Return of match running performance following muscle strain injuries of varying severity in professional football.

To examine match running performance recovery trajectories following muscle strain injuries of varying severity in professional male football players upon RTP. Forty-nine outfield players from a professional football team were prospectively monitored over four consecutive seasons (n=168 non-contact lower-limb muscle strain injuries). Injuries were classified by severity (time loss) as mild (1-7 days), moderate (8-28 days), or severe (> 28 days). GPS-derived match metrics were analysed across the four matches preceding injury and across 14 matches following RTP (i.e., POST 1-to-14) to characterise the recovery trajectory. Generalised additive mixed models were fitted to describe nonlinear recovery patterns. Recovery trajectories differed significantly between severity groups (R2 95%IC = 0.360 to 0.425, p < 0.001). Mild injuries caused short impairments with reductions of -19 to -27% in match running metrics at POST1 (ES: 0.25 to 1.05) that persisted up to POST2; per-minute intensities remained largely preserved. Moderate injuries caused large impairments, in sprinting, high-speed running, and accelerating/braking actions (-62% to -92% at POST1), and remained below baseline at POST3 (ES: 0.24 to 3.12); per-minute metrics revealed some residual neuromechanical deficits beyond minutes restriction. Severe injuries caused similar pronounced acute impairments (-60 to -100% at POST1) but the longest persistent deficits up to POST4 in absolute metrics and up to POST7 for high-speed running (ES: 0.28 to 2.31). Match running performance in the RTP after muscle strain injury follows a clear severity-dependent recovery: mild injuries recovered within two matches, moderate in three, severe injuries after four or more, particularly in high-speed and accelerating/braking actions.