This study examined whether students’ internal and external exercise loads during middle-school physical education (PE) differ by sex, grade, and class type (teaching content). Internal and external load data were collected during regular PE lessons from a nine-year compulsory public school in Beijing (March–July 2024). Load was measured using wearable devices, including heart-rate monitoring and motion/position sensing. Internal-load indicators were average heart rate (Avg HR) and training impulse (TRIMP), and external-load indicators were covered distance and maximal speed. To account for the clustered and repeated-measures structure of the data, outcomes were analysed using linear mixed-effects models with sex, grade, and class type as fixed effects, and a random intercept for student (sex × class type interaction included). Statistical significance was set at p 125 bpm; mean TRIMP > 110 AU). Boys exhibited higher internal and external loads than girls across all outcomes. Load also differed by grade: Grade 8 tended to show higher internal load than other grades; Grade 7 demonstrated higher maximal speed than Grades 8–9; and Grade 9 accumulated greater covered distance than Grades 7–8. Class type showed clear differences in both internal and external load, with ball-game classes (e.g., soccer) generally producing higher Avg HR, TRIMP, distance, and maximal speed than athletics/track-and-field, gymnastics, and martial arts. Exercise load during PE varies meaningfully by gender, grade, and class type. Ball-game classes—particularly soccer-oriented lessons—tended to elicit the highest combined internal and external load stimuli. Integrating wearable monitoring into routine PE may support differentiated instruction and evidence-based lesson design by providing objective load metrics.
Gong et al. (Wed,) studied this question.