Effects of acute warm-up intensity and baseline fitness on running performance in adolescents.

This study investigated the interactive effects of acute warm-up intensity and baseline physical fitness on cardiovascular responses and subsequent running performance in adolescents within a school-based physical education setting. In a counterbalanced, repeated-measures crossover design, 132 adolescents completed a low-intensity warm-up (self-paced walking) and a moderate-intensity warm-up (modified interval-based circuit, ~70% estimated HRmax) on separate occasions, each followed by a 20-minute self-paced running task. After quality control, valid running performance data were obtained from 110 participants, and heart rate data were analyzed in a stratified subsample of 100 participants. Baseline fitness was categorized into middle-to-high fitness (grades 1-3) and low fitness (grades 4-5) based on national normative data from the Physical Activity Promotion System. Cardiovascular response, assessed as mean heart rate during the warm-up, and running performance outcomes, including total distance and mean speed, were analyzed using a mixed-effects model. A significant interaction between warm-up intensity and baseline fitness was observed for both total running distance (p = 0.027) and mean running speed (p = 0.030). Following the moderate-intensity warm-up, the middle-to-high fitness group demonstrated greater running distance and speed compared with the low-intensity condition, whereas the same standardized moderate-intensity warm-up did not improve performance in the low-fitness group. The moderate-intensity warm-up elicited higher mean heart rate than the low-intensity warm-up across participants (p < 0.0001), with no significant interaction between warm-up intensity and fitness level. These findings suggest that baseline fitness may moderate the performance response to an acute warm-up in adolescents. Overall, a universal warm-up prescription may not be equally effective across students with varying fitness levels, and individualized, relative-intensity approaches warrant further investigation in school-based physical education settings.