Measuring Physical Load in Soccer: Strengths and Limitations of 3 Different Methods

To investigate the strengths and limitations of different indicators to measure physical load. Furthermore, indicators were evaluated for discrimination between performance levels and playing positions. Ninety positional match files from 70 elite players and 91 match files from 69 subelite players were collected during 14 official under-18 matches using a local position measurement system. Indicators are calculated from speed, absolute acceleration (acc-abs), or percentage acceleration (acc-%). The acc-% describes the level of acceleration depending on the maximal voluntary acceleration (a_max) for each initial running speed. Effect sizes (ES) were used to determine discriminative ability. The number of high accelerations largely depended on the method (absolute threshold [>3 m·s^-2 and >4 m·s^-2] 120 and 59 efforts; high percentage threshold [>75% a_max] 84 efforts). Only a small number of highly accelerated efforts reached speeds considered high-speed running (>19.8 km·h^-1: 32.6%). More high acc-% exists from initial running speed >2 m·s^-1 (23.0) compared with acc-abs (>3 m·s^-2 14.4, >4 m·s^-2 5.9). Elite players achieve higher values in most performance indicators, with ES being highest for the number of high acc-% (ES = 0.91) and high acc-abs (>3 m·s^-2 ES = 0.86, >4 m·s^-2 ES = 0.87), as well as for covered distance in jogging (ES = 0.94). Estimated physical load, discriminative ability of physical indicators, and positional requirements largely depend on the applied method. A combination of speed-based and acc-% methods is recommended to get a comprehensive view.