Objective  This study explores the gender, grade, and characteristics of exercise load in middle school physical education (PE) classrooms through non-interference intelligent monitoring, and examines the internal relationship of factors affecting the standard-reaching rate of classroom exercise load.

Methods A stratified cluster sampling method was adopted, with four classes of students (89 males and 67 females) in the first and second grades of a middle school in Ningbo city as well as 118 PE and health classes as the research objects. Relevant factors on the standard-reaching rate of students' exercise load were collected and analyzed using questionnaire surveys, testing methods, and other methods.

Results  ① The exercise load standard-reaching rate are better in grand PE classes than in basketball classes, and are better than in track and field classes. ② There is a significant difference in the exercise load in genders (t=1.682, P<0.05) and grades (t=−3.335, P<0.01), with boys higher than girls and the eighth grade higher than the seventh grade. ③ The threshold for achieving 80% (OR_80%=3.02, P<0.05) and 85% of exercise load (OR_85%=4.33, P<0.05) is significantly lower for girls than for boys. At the threshold of 75% exercise load achievement rate, the probability of achieving the goal in eighth grade is significantly higher than that in seventh grade (OR=6.91, P<0.05).

Conclusions ① There is a significant difference in standard-reaching rate of exercise load in different PE courses, genders and grades. ② There is no difference in standard-reaching rate of exercise load among different physical fitness and weight levels; ③ The target rate of exercise load reaches the level range of 80% or above, and the probability of male students achieving the target rate higher than female students.