each 5-minute period indicated a synchronization of officials' activities. In conclusion, top-class American FR and AR exhibited similar physical demands as previously reported by their European counterparts during international tournaments. The high number of AC observed, the effect of fatigue on these actions over the match, and the AC's synchronization between FR and AR suggest that ACs should be considered for the preparation of referees and team sport athletes. The Effindex may provide an important tool for the evaluation of referees' and players' performance that requires further investigation.