Monitoring Training in Elite Soccer Players: Systematic Bias between Running Speed and Metabolic Power Data

We compared measurements of high-intensity activity during field-based training sessions in elite soccer players of different playing positions. Agreement was appraised between measurements of running speed alone and predicted metabolic power derived from a combination of running speed and acceleration. Data was collected during a 10-week phase of the competitive season from 26 English Premier League outfield players using global positioning system technology. High-intensity activity was estimated using the total distance covered at speeds >14.4kmh(-1) (TS) and the equivalent metabolic power threshold of >20Wkg(-1) (TP), respectively. We selected 0.2 as the minimally important standardised difference between methods. Mean training session TS was 478 +/- 300m vs. 727 +/- 338m for TP (p<0.001). This difference was greater for central defenders (similar to 85%) vs. wide defenders and attackers (similar to 60%) (p<0.05). The difference between methods also decreased as the proportion of high-intensity distance within a training session increased (R-2=0.43; p<0.001). We conclude that the high-intensity demands of soccer training are underestimated by traditional measurements of running speed alone, especially in training sessions or playing positions associated with less high-intensity activity. Estimations of metabolic power better inform the coach as to the true demands of a training session.