Children and adolescents with higher aerobic fitness tend to have a lower risk of developing clinical depression by middle age, according to new research published in Journal of Affective Disorders. Tracking more than 1,000 Australians over more than three decades, the study indicates that faster running speeds and better endurance in youth are linked to a lower risk of developing depression in adulthood, particularly among women. In contrast, childhood muscular power and strength showed much weaker and less consistent ties to adult mental health.
Depression is a mood disorder characterized by persistent sadness, loss of interest in everyday activities, and feelings of worthlessness that impair daily functioning. Because antidepressant medications often carry unpleasant side effects and do not work for everyone, scientists have sought to identify modifiable factors that might help prevent depression across the lifespan. Much of this work has focused on physical activity, which refers to any bodily movement that burns energy, such as walking or playing sports. Physical fitness, by contrast, is an objective measure of how well the body’s heart, lungs, muscles, and metabolic systems have adapted to perform physical work.
Fitness is broadly divided into cardiorespiratory fitness, which is the ability of the circulatory and respiratory systems to supply oxygen to muscles during sustained exercise, and muscular fitness, which includes brute strength and explosive power. Among adults, higher fitness has been linked to better mental health; for example, a prospective cohort study of British adults found that individuals with the lowest aerobic and muscular fitness had nearly double the odds of developing depression seven years later compared to those with high fitness.
Extending this view to late adolescence, a 2012 population-based study of over one million 18-year-old Swedish male military conscripts indicated that young men with low or medium aerobic fitness and muscle strength faced an elevated risk of serious depression up to four decades later.
Whether those long-term protective patterns hold true for girls, or for fitness measured earlier in childhood, has remained unknown. In younger populations, a 2021 meta-analysis of cross-sectional studies in children and adolescents found that youths with better aerobic endurance tended to report fewer depressive symptoms at the time of testing, and a 2015 longitudinal study of middle school students indicated that sixth-graders with higher aerobic fitness were less likely to develop depression by seventh grade.
However, no study had objectively measured fitness in childhood and then tracked depression into adulthood. To address this question, Kylie J. Smith and Brooklyn J. Fraser of the Menzies Institute for Medical Research at the University of Tasmania, along with their colleagues, examined whether childhood endurance and muscle performance predicted clinical depression decades later.
“Depression is a major public health challenge, and there is growing interest in identifying factors earlier in life that may contribute to better long-term mental health,” said Fraser, a postdoctoral research fellow at the Menzies Institute for Medical Research at the University of Tasmania who is also affiliated with Adelaide University. “We know that being physically active is good for mental health, and previous research has shown that fitter adults are less likely to develop depression. However, much less is known about whether fitness during childhood and adolescence is related to depression decades later. Using more than 30 years of follow-up data from the Childhood Determinants of Adult Health (CDAH) Study, we had a rare opportunity to explore that question.”
The researchers analyzed data beginning with the 1985 Australian Schools Health and Fitness Survey, which tested a nationally representative sample of 8,498 schoolchildren aged 7 to 15 years. A subset of these participants was traced into adulthood and attended follow-up clinics between 2014 and 2019, when they were 36 to 49 years old. The final analysis included up to 1,080 adults, comprising 519 men and 561 women, who had completed childhood fitness testing, provided background data, and finished a mental health diagnostic interview after an average follow-up of 32.5 years.
“One of the major strengths of this study is the long follow-up period,” Fraser told PsyPost. “Few studies have objectively measured fitness in childhood and then assessed depression more than 30 years later. This long-term study by the Menzies Institute for Medical Research has helped to better inform us about how health in childhood may influence well-being and other health outcomes across adulthood.”
During the 1985 survey, children aged 7 to 15 completed a timed 1.6-kilometer (one-mile) run or walk on a flat course to measure cardiorespiratory fitness, which was converted into average running speed in meters per minute for 1,062 participants in the final sample. Due to time and resource limits in 1985, a smaller subset of children aged 9, 12, and 15 years, totaling 437 participants in the final analysis, also completed a submaximal stationary bike test, an assessment that does not require an all-out effort.
Youths pedaled across three three-minute stages of increasing resistance while assessors measured their heart rate with a stethoscope and stopwatch to estimate their physical work capacity at 170 beats per minute, meaning the workload a child could sustain at that heart rate. Because muscle mass affects pedaling power, the researchers statistically removed the influence of lean body mass, estimated from skinfold measurements, from the cycling scores.
The 1985 survey also assessed muscular power, which is the ability to exert force quickly, and muscular strength, the maximum force a muscle can generate in a single effort. All children aged 7 to 15 completed a standing long jump to measure muscular power, leaping forward from a two-footed standing stance using an arm swing, with the furthest of two jumps recorded. The subset of 9-, 12-, and 15-year-olds also completed a handgrip strength test using an adjustable mechanical grip device, squeezing with maximum force once with each hand. The researchers averaged the left and right hand scores, statistically removed the effect of total body weight, and standardized all four fitness measures for age and sex.
At the mid-adulthood clinics, participants completed a computerized version of the World Health Organization Composite International Diagnostic Interview. This standardized assessment identified lifetime major depressive disorder and dysthymic disorder, a chronic form of milder depression, using fourth-edition Diagnostic and Statistical Manual of Mental Disorders criteria, and recorded the age when symptoms first appeared.
Participants whose depression began in or before 1985 were excluded. The models controlled for childhood age, sex, body mass index (BMI), neighborhood socioeconomic status based on 1981 census postal codes, and another fitness measure from the same testing group, while applying statistical weights to account for participant dropout over the follow-up period.
Over the follow-up period, 190 of the 1,080 participants (17.6 percent) experienced depression, including 117 women (20.9 percent) and 73 men (14.1 percent). In survival analyses tracking the rate at which depression emerged over the entire follow-up window, the researchers examined a step up in childhood 1.6-kilometer running speed of one standard deviation, roughly the gap between an average child and one fitter than about five in six peers of the same age and sex. That step was associated with a 15 percent lower rate of developing depression when adjusting for age and sex.
After adding controls for standing long jump performance, neighborhood socioeconomic status, and childhood BMI, the size of that reduction remained unchanged at 15 percent, though the estimate was no longer statistically significant.
When the researchers examined men and women separately, the link between childhood aerobic fitness and adult depression appeared somewhat stronger in females than in males, though the researchers did not formally test this difference.
Among women, a one-standard-deviation increase in childhood running speed was associated with a 19 percent lower rate of depression, and a one-standard-deviation increase in stationary bike fitness was tied to a 28 percent lower rate in age-adjusted models. After full adjustment, these estimates were similar in size but no longer statistically significant.
Among men, childhood running speed and bike fitness were associated with 10 percent and 6 percent reductions in depression rates, respectively, neither of which was statistically significant, and neither standing long jump distance nor handgrip strength showed a statistically significant relationship with overall depression rates in either sex.
“We were interested to see that the association appeared stronger among females,” Fraser said. “However, our study was not designed to determine why this occurred, and further research is needed to better understand these differences.”
To evaluate how these associations changed over time, the team also calculated the cumulative risk of developing depression in five-year intervals after 1985, though the authors treat the survival analysis as their primary estimate and the early-interval figures rest on few cases. In fully adjusted models, higher running speed was linked to a 39 percent lower risk of depression onset within the first 5 years, when 2.5 percent of participants had developed depression, and a 25 percent lower risk within 10 years, when the base rate reached 5.2 percent.
Across the entire follow-up span, where 17.7 percent of the running sample and 17.2 percent of the cycling sample experienced depression, each standard-deviation increase in childhood running speed and bike fitness was associated with a 12 percent and 13 percent lower cumulative risk of depression, respectively.
In those interval analyses, standing long jump power showed no consistent tie to depression, while handgrip strength displayed a shifting pattern. Higher childhood grip strength was linked to a slightly higher or neutral risk of depression during the first 15 years of follow-up, before reversing into a modest protective association at 20 years (a 14 percent lower risk in fully adjusted models) and a borderline 5 percent lower risk across the full follow-up period. In sensitivity analyses that additionally accounted for childhood self-reported exercise levels and baseline feelings of unhappiness, the primary findings remained virtually unchanged.
“Higher cardiorespiratory fitness in childhood and adolescence was associated with a lower risk of depression in adulthood. This pattern was clearest for fitness measured by 1.6-km run speed,” Mohsen Joshanloo, a professor of psychology at Keimyung University in South Korea who was not involved in the study, told PsyPost.
“The key message is that the benefits of childhood fitness may extend beyond physical health,” Fraser explained. “Children and adolescents with better cardiorespiratory fitness were less likely to experience depression later in life. While fitness is unlikely to be the only factor influencing depression risk, it may be one important piece of the puzzle. Adequate fitness in childhood has both immediate and long-term benefits for cardiovascular health, and now we have found that fitness may also reduce the risk of depression in adulthood.”
The finding that childhood endurance predicts lower depression risk decades later aligns with an earlier review of prospective studies in adults, which found that low and medium cardiorespiratory fitness were linked to a 75 percent and 23 percent higher risk of depression compared to high fitness, even though that review examined adults rather than tracking fitness from youth. The results also parallel a meta-analysis evaluating cardiorespiratory fitness in middle-aged adults, which similarly linked each small step up in aerobic fitness to lower risks of depression, dementia, and psychotic disorders despite focusing on midlife rather than childhood fitness.
“The finding is consistent with prior research linking higher cardiorespiratory fitness to lower depression risk,” Joshanloo said. “It extends previous work by showing that this association can still be observed more than 30 years after fitness was measured in childhood and adolescence.”
“I believe that the study was conducted carefully and that the researchers used statistical methods that were well suited to their research question,” he added. “The evidence provides reasonably convincing support for an association between higher childhood cardiorespiratory fitness and a lower risk of depression in adulthood. However, the association was modest in size, and some of the findings were not conclusive. I would also be cautious about drawing causal conclusions.”
At the same time, the weak results for early muscular fitness stand in tension with some studies in older cohorts. For instance, a study examining genetically predicted fitness in middle-aged and older adults found that muscle strength, particularly in women, was associated with lower depression odds while aerobic fitness showed no association, though that work relied on genetic proxies in older adults rather than directly measured childhood fitness tracked over decades.
Similarly, a meta-analysis of handgrip strength in older adults reported that the weakest participants had a 26 percent to 42 percent higher risk of later-life depression than the strongest individuals, though that analysis evaluated grip strength in older age rather than tracking muscular fitness from childhood into mid-adulthood.
“Our findings identified cardiorespiratory fitness as a potentially important factor that may contribute to long-term mental health,” Fraser noted. “However, we cannot predict who will or will not experience depression in the future from the data. Importantly, fitness is something that most individuals can improve and maintain through regular participation in physical activity and exercise.”
The authors point to several possible biological pathways that might help explain why fitter youths tend to experience less depression in adulthood, noting that aerobic exercise is thought to promote the release of endorphins and brain-derived neurotrophic factor, a protein that supports the growth and repair of neurons, while helping regulate inflammation and the stress hormone cortisol. Because the association persisted even after accounting for how much exercise the children reported doing in 1985, the authors note that psychological and social pathways may also contribute, as fitter youths may build stronger self-esteem, better body image, and wider social support networks.
As with all research, there are some caveats to consider. Early fitness may act as a broader marker for lifelong activity habits, health behaviors, socioeconomic conditions, and shared genetic factors that were not measured in this cohort. In addition, tracking participants over more than three decades involved substantial attrition, with the final analysis including up to 1,080 of the original 8,498 children, or about one in eight. The cycling and handgrip tests were also only administered to 9-, 12-, and 15-year-olds in 1985, leaving a smaller sample of 437 participants and 75 depression cases for those specific analyses.
“The biggest misconception would be to conclude that fitness prevents depression or that low fitness causes depression,” Fraser emphasized. “As this was an observational study, no cause and effect was established.”
“Fitness may be one contributing factor among biological, psychological, social, and other influences on mental health,” she said. “We also do not want to overlook the importance of other aspects of physical fitness, which provide many health and well-being benefits even though they were not as consistently associated with depression in this study.”
Another limitation is that adult participants had to recall the onset of depressive episodes across more than three decades, which can introduce memory errors despite the use of a rigorous clinical diagnostic interview. Field tests such as the one-mile run can also be affected by a child’s pacing and motivation on testing day rather than pure physiological capacity. Future studies will need to explore why the link between muscle strength and depression shifts between adolescence and middle age, and establish practical fitness benchmarks for youth health programs.
“Further research is needed to determine whether the observed associations between childhood and adolescent fitness and later depression are causal and to better understand the biological, psychological, and social mechanisms that may underpin these relationships,” Fraser concluded.
“Future studies using different research designs could help determine whether improving fitness in childhood can reduce the risk of depression later in life and, if so, why,” Joshanloo said.
The study, “The long run: Fitness during childhood and adolescence and its association with adult depression,” was authored by Kylie J. Smith, Costan G. Magnussen, Cristina Cadenas-Sanchez, Grant R. Tomkinson, Leigh Blizzard, Kristy Sanderson, Terence Dwyer, Alison J. Venn, and Brooklyn J. Fraser.