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The aims of this study were to establish sources of variability in match physical performance of professional soccer players and provide a method for monitoring individual between-match changes. Eleven players meeting the final inclusion criteria were monitored through an entire in-season competition phase (n = 240 individual match observations). Ten Hertz global positioning systems were used to measure match total distance (TD), total high-speed running distance (≥ 21 km·h−1; HSRD), total accelerations (TAcc) and maximum running velocity (Vmax). Between-player, between-position, between-match and within-player variability were determined through linear mixed effects models. These data were then used to establish the practical significance of individual changes using a Minimum Effects Testing framework. All sources of variability were greater for HSRD (13–36%) when compared with all other metrics (<6%). Using combined between-match and within-player variability along with the smallest worthwhile change (0.2 × between-player SD), between-match individual changes of ±∼10–15% in TD, TAcc and Vmax were established as practically significant. For HSRD, these thresholds were considerably higher (≥60%). In conclusion, the ability for soccer practitioners to identify meaningful changes in match physical performance can aid decision making around player management following competition. Our study provides a method to flag changes beyond the normal match-to-match variability and by a substantial magnitude. This may have implications for recovery but should be combined with other sources of data (internal load and response) and used only as an adjunct to practitioner domain knowledge/experience. [ABSTRACT FROM AUTHOR]

In order to better understand the intensity of match activities of full-match and substitution football players, running performance of 527 players who generated 1167 match observations in the 2018 FIFA World Cup were analysed. Differences in activity profiles between groups (1st and 2nd half full-match, early and late substitutes) were quantified by the generalised mixed linear modelling. Results showed that: (1) Full-match players presented trivial changes (ES: 0.09–0.20) in the time spent (% of total playing time) and distance (m/min) covered at high intensity but substantial descents (ES: 0.33–0.61) at moderate and low intensity from the 1st to the 2nd half. (2) Early substitutes achieved substantially higher (ES: 0.27–0.65) numbers in time spent and distance covered at high and moderate intensity, but lower (ES: 0.27–0.46) numbers in walking and jogging time and distance than 1st and 2nd half full-match players. (3) Late substitutes achieved substantially higher (ES: 0.28–1.26) numbers in time spent and distance covered at high and moderate intensity but substantially lower (ES: 0.39–1.06) numbers in top speed (km/h), walking and jogging time and distance than 1st and 2nd half full-match players and early substitutes. Results of this study could provide insights to the design of post-match conditioning sessions. [ABSTRACT FROM AUTHOR]