In recent years, the excessive use of electronic products and the continuous increase of academic pressure have made sedentary behavior become the normal performance of young people’s study and life. Yang Jian et al. (1) found that 86.67 and 63.67% of middle school students in Henan had more than 8 h of sedentary time on school days and rest days, respectively. According to Wang Fubaihui et al. (2), the sedentary time of Chinese teenagers on school days is about 6.5 h, and the sedentary time on rest days is more than 10 h. The Global Physical Activity Report for Children and Adolescents shows that (3) nearly 80% of Chinese children and adolescents exceed the recommended amount of sedentary time. Epidemiological studies have found that sedentary behavior is closely related to lower VO₂ Max, muscle strength and flexibility levels in adolescents. At the same time, relevant reports have shown that sedentary behavior has a significant dose relationship with cardiovascular diseases such as adolescent obesity (4), hypertension (5), inflammation (6, 7), metabolic syndrome and psychological diseases such as depression. The occurrence of the above chronic diseases caused by long-term sitting may be related to metabolic changes, hemodynamic changes and inflammation. It is well known that sedentary behavior can significantly reduce muscle activity and reduce blood circulation rate, thus increasing the risk of thrombosis. Long-term sedentary behavior will further inhibit muscle metabolism of glucose, which may lead to insulin resistance and diabetes. In addition, long-term sitting will also lead to the increase of inflammatory markers and oxidative stress, all of which have been proved to be the key to the occurrence and development of chronic diseases. How to reduce the sedentary behavior of adolescents and offset the negative effects of sedentary behavior on health has become an urgent public health problem. Healy‘s (8) study revealed for the first time the positive effects of sedentary intermittent behavior on obesity, sugar and lipid metabolism in adults. In recent years, more and more studies have found that sedentary intermittent intervention has a significant impact on the health level of college students (9), office workers (10) and the older adults (11). However, there are few reports on the effects of intermittent sedentary intervention on middle school students.

Based on this, this study takes junior middle school students as the research object, and explores the impact of increasing fragmented physical exercise time on the health level of sedentary adolescents and children by carrying out physical exercise between classes, so as to provide empirical evidence for effectively avoiding the potential health risks brought by sedentary adolescents and children.

With the change of production and life style, the popularization of modern intelligent tools, the necessary physical activity of human beings continues to decrease, and sedentary life has become the norm of people’s work and life. Studies have shown that sedentary behavior in adolescents is one of the risk factors for physical diseases such as overweight, obesity, hypertension, cardiometabolic risk (17) and psychological disorders such as depression, anxiety (18) and suicide attempt (18). How to reduce the sedentary time of adolescents and alleviate or eliminate the negative impact of sedentary time on the physical and mental health of adolescents has become a worldwide public health problem that needs to be solved urgently. However, the close curriculum arrangement of the school day makes it difficult to reduce the sedentary time of adolescents, so it is more worthwhile to explore and study the potential risks brought by different ways to curb sedentary time.

This study found that recess physical exercise can significantly improve junior middle school students’ academic performance and mental health level, muscle mass and maximal oxygen uptake, delay the increase of blood pressure and the decrease of vision, reduce their body fat percentage, and improve their heart rate variability.

Gonzalez-Sicilia (19), PindusDM (20) and Isensee et al. (21) found in their studies that increasing physical exercise has a positive effect on improving students’ academic performance. Although the significant benefits of increased physical activity in improving academic performance have been widely recognized (22–24), these studies have focused more on the effects of after-school and longer periods of physical activity on academic performance, and relatively little research has been done on the relationship between recess physical activity and academic performance. However, limited studies have also shown that increasing pre-class exercise can significantly improve children’s cognitive function and thus positively influence academic performance (25).

While our results demonstrate a significant positive association between recess physical activity and academic performance, the underlying neurobiological mechanisms require further investigation. Potential pathways suggested by prior research include increased secretion of brain-derived neurotrophic factor (BDNF) (26, 27) and enhanced neurovascular adaptation with synaptic plasticity (28, 29), which may collectively improve cognitive functions—particularly attention and working memory—that support academic engagement (30). Critically, as BDNF levels and neurostructural changes were not quantified in the present study, these remain hypothetical pathways warranting verification through future biomarker-integrated trials employing serum assays and neuroimaging techniques.

In addition, studies have pointed out that there is a significant increase in sedentary time among adolescents from primary school to middle school, and epidemiological studies have shown that continuous sedentary time will increase the risk of overweight and obesity, cognitive function decline, and depressive symptoms in adolescents and children (31–34), which will adversely affect their academic performance. Increasing physical activity between classes significantly reduced the amount of time students spent sitting and improved their academic performance.

Continuous sedentary state will lead to the imbalance of energy consumption and intake of the body, and sedentary state will reduce the oxidation of lipids in muscle tissue, which will lead to continuous accumulation of lipids and eventually lead to overweight and obesity (35, 36). Animal experiments also found that the restriction of activity would lead to the disturbance of the secretion of lipocalin2 (LCN2), which is related to appetite regulation and energy metabolism, and osteocalcin (OCN), which is related to glucose uptake in skeletal muscle, resulting in food intake level and weight gain. On the one hand, the improvement of sedentary intermittent exercise on body composition comes from the increase in energy consumption during and after exercise, which causes the decomposition of body fat and inhibits the accumulation of fat cells. At the same time, exercise stimulates the secretion of leptin, insulin and other hormones and mediates the uptake of blood sugar and blood lipids by skeletal muscle, thus reducing the risk of obesity (37). As early as 2008, Healy et al. found that frequent intermittent sedentary behavior can significantly reduce adult triglycerides and postprandial blood sugar and other indicators (8). Myashia et al. pointed out that obese young people who accumulated 10 times of medium-high intensity intersong exercise for 30 min would have a 39% decrease in TG 7 h after meals the next day (38). Bhammar et al. showed that a 2-min interval of moderate to high intensity every 20 min significantly reduced average blood glucose and systolic blood pressure levels in sedentary obese men. All the above studies have shown that sedentary intermittent intervention can have a positive impact on human glucose and lipid metabolism. However, most of the previous studies focused on the older adults, adults and college students and other groups, and this study proves that sedentary intermittent exercise also has potential benefits in young people.

The effect of sedentary intermittent exercise on blood pressure and heart rate variability may be mainly due to the fact that continuous sedentary immobility will lead to the accumulation of lower limb veins, the decrease of arterial blood flow, velocity and shear stress, resulting in excessive release of endothelin 1 and the decrease of bioavailability of nitric oxide (itricoxide NO), which will eventually lead to the damage of vascular endothelial cells, relaxation and relaxation of blood vessels. Formation of hypertension and blood clots (39, 40). Intermittent exercise can enhance the pumping function of lower limbs, promote blood circulation, increase artery dilation, stimulate NO production and availability of endothelial cells, enhance endothelial cell function and improve blood pressure. Heart rate variability is one of the important biomarkers used to assess autonomic nervous system function (ANS), and many studies have shown that higher heart rate variability values, i.e., strong vagal response, are associated with positive health outcomes, while lower heart rate variability indicates inadequate adaptation of the autonomic nervous system and higher sympathetic nerve activity. This study found that sedentary intermittent intervention could significantly improve the heart rate variability of adolescents, and the overall level of HRV and vagal nerve activity in the experimental group were significantly better than those in the control group after intervention. Magnetic resonance imaging shows that prolonged sitting causes significant changes in the activities of the prefrontal cortex, insula and limbic system cortex, and inactivation of the ventromedial prefrontal cortex leads to overactivity of the amygdala, amplifies the perception of fear and pressure, and keeps people in a state of stress with sympathetic excitation and reduced parasympathetic output. In turn, the sympathetic nerve tension such as heart rate, blood pressure and HRV led to changes in cardiovascular activity.

The study found that with the increase of age, the eye diopter of children showed a downward trend. Although intermittent exercise intervention could not completely prevent the decline of children’s diopter, it could effectively slow down the decline rate and delay the occurrence of myopia in children. This is similar to the results of Guggenheim et al. (41). Studies have shown that the benefits of sports in the prevention and treatment of myopia are mainly attributed to the improvement of ocular muscle function and blood circulation during exercise, the decrease of intraocular pressure after exercise, the improvement of choroidal blood flow speed, and the adequate supply of retinal blood, and the higher level of retinal blood supply can effectively promote the development of ocular neuromuscles in children (42). In addition, the reason why this intervention can delay the diopter decline of the experimental subjects may be related to outdoor light. The prevention and treatment mechanism of light on myopia is mainly attributed to the “light-dopamine” hypothesis. Dopamine, as an important neurotransmitter, can effectively inhibit the increase of the length of the eye axis. It was observed in animal experiments that the rate of dopamine release from the retina of chicks increased log-linearly with the increase of light intensity (43). The exercise in this experiment was carried out outdoors, which may regulate the secretion of retinal dopamine by increasing outdoor light (44), and then affect the length of the axis of the eye, so as to prevent myopia.

This study demonstrates the efficacy of sedentary discontinuous interventions in improving cardiometabolic and psychosocial outcomes among adolescents, yet several limitations warrant attention. The single-center sample from Chongqing, China constrains geographical and cultural generalizability, necessitating future multi-center trials across diverse educational systems (e.g., Eastern vs. Western curricula) to verify transferability—particularly regarding curriculum-driven activity patterns and social acceptability of interventions. Furthermore, the lack of objective control group monitoring (e.g., accelerometry) impedes definitive causal attribution, we thus strongly endorse implementing wearable activity trackers for quantifying break-time behaviors and video-based behavioral coding for activity typology analysis. The limited sample size (N = 120) also precluded robust subgroup analyses, warranting larger cohorts (>500 participants) to investigate dose-response relationships by BMI percentile and moderating effects of socioeconomic status. To address these gaps, we propose a concrete research agenda: Phase 1 (2024–2025) conducts replication studies across three Chinese provinces, Phase 2 (2026–2027) implements cross-cultural RCTs comparing Confucian-heritage and Western schools, Phase 3 integrates interventions into national physical education frameworks for policy-effectiveness trials.

Through this study, we found that one academic year of recess physical exercise can significantly improve students’ academic performance, alleviate students’ learning burnout and depression, improve the quality of students’ peer relationships, and promote the establishment of students’ interpersonal relationships; In addition, studies have also shown that increasing the time of physical exercise between classes can reduce students’ body fat percentage, increase body muscle mass, delay vision loss and blood pressure increase, increase students’ VO2 Max, and improve their heart rate variability. The results of this experiment suggest that in the context of the continuous increase of students’ learning pressure and learning time, fragmented physical exercise between classes can also relieve students’ psychological pressure, improve students’ physical health level, and promote students’ healthy growth.