External Load During Warm-Up and Early-Match Running Performance of Starting and Substitute Football Players: A Within-Player Comparison

Objectives: This study aimed to: (1) compare the absolute and relative external load during the warm-up of starting and substitute professional football players; (2) describe the subsequent running performance during the first 15 min of match play; and (3) quantify the within-player variability of the warm-up (WU) external load between roles. Methods: Sixteen professional male players (Swiss Second Division) were monitored using 10 Hz GPS units across 13 official matches (106 observations). Starters completed a standardized ~25 min on-field warm-up, while substitutes performed a cyclical sideline warm-up. Running performance was analysed during the first 15 min of play and across three consecutive 5 min intervals (0–5, 5–10, and 10–15 min) in the same players under both match-entry conditions: starters and substitutes. Results: Starters’ warm-up showed significantly longer duration (p < 0.001; d = 3.5), greater total distance covered in both absolute and relative terms (p < 0.001, d = 6.6; p < 0.001, d = 5.1, respectively), and higher maximal speed (p < 0.001; d = 1.4) compared to substitutes. However, substitutes covered more distance between 19.8 and 25.2 km·h−1 in either absolute and relative terms (p < 0.05, d = 1.3; p < 0.001, d = 3.6; respectively). No significant differences were found in external load during the overall 0–15 min match period between roles. Nevertheless, block-specific analysis revealed that substitutes performed significantly a greater number of decelerations (p < 0.05; d = 0.5), distance covered between 19.8 and 25.2 km·h−1 (p < 0.05; d = 0.79) and sprinting during the initial 0–5 min period (p < 0.05; d = 1.24). Conclusions: Substitutes’ warm-up exhibited substantially higher variability across almost all external load metrics compared with the warm-up completed by the starters, except for slightly higher or identical variability in the number of accelerations and decelerations.