MONTORING TRAINING IN ELITE SOCCER: A NEW APPROACH BASED ON GPS DERVIED ESTIMATED METABOLIC POWER DATA

Introduction: Several studies have previously analysed soccer training sessions and specific drills However, a new method was recently proposed to estimate energy cost and metabolic power from acceleration data together with the evolution of global positioning system (GPS), providing the opportunity to derive a more detailed and accurate description of the physical demands imposed to the player during training. Purpose: The aims of the present investigation were to: i) compare measurements of high-intensity activity when calculated as high running speed or high predicted metabolic power derived from a combination of running speed and acceleration during field-based soccer training sessions; ii) evaluate the agreement between the two methods during soccer small-sided games (SSGs); iii) evaluate whether any bias between the two approaches is dependent upon playing position; iv) examine the extent to which changing the game format (possession play (SSG-P) vs game with regular goals and goalkeepers (SSG-G)) and the number of players (5vs5, 7vs7 and 10vs10) influenced the physiological and physical demands of SSGs. Methods: Data were collected in training during the in-season period from 26 English Premier League and UEFA Champions League outfield players using global positioning system technology. Total distance covered, distance at different speed categories and maximal speed were calculated. In addition, the number of changes in velocity carried out and the absolute maximal values of acceleration and deceleration achieved were reported. By taking into account these parameters besides speed and distance values, estimated energy expenditure and metabolic power were calculated. Finally, high-intensity activity was estimated using the total distance covered at speeds >14.4 kmh-1 (TS) and the equivalent metabolic power threshold of >20 Wkg-1 (TP). Results: Mean training session TS was 478 ± 300 m vs 727 ± 338 m for TP (p<0.001). This difference was greater for central defenders (85%) vs wide defenders and attackers (60%) (p<0.05). The difference between methods also decreased as the proportion of high-intensity distance within a training session increased (R2=0.43; p<0.001). When different SSGs were analysed, high-intensity demands were systematically higher (~100%, p<0.001) when expressed as TP vs TS irrespective of playing position and SSG. The magnitude of this difference increased as the size of SSG reduced with a difference of ~200% observed in the 5vs5 SSG (p<0.01). A greater difference between TP and TS was also evident in central defenders compared to other positions particularly during the 5vs5 SSG (~350%; p<0.05). In addition, the total distance, distances run at high speed (>14.4 km•h-1) as well as maximum velocity, acceleration and deceleration increased as pitch dimensions increased (10v10>7v7>5v5; p<0.05). Furthermore, the total distance, very high (19.8-25.2 km•h-1) and maximal (>25.2 km•h-1) speed distances, absolute velocity and maximum acceleration and deceleration were higher in SSG-G than in SSG-P (p<0.001). On the other hand, the number of moderate acceleration and decelerations as well as the total number of changes in velocity were greater as the pitch dimensions decreased (i.e. 5v5>7v7>10v10; p<0.001) in both SSG-G and SSG-P. Finally, predicted energy cost and metabolic power were higher in SSG-P compared to SSG-G and in larger compared to smaller pitch areas (p<0.05). Conclusions: The high-intensity demands of soccer training are underestimated by traditional measurements of running speed alone, especially in central defenders, training sessions associated with less high-intensity activity and “small” SSGs. Estimations of metabolic power better inform the coach as to the true demands of a training session or a particular drill. A detailed analysis of different drills based on metabolic power is pivotal in contemporary football as it enables an in depth understanding of the workload imposed on each player which consequently has practical implications for the prescription of the adequate type and amount of stimulus required during training.