Daily exercise improves adolescent mental health — but too much may backfire

A large-scale study published in Psychiatry Research suggests that physical activity is associated with better mental health outcomes in adolescents, but only up to a point. Using wearable devices and brain imaging data, researchers found that moderate amounts of activity — but not excessive exercise — were linked to fewer internalizing and thought problems. The findings also revealed brain connectivity patterns and genetic markers that may help explain how physical activity supports mental well-being during this critical stage of development.

Adolescence is a time of major brain growth and emotional change. Many mental health conditions, such as anxiety and depression, first appear during this period. While there is strong evidence that physical activity benefits adult mental health, it’s less clear how much exercise is ideal for young people or what brain mechanisms are involved. The new study aimed to address those questions by identifying how different types and amounts of activity relate to mental health in early adolescence, and by exploring the brain and genetic pathways that might underlie those connections.

“Adolescent mental health problems are a significant public health concern worldwide. Although physical activity and exercise have been associated with better mental health in adults, the evidence in children and adolescents is mixed,” said study authors Jie Zhang, a professor at Fudan University, and Gechang Yu, a PhD student at the Chinese University of Hong Kong.

“Answering the question, ‘What are the optimal type, frequency, and duration of physical activity for adolescent mental health?’ is an important step toward developing personalized, activity-based prescriptions. Wearable devices can provide more accurate information than self-reported questionnaires. More importantly, the genetic and neural pathways through which physical activity influences mental health in adolescents remain unclear. Understanding these mechanisms can help develop targeted interventions for youth mental health problems.”

The researchers used data from the Adolescent Brain Cognitive Development (ABCD) study, a long-term project following thousands of children across the United States. The sample for the current analysis included 7,188 participants who were around 11 to 12 years old. Each participant wore a Fitbit wrist device for three weeks to measure daily steps and time spent in different levels of activity: light, moderate, and vigorous. The team also collected self-reported and parent-reported data on exercise habits and sports participation.

Mental health was assessed using the Child Behavior Checklist, a tool completed by parents that measures internalizing problems (such as anxiety or sadness), externalizing problems (such as aggression), and thought problems (such as unusual thinking or poor attention). In addition to behavioral data, the study included genetic information and brain scans to explore how physical activity might influence mental health through biological pathways.

The findings showed that adolescents who were more physically active tended to have fewer internalizing and thought problems. This was true across all activity levels, from light walking to vigorous exercise. However, there was no strong link between physical activity and externalizing problems. Interestingly, the relationship between exercise and mental health was not linear. Instead, moderate durations of activity were associated with the best outcomes.

Specifically, about 90 minutes of moderate activity or 120 minutes of vigorous activity per day was linked to the lowest mental health burden. Adolescents who reported exercising four days a week showed similar benefits. Exceeding these amounts — such as exercising vigorously for more than two hours per day — was not associated with additional improvements and in some cases was linked to worse mental health outcomes. This pattern, sometimes described as a “U-shaped” curve, suggests that more exercise is not always better.

The findings indicate that “doing physical exercise for about three to four times a week and 90 minutes each time is optimal for adolescent mental health,” Zhang and Yu told PsyPost.

The study also examined how these relationships varied by sex. Light activity was more strongly associated with improved mental health in girls, while boys benefited more from vigorous exercise. However, light activity was also linked to more externalizing problems in boys. These differences highlight the need for tailored recommendations that take into account both activity type and individual characteristics.

To explore potential biological explanations, the researchers looked at genetic risk scores for several psychiatric disorders, including anxiety, depression, attention-deficit/hyperactivity disorder, and schizophrenia. They also included genetic scores related to physical activity. The results showed that genetic risk for mental illness was linked to lower activity levels, especially light activity and walking. Conversely, having a genetic tendency to walk more was linked to fewer thought problems. These findings suggest that genetic factors influence both how active a young person is and how vulnerable they are to mental health difficulties.

“Adolescents’ inactivity is influenced by genes associated with neuropsychiatric disorders,” the researchers said.

Brain scans provided additional insight. The team found that higher levels of physical activity were associated with changes in the way different brain regions communicate with each other. Specifically, better mental health was linked to stronger connectivity between brain networks involved in sensory and motor processing and weaker connectivity between networks involved in cognitive control and auditory processing. These patterns were found across multiple types of activity and appeared to mediate the relationship between physical activity and mental health.

Interestingly, the researchers found that brain structure — such as the size or thickness of certain brain regions — was not as strongly related to physical activity or mental health. Instead, patterns of functional connectivity, or how different brain networks communicate during rest, played a more central role.

“We found that the effects of physical activity on mental health act more through brain function than through brain morphology in adolescence,” Zhang and Yu said.

These results suggest that exercise may influence adolescent mental health by shaping the way the brain processes information and coordinates between regions responsible for attention, motor skills, and emotional regulation. They also imply that moderate levels of physical activity may support optimal brain function during this developmental window, while too much activity may disrupt these processes.

The study had several limitations. It was based on cross-sectional data, meaning that it captured a snapshot in time rather than tracking changes over time. As a result, it cannot prove that physical activity causes better mental health — it could be that adolescents with better mental health are simply more active. Also, the study relied on observational data, and although it adjusted for many factors, unmeasured variables could still play a role.

“Experimental and intervention studies are needed to further confirm the causality between physical activity, mental health and brain function,” Zhang and Yu said.

Despite these limitations, the study offers one of the most comprehensive looks to date at how physical activity relates to mental health in early adolescence. By combining wearable device data, brain imaging, and genetics, it provides a clearer picture of the biological pathways involved and highlights the importance of finding a balance in exercise routines.

“We hope to validate current findings in other cohorts and populations, and assess if the identified associations are consistent during the whole period of adolescence,” Zhang and Yu said.

The study, “Genetic Influence and Neural Pathways Underlying the Dose-Response Relationships Between Wearable-Measured Physical Activity and Mental Health in Adolescence,” was authored by Gechang Yu, Xinran Wu, Zhaowen Liu, Mai Shi, Huaxin Fan, Yu Liu, Nanyu Kuang, Songjun Peng, Zhengxu Lian, Chuiguo Huang, Hongjiang Wu, Baoqi Fan, Jianfeng Feng, Wei Cheng, Barbara J. Sahakian, Trevor W. Robbins, Benjamin Becker, and Jie Zhang.