Sex-Specific Associations Between Pubertal Stage and Objectively Measured Physical Activity in Early Adolescence: Evidence from the ABCD Study
Using data from 4,794 adolescents in the ABCD Study, this research reveals that while physical activity generally declines and sedentary time increases with advancing puberty, these changes occur earlier in males than in females, highlighting mid-to-late puberty as a critical window for sex-specific interventions to preserve daily movement.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Adolescence is a time of profound transformation, not just for the mind but for the body. As children grow into teenagers, they navigate a biological shift known as puberty, a period marked by hormonal surges and the emergence of secondary sexual characteristics. This transition is rarely uniform; it happens at different speeds and times for different people, creating a complex landscape of development. Alongside these physical changes, a well-documented trend occurs: young people tend to move less. They spend more time sitting and fewer hours engaging in active play or exercise. This decline in movement is a significant public health concern because physical activity is a cornerstone of long-term health, protecting against conditions like obesity and type 2 diabetes while supporting mental well-being. While it is known that girls generally move less than boys during these years, the precise moment when these differences sharpen, and how the stages of puberty specifically influence daily movement, have remained somewhat unclear. Understanding these patterns is essential for creating effective ways to keep teenagers active.
A recent study published in the journal Scientific Reports sought to illuminate these hidden patterns by looking at a massive group of American teenagers. Researchers analyzed data from the Adolescent Brain Cognitive Development Study, a large-scale project tracking thousands of children. For this specific investigation, the team focused on 4,794 adolescents, roughly half of whom were girls, with a median age of 12 years. Instead of relying on memory or self-reports, which can be unreliable, the researchers used a more precise method: they examined 21 days of continuous data recorded by Fitbit devices worn by the participants. These trackers provided an objective, minute-by-minute account of how much the teens moved, how long they sat, and how many steps they took each day. The researchers then grouped the participants by their stage of puberty, ranging from pre-puberty to late puberty, to see how their activity levels changed as they matured.
The results painted a clear picture of a general decline in movement as puberty advanced, but the timing of this decline differed significantly between boys and girls. Overall, the study confirmed that girls were less active than boys. On average, the girls in the study took about 8,754 steps per day and engaged in roughly 22 minutes of moderate-to-vigorous physical activity, which is the kind of energetic movement that gets the heart rate up. In contrast, the boys took about 10,431 steps per day and accumulated nearly 49 minutes of that higher-intensity activity. Despite these differences in movement, the amount of time spent sitting was similar for both sexes. However, as the teenagers moved through the stages of puberty, a distinct shift occurred. For both boys and girls, the time spent sitting increased, and the number of steps taken decreased.
The critical finding of the study lies in when these changes became statistically significant for each sex. For boys, the shift began earlier. As they moved from early puberty into mid-puberty, their sedentary time started to rise noticeably, and their daily step counts began to drop. By the time they reached late puberty, these trends were well-established. For girls, the pattern was delayed. While they were already less active than boys, their significant increase in sitting time and drop in steps did not become statistically apparent until they reached late puberty. This suggests that the biological and social pressures of puberty affect boys and girls on different timelines. Furthermore, the study found that moderate-to-vigorous physical activity did not show a consistent link to pubertal stage once other factors like age and body mass were accounted for. This implies that the decline in overall movement is driven more by an increase in sitting and a reduction in general walking rather than a specific drop in high-intensity exercise alone.
Perhaps the most striking observation was that no group of teenagers, regardless of sex or pubertal stage, met the World Health Organization's recommendation of 60 minutes of moderate-to-vigorous physical activity per day. Every single group fell short of this target. The researchers noted that while the overall direction of change was the same for everyone—moving less and sitting more as they grew older—the window for intervention appears to be different. For boys, the mid-puberty period seems to be the critical moment when habits begin to shift toward inactivity. For girls, the most pronounced changes occur later, during late puberty. This distinction suggests that a one-size-fits-all approach to encouraging physical activity may not work. Instead, strategies to reduce sedentary time and preserve daily movement might need to be tailored to these specific developmental windows, addressing the unique biological and social challenges that boys and girls face at different points in their journey through adolescence.
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