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8/6/2019 Physical Activity and Depression: With a Attention to Research Among Adolescent Girls
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Running Head: PHYSICAL ACTIVITY AND DEPRESSION 1
Physical Activity and Depression:
With Attention to Research Among Adolescent Girls
Margae Knox
University of California, Berkeley
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PHYSICAL ACTIVITY AND DEPRESSION 3
Physical Activity and Depression: With Attention to Research Among Adolescent Girls
Introduction
Depression Prevalence and Characteristics
Major depressive disorder is strikingly common. It is characterized by the presence of
five or more of the following symptoms: depressed mood, diminished interest or pleasure in all
or most activities, significant weight loss or weight gain with change in appetite, difficulty
sleeping or excessive sleeping, slow movement observed by others, fatigue or loss of energy,
feelings of worthlessness or excessive guilt, diminished ability to concentrate or make decisions,
and recurrent thoughts of death. Symptoms occur most days during the past two weeks and areunaccounted for by other circumstances such as loss of a loved one: (American Psychiatric
Association Task Force on DSM-IV, 2000). In a national survey, 17.1% of people ages 15-54 in
the United States indicated they had experienced a lifetime prevalence of depression; 4.9% of
respondents indicated they currently were experiencing depression (Blazer, Kessler, McGonagle,
& Swartz, 1994). An updated version of this survey, quoted by the CDC ( Morbidity and
Mortality Weekly Report, 2010), found a 16.2% lifetime prevalence for major depression with a
6.6% 12-month prevalence (Kessler et al., 2003).
“Mental illness is not a trivial issue […] rather, it is as common as high blood pressure
and much more common than heart attack and stroke” (Biddle & Mutrie, 2001, p. 205).
According the World Health Organization, depression is the fourth leading contributor the global
burden of disease and the second leading cause of disability among 15-44 year olds (2011).
Worldwide, depression is about two times more prevalent in women compared to men. Research
indicates the higher female prevalence is due to greater first-onset among women, not differential
length, recurrence frequency, or help seeking patterns.
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PHYSICAL ACTIVITY AND DEPRESSION 4
Because depression typically emerges in adolescence and can recur throughout life, it is
important to better understand symptoms, prevention and treatments among this age group
(Kessler, 2003). According to Birmaher et al.’s review, the prevalence of current depression in
children varies between 0.4% and 2.5% but in adolescence the range increases to between 0.4%
and 8.3% (1996). During adolescence, the estimate of lifetime depression prevalence increases to
between 15% and 20%, comparable to proportions found in the adult population. (Birmaher et
al., 1996; Blazer et al., 1994; Kessler et al., 2003). The Oregon Adolescent Depression Project, a
survey of 1709 high school students ages 14 to 18, found a 2.9% point prevalence and 20.4%
lifetime prevalence the first year. The year’s incidence—the percentage of subjects not initiallydepressed that developed depression—was 7.8%. (Lewinsohn, Rohde, & Seeley, 1998). Though
boys and girls experience nearly equal levels of depression in childhood, beginning about age
thirteen depression levels in girls significantly increase compared to boys and soon reach the
two-to-one ratio observed in adulthood (Twenge & Nolen-Hoeksema, 2002). Female gender is a
key risk factor for both earlier onset and greater prevalence of depression.
Physical Activity and Depression Correlations
Studies in adult populations typically find an inverse relationship between physical
activity levels and depression. Physical activity is any bodily movement that engages muscles
and uses more energy than when resting. Physical activity, in contrast to exercise, need not be
planned or structured (National Heart, Lung, and Blood Institute, May 2009). The American
College of Sports Medicine claims “Regular physical activity is associated with improved levels
of psychological well being,” and assigns this statement an evidence category A/B, indicating
overwhelming/substantial evidence with strong, but sometimes inconsistent evidence from
randomized control trials and observational studies (Chodzko-Zajko WJ et al., 2009). Physical
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PHYSICAL ACTIVITY AND DEPRESSION 5
activity and depression is a growing area of study and an understanding of the relationship
between physical activity and depression is continually improving.
The first large prospective study that pointed to physical inactivity as a risk factor for
depression symptoms was the Epidemiologic Follow Up Study (1982-1984) to the first National
Health and Nutrition Examination Survey (NHANES I). Self reported data from 1,900 healthy
subjects, 25-77 years old, revealed a cross-sectional association between little or no physical
activity and greater depression symptoms. The study’s analysis, which excluding women
depressed at baseline, found that initial physical activity levels were an independent predictor of
depression at follow-up eight years later. Women who participated in little or no recreationalactivity were two times more likely than women with much or moderate physical activity to
develop depression symptoms at follow up (Farmer et al., 1988.) In a foundational meta-analysis
of physical activity and depression studies, North, McCullagh, and Tran examined 80
experimental studies (1990). The effect sizes calculated for each individual study ranged from
-3.88 to 2.05. But overall, a statistically significant mean effect size of -.53 was calculated,
indicating that depression levels among exercise treated groups were about one-half a standard
deviation lower than control groups (North et al., 1990). While these meta-analysis findings are
noteworthy they should be observed cautiously due to concerns about the methodological quality
of included studies and whether statistically combining the effect sizes is appropriate given the
large variety of study designs and populations (Biddle & Mutrie, 2001, p. 212).
Nevertheless, the literature to date provides a credible link between physical activity and
depression outcomes. The nine classic epidemiology criteria for determining whether an
association exists between an illness and an environmental condition are strength of association,
consistency of observed association, specificity of effect, temporal sequencing, dose-response
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PHYSICAL ACTIVITY AND DEPRESSION 6
relationship, biological plausibility, coherence with current understanding, experimental support,
and existence of analogous associations (Hill, 1965). The physical activity and depression
association generally meets seven these nine criteria, the exceptions being a dose-response
relationship and specificity (Biddle & Mutrie, 2001, pp 217-219).
Physical Activity and Depression in Adolescents
Although the relationship between physical activity and depression is less studied in
adolescents than adults, there are noteworthy observations and experiments. Very broadly,
physical activity levels substantially drop during the adolescent years, the same age range where
depression increases. During school-age years, activity levels decline 2.7% per year in males and7.4% per year in females (Pate, Long, & Heath, 1994). Between the ages 12 to 21, physical
inactivity increases 10.4% in males and 11.2% in females while regular vigorous activity
decreases 28.6% in males and 36.0% in females (Caspersen, Pereira, & Curran, 2000). At the
same time, depression among adolescents increases from a childhood point prevalence of 0.4-
2.5% (Birmaher et al., 1996) to nearly an adult point prevalence of around 4.9% (Blazer et al.,
1994). In a review by Calfas and Taylor, nine out of eleven studies addressing depression had a
positive benefit relationship with physical activity (1994).
In general, studies that examine the relationship between physical activity and depression
in adolescents have mixed findings. A study in London involving 2,789 students in grades seven
and nine found that every additional hour of exercise per week was associated with an 8%
decreased odds of depressive symptoms. A follow up survey, which included 75% of the original
population, found a consistent trend, but failed to maintain a statistically significant association
(Rothon et al., 2010).
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PHYSICAL ACTIVITY AND DEPRESSION 7
One of the first experimental studies of aerobic exercise and depression in adolescents
was a 9-week trial conducted among 27 patients in a private psychiatric facility. A high attrition
rate resulted due to discharge from the facility. Only eleven subjects, four boys and seven girls,
completed the study. The treatment group received extra running/aerobic classes three times per
week while the control group participated in only the usual physical activity program at the
facility. Treated girls’ depression scores consistently decreased though treated boys’ depression
scores did not, but the measurements are too variable and the sample sizes too small to draw
meaningful conclusions (Brown et al., 1992). Overall, differences between treatment and control
groups were not statistically significant (Brown, Welsh, Labbe, Vitulli, & Kulkarni, 1992; Larun, Nordheim, Ekeland, Hagen, & Hein, 2009).
More recently, an analysis of physical activity and depression used information from the
TEENS (Teens Eating for Energy and Nutrition at School) study, a prospective survey that
annually assessed 4,595 total middle-school students between the start of seventh grade and the
conclusion of eighth grade. The study examined a correlation between Center for Epidemiologic
Study Depression (CES-D) scores and the question “Do you get some regular physical activity
outside of school? By regular we mean at least 3 times a week for at least 20 minutes at a time.”
Responses to this question ranged on a five-point scale, with five indicating “most of the time”
and one indicating “never”. A modest relationship emerged such that higher initial levels of
depression were associated with lower scores of physical activity and reductions in physical
activity over time were associated with increasing depression. Quantitatively, one standard
deviation change in the measurement for physical activity frequency was correlated an inverse
.25 standard deviation change in depression symptoms. (Motl, Birnbaum, Kubik, & Dishman,
2004). Alternatively, a survey of 727 adolescents in grades 7-12 found no significant association
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PHYSICAL ACTIVITY AND DEPRESSION 8
between accumulated duration of moderate to vigorous physical activity and severity of
depressive symptoms. A relationship between participation in sports or lessons and depression
severity was also considered, but only an association among boys and not among girls was found
(Desha, Ziviani, Nicholson, Martin, & Darnell, 2007). These various studies are informative but
limited, and the possible relationship between physical activity and depression in adolescents
still requires further exploration. Studies of physical activity depression among adolescent
females are particularly important because depression risk factors and outcomes among females
may differ compared to males.
Hypotheses
HPA Axis & Cortisol
A number of mechanisms could potentially contribute to or help explain a possible
relationship between physical activity and depression. The HPA—hypothalamic-pituitary-
adrenal—axis, which regulates cortisol secretion, is one possible mechanism. Approximately
50% of depressed patients exhibit a hyperactive HPA axis (Southwick, Vythilingam, & Charney,2005). The HPA axis begins with secretion of CRH—corticotrophin-releasing hormone—from
the hypothalamus. CRH in turn causes the anterior pituitary to release ACTH—
adrenocorticotropic hormone—which then stimulates cortisol production from the adrenal
glands. (Davies, Blakeley, Kidd, & McGeown, 2001) In acute, regulated amounts, cortisol is
responsible for desirable adaptive responses; it is “essential for optimal functioning of virtually
all tissues” (Davies et al., 2001). However, chronically high levels of cortisol are harmful to
physical and mental health (Southwick et al., 2005). There are several possible associations
between HPA activity and depression although researchers still do not fully comprehend this
complex relationship. Overall, more severe depressive symptoms are associated with increased
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PHYSICAL ACTIVITY AND DEPRESSION 9
secretion of cortisol, also known as hypercortisolism (Angold, 2003). Gold et al. claim that the
evidence suggests hypercortisolism in depressed people is due to a defect at or above the
hypothalamic level, but this hypothesized defect’s precise nature, including the direction of
causation, is unknown (Gold, Goodwin, & Chrousos, 1988). It is also possible that
hypercortisolism is primarily just an indicator of stressful life events that lead to depression.
Further, hypercortisolism is not present in every case of depression and it is rarely observed in
children. Though depressed adolescents typically do not exhibit constant hypercortisolaemia,
they do often have elevated cortisol levels before sleep onset, a time when the HPA axis is
usually more at rest (Angold, 2003).Exercise may improve depression in part by regulating the HPA axis response to stress
(Brosse, Sheets, Lett, & Blumenthal, 2002). Very generally, about half of studies reviewed by
Gerber and Puhse indicated that people with high exercise levels exhibit fewer health problems
when exposed to stress (2009). More specifically, a study comparing sedentary persons to
moderately and highly trained athletes examined subjects’ HPA axis activation, measured by
plasma ACTH after weekly treadmill exercises. Exercises were performed at 50% VO2
maximum the first session, 70% the second, then 90% the final session. Trained and sedentary
subjects had equal HPA axis activation at equal percentages of maximum oxygen uptake levels,
but trained subjects required a greater absolute amount of oxygen consumption to equally
activate the HPA axis (Luger et al., 1987). However, it is not possible to say whether the
athletes’ lower HPA activity at equal absolute workloads generalizes to lower HPA activity
given equal life stressors. Additionally, the specific HPA changes in response to physical
training are uncertain. A study of trained male athletes compared to moderately athletic males
found elevated plasma ACTH levels, but no difference in cortisol levels was found in the trained
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PHYSICAL ACTIVITY AND DEPRESSION 10
athletes, suggesting that exercise training may lessen adrenal response to ACTH (Wittert,
Livesey, Espiner, & Donald, 1996). It is still unknown how these findings correspond with
depression levels and whether findings can be generalized to adolescents.
Neurotransmitters
Neurotransmitters are a second biological pathway related to depression. Most studies
have focused on seratonin and norepinephrine, the first neurotransmitters linked to mood. In the
1950’s, a connection between neurotransmitters and mood was serendipitously discovered when
a hypertension treatment, reserpine, led to depression in about fifteen percent of treated patients.
Investigation found that reserpine depletes norepinephrine and the serotonin precursor 5-HT bydamaging intracellular storage. The damage also makes norepinephrin and 5-HT degradation
more likely. Soon after this discovery, elevated mood was observed in isoniazid-treated
tuberculosis patients. Isoniazid inhibits norepinephrine and 5-HT degradation. Together, these
findings led to the hypothesis that higher monoamines levels are related to increased mood
(Dunn & Dishman, 1991, p. 57).
Supporting this neurotransmitter hypothesis, depressed patients typically have low levels
of the main serotonin metabolite 5-HIAA in measurements from cerebral spinal fluid.
Pharmacologic studies initially focused on drugs inhibiting norepinephrine uptake, and
simultaneously inhibited serotonin uptake, in order to elevate neurotransmitter levels. Research
efforts have since shifted from norephinephrine to serotonin since it has been shown that drugs
such as Prozac that only inhibit serotonin uptake are equally effective (Ganong, 2005, p. 262-
263). While original hypotheses about neurotransmitter mechanisms have been revised several
times as research has advanced, a consensus remains that monoamines are related to depression
(Dunn & Dishman, 1991, p. 57; Morgan, 1985).
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PHYSICAL ACTIVITY AND DEPRESSION 11
Theoretically, like pharmacologic treatments for depression, exercise could increase
levels of brain norepinephrine and 5-HT; but this assumption is mostly speculative (Morgan,
1985). Evidence linking neurotransmitters and physical activity is limited. Whole brain
norepinephrine has been found to decrease with acute exercise episodes but increase in response
to repeated, chronic exercise (Dunn & Dishman, 1991, p. 69). In both trained animals and
humans, short-term physical activity increases blood concentrations of tryptophan, a building
block of serotonin (Chaoulaoff, 1997, p. 182). Acute physical activity may also increase
synthesis and/or release of 5-HT but conclusive statements cannot be made without more
research (Chaouloff, 1997, p. 188). Exercise studies in animal models of depression couldtremendously help to further understanding of interactions between depression-like behavior,
exercise and neurotransmitters (Dunn & Dishman, 1991). One animal model experiment found
that compared to sedentary mice, mice that were allowed activity wheel exercise had statistically
significant lower escape latency after uncontrollable foot shocks, suggesting exercise might
buffer depression in response to stress. This experiment also showed statistically significant
higher levels of norepinephrine in the brain’s locus coeruleus among activity wheel mice
compared to sedentary mice (Dishman et al., 1997).
It is unclear how neurotransmitters interact with the HPA axis and hormone systems.
Researchers have suggested that norepinephrine produces both stimulatory and inhibitory effects
on the HPA axis. Both of these contrasting propositions could be true. Norepinephrine likely
produces different effects at different levels of the HPA axis (Dunn & Dishman, 1991, p. 66).
Meanwhile, one study concluded that HPA hyperactivity does not seem related to serotonin
dysfunction (Molcrani, Duval, Crocq, Bailey, & Macher, 1997).
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PHYSICAL ACTIVITY AND DEPRESSION 12
Neurotransmitters and the HPA axis also interact with steroid hormones in a delicately
balanced manner. For example, ACTH from the pituitary stimulates adrenal androgen secretion
(Davies et al., 2001, p. 441). And, higher levels of estrogen at puberty can alter neurotransmitter
sensitivity (Steiner, Dunn, & Born, 2003). It is still unclear how the dramatic hormone changes
associated with menarche might contribute to the increases in depression incidence observed at
about the same time. Steiner et al. propose that the hormonal changes associated with menarche
require the HPA to mature to become sensitive to new feedback mechanisms. This adjustment
period may increase the vulnerability of the HPA axis to psychosocial stress (2003). Better
identification of these interactions could be very influential for the evaluation and treatment of depression in adolescent girls.
Sleep
Sleep abnormalities are both a symptom of depression and a risk factor. About 90% of
depressed patients report sleep disturbances (Mendelson, Gillin, & Wyatt, 1977). In a
prospective study, among those that developed major depression, the odds of insomnia were 39.9
times the odds of insomnia among those that did not develop depression (Ford & Kamerow,
1989). Studies typically define a sleep cycle as four progressively deeper stages of slow-wave
sleep that then regress to the original stage and are followed by the very light, rapid eye
movement (REM) stage (Driver & Taylor, 1996). Subjects with primary depression often exhibit
a shortened REM latency, i.e., a reduced time period until REM sleep is initiated (Kupfer, 1976).
Additionally, several but not all sources suggest that an increased REM latency is correlated with
depression remission. Increased REM latency is observed with many antidepressant medications
(Riemann Berger, & Voderholzer, 2001). In a review of studies among children and adolescents,
depressed subjects compared to controls exhibited statistically significant shortened REM
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PHYSICAL ACTIVITY AND DEPRESSION 13
latency in seven of thirteen sleep studies. Five studies showed that depressed subjects had
statistically significant increases in sleep onset latency, the time to fall asleep. There were no
statistically significant differences in slow wave sleep measures (Riemann et al., 2001).
Exercise may impact sleep a number of ways. In a random sample of 200 middle-aged
men and women, one third felt that exercise positively impacts sleep, with the most common
reports including improved ease falling asleep, deepness of sleep, sense of well-being and
morning wakefulness (Vuori, Urponen, Hasan, & Partinen, 1988). The extent to which research
supports these common perceptions is mixed. In general, morning exercise has little affect on
sleep, while afternoon exercise increases slow-wave sleep, delays onset of REM, and shortensthe REM stage (Driver & Taylor, 1996; Youngstedt, O'Connor, & Dishman, 1997). Kubitz et al’s
meta-analysis calculated effect sizes for both acute and chronic exercise studies in order to
determine the immediate effects of exercise on sleep and the effects of long-term exercise on
sleep. The overall meta-analysis did not account for the time of day exercise was conducted, but
in both acute and chronic exercise studies exercising individuals fell asleep faster and slept
slightly longer and deeper (1996). In one of few adolescent studies of exercise and sleep Brand et
al. compared high-exercising and low-exercising adolescents, with mean exercise durations of
8.5 and 2.5 hours per week respectively. The study found that high exercisers had more slow-
wave sleep, less light and REM sleep, and lower depressive scores (2010).
Methodological concerns of most sleep studies include small sample sizes. A small
sample size reduces the statistical power, the ability to ascertain whether observed effects are
real (Kubitz et al., 1996). Studies of exercise’s effect on sleep typically only include samples
with good-sleepers so that exercise effects among populations with sleep disturbances, including
many cases of depression, remains undetermined (Kubitz et al., 1996; Youngstedt et al., 1997). It
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PHYSICAL ACTIVITY AND DEPRESSION 14
is also unclear whether study results from adult populations can be generalized to adolescents; it
is likely that adolescent sleep patterns and responses to exercise significantly differ (Dahl et al.,
1996). Additionally, further exploration might examine whether sleep abnormalities are related
to endocrine abnormalities in depression (Riemann et al., 2001). Observations of HPA-axis
change just before and just after sleep onset supports a connection between hormones, sleep and
depression (Dahl et al., 1996)
Self-Esteem
While biological mechanisms are critical for explaining physical activity’s potential
antidepressant effects, cognitive explanations such as self-esteem are also worthwhileconsiderations. High self-esteem, especially in girls, appears to be an important element of good
mental and physical health (Park, 2003). Eckeland et al. discuss twenty-three studies of exercise
interventions on self-esteem in a literature review that was subsequently elaborated on in a report
by the Cochrane Collaboration. Meta-analysis of twelve of the twenty-three studies revealed a
small, statistically significant effect on self-esteem in favor of the exercise interventions, with
intervention and control groups differing by about a ten percent (Ekeland, Heian, Hagen, Abbott,
& Nordheim, 2004; Ekeland, Heian, & Hagen, 2005).
Although a direct relationship between actual physical fitness and self-esteem is
uncommon, a consistent relationship exists between perceptions of physical fitness and self-
esteem. Accordingly, intervention studies find that improved perceptions of physical fitness are
more strongly correlated to self-esteem than actual physical fitness improvement. Further, self-
esteem often improves before fitness effects have had time to take place (Sonstroem, 1984). A
study that compared self-esteem measures between a running group, a weight-training group, and
a delayed-treatment control group also supports this idea. Both the aerobic and weight-training
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PHYSICAL ACTIVITY AND DEPRESSION 15
groups experienced significant self-esteem improvements compared to the control group. The
aerobic and weight training subjects also both perceived themselves as having improved fitness,
but neither group showed improved treadmill test performance (Ossip-Klein et al., 1989, p. 160).
Another relevant study compared a ten-week exercise program divided into two exercise groups
of 24 subjects each. In one group instructors emphasized anticipated improvements in both
aerobic capacity and psychological well being, and in the other group instructors were equally
enthusiastic but only focused on the exercise program’s biological aspects. Both groups
experienced improved self-esteem, but the group primed by instructors to expect psychological
improvements had significantly greater scores (Desharnais, Jobin, Cote, & Levesque, 1993)During the developmental stage of adolescence, physical activity success may be
particularly meaningful for improving self-esteem (Calfas & Taylor, 1994). Physical Activity
Epidemiology lists a loss of self-esteem as one of several etiologic factors of depression, but
studies have not identified precisely how self-esteem contributes to the lower rates of depressive
symptoms in physically active people (Dishman, Washburn, & Heath, 2004, p. 311 & 327).
Theoretically, physical activity will enact self-esteem improvements through a cycle of positive
feedback between the skill development hypothesis of self-esteem and the self-enhancement
hypothesis. The skill development hypothesis proposes that successful experiences make an
individual feel good about herself, and the self-enhancement hypothesis is the idea an individual
will act based on her perception of herself. As a person perceives successes from time spent in
physical activity, she will continue to pursue those activities. And, as physical activity makes her
feel good about herself, self-esteem is continually enhanced and the cycle perpetuated
(Sonstroem, 1997, p. 128-129). Additional features of physical activity that possibly contribute
to improved self-esteem include: increased sense of competence, skill mastery, goal
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PHYSICAL ACTIVITY AND DEPRESSION 16
achievement, feelings of somatic well-being, social experiences (Sonstroem, 1997, p.129),
favorable comments by friends, and distraction from stressful stimuli (Morgan, 1985).
Most studies that examine a relationship between physical activity and self esteem focus
on the relatively stable, one-dimensional global self-esteem, which, according to Sonstroem, has
hindered self-esteem research. More recent models of self-esteem advance a hierarchical nature
of self-esteem: the global self-esteem is comprised of several domain-specific esteems and sub-
domains (Sonstroem, 1997). For example, physical self-esteem is a domain of global self-esteem
and associated sub-domains include physical strength, attractive body and sports competence
(McAuley, Mihalko, & Bane, 1997). While global self-esteem relates to overall psychologicalwell-being, domain specific esteem is more predictive of actual performance. This distinction is
important because it explains why self-esteem studies often report weaker associations than
might be expected (Rosenberg, Schooler, Schoenbach, & Rosenberg, 1995) McAuley’s analysis
of physical fitness and self-efficacy in a 20-week exercise program among middle-aged adults
reflects how the domain level influences self-esteem measures. Self-efficacy change was greatest
at the sub domain level for physical condition, mid-level at the physical esteem domain level,
and least at the global level. As understanding of how physical activity and self-esteem interact
develops, researchers also gain understanding toward reducing depression (McAuley et al.,
1997).
Methods
Studies for closer review to assess the relationship between physical activity and
depression in adolescent girls were gathered through a PubMed search. The search term
“physical activity and depression” was used with the limits “Female” and “Adolescent: 13-18
years.” The search details generated were: “(("motor activity"[MeSH Terms] OR ("motor"[All
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PHYSICAL ACTIVITY AND DEPRESSION 17
Fields] AND "activity"[All Fields]) OR "motor activity"[All Fields] OR ("physical"[All Fields]
AND "activity"[All Fields]) OR "physical activity"[All Fields]) AND ("depressive
disorder"[MeSH Terms] OR ("depressive"[All Fields] AND "disorder"[All Fields]) OR
"depressive disorder"[All Fields] OR "depression"[All Fields] OR "depression"[MeSH Terms]))
AND ("female"[MeSH Terms] AND "adolescent"[MeSH Terms])” 410 results were returned.
Articles were then browsed for titles that directly addressed the relationship between physical
activity and depression in an adolescent female population.
Results
Three studies from the PubMed search—a cross-sectional study, a prospective study, anda randomized control trial—met the criteria for this literature review, directly addressing the
relationship between physical activity and depression in an adolescent female population. The
search results also returned findings about depression and physical activity more generally,
including three studies described previously that examined a relationship between physical
activity and depression among both male and females (Brown et al., 1992; Desha LN et al.,
2007; Motl et al., 2004). In summary, significant relationships emerged between physical activity
and depression in two of the three studies discussed below. Each study acknowledges a
relationship between physical activity and depression could also reflect unmeasured factors
associated with physical activity such as social connections, skill-mastery, and distraction. Two
of the three studies assume a relationship in which physical activity impacts depression (Johnson
CC et al., 2008; Nabkasorn et al., 2006), but the relationship may also be bi-directional (Jerstad
SJ et al., 2010).
Study One
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PHYSICAL ACTIVITY AND DEPRESSION 18
Depressive Symptoms and Physical Activity in Adolescent Girls (Johnson CC et al.,
2008). The objective of this study was to evaluate the relationship between depressive symptoms
and physical activity in a geographically and ethnically diverse sample of sixth grade adolescent
girls. The study built on the National Heart, Lung, and Blood Institute’s TAAG (Trial of Activity
of Adolescent Girls) study, whose goal was to design and evaluate and intervention that would
reduce the physical activity decline in middle school girls by half. Each of six different field
centers—Universities of Arizona, Maryland, Minnesota, and South Carolina; San Diego State
University and Tulane University—collected data from six different schools, resulting in 36
geographic and ethnically diverse schools included in the study. Before schools in the TAAGstudy were randomized into treatment and control conditions, baseline measurements were made.
Sixty girls from each site were randomly selected to be recruited for the TAAG study and 1,721
(80%) agreed. Of these, 1,397 girls had complete measurements for all three variables required
in this study.
The three baseline measurements of special interest to the current study are the Center for
Epidemiology Study Depression scale (CES-D), MTI ActiGraph Accelerometer data, and the
3DPAR (3-Day Physical Activity Recall) survey. The CES-D scale is a twenty-item
questionnaire with responses ranging on a four-point scale from “rarely” to “almost always.” The
CES-D has been standardized, has high to acceptable internal validity, and is used extensively in
research with adolescents and adults. Although it is not a diagnostic tool, a score greater than 16
in adults and greater than 24 in adolescents has been used to signal depression. An accelerometer
is like a sophisticated pedometer to measure physical activity levels. An accelerometer is able to
detect acceleration and deceleration and record the time of day, providing data on the
vigorousness and intervals of physical activity. The 3DPAR is a self-report survey that asks
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PHYSICAL ACTIVITY AND DEPRESSION 19
participants to recall their activities for every thirty minutes over the past three days. The 3DPAR
has been validated against pedometer counts and accelerometer counts. Other measurements that
were noted and adjusted for in analysis include BMI and a questionnaire of demographics,
attitudes toward physical activity, social support, and barriers to physical activity.
This study generated both mixed-model linear and mixed-model logistic regressions
relating physical activity and CES-D. The linear model treated CES-D score as continuous
variable while the logistic regression model treated CES-D score as a binary variable based on a
cut of score of 24. The study separately analyzed nine categories of physical activity ranging
from sedentary to vigorous activity. Five of these categories came from the accelerometer datameasurements and four from the 3DPAR survey measurements. With the exception of sedentary
activity, neither linear nor logistic regressions revealed a relationship between physical activity
measures and CES-D scores. In the linear model, sedentary behavior measured by accelerometry
indicated a modest, statistically significant inverse correlation with depression; i.e., every
additional minute of sedentary behavior yielded a .00987-point decrease in CES-D scores
suggesting very slightly improved depression. A two standard deviation increase in sedentary
behavior in this sample would predict a 1.35-point decline in CES-D scores. However the
authors acknowledged that the inverse relationship between sedentary behavior and depression
might be a statistical anomaly, an artifact of the fact sedentary behavior was high while CES-D
scores generally were not.
One of this study’s strengths was the combination of a more objective accelerometry
measurement for physical activity in addition to a self-report method. In combination, these
methods should have derived highly reliable physical activity measurements. The study reported
that on average the sample of girls engaged in an average of less than 24 minutes per day of
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PHYSICAL ACTIVITY AND DEPRESSION 20
moderate and six minutes per day of vigorous physical activity. A review by Pate et al. concurred
that the majority of adolescent females were not meeting the guidelines for moderate to vigorous
physical activity, but differed with this study by suggesting that on average adolescents exercised
one hour a day, they just failed to do so three or more days a week (Pate et al., 1994). Perhaps
results differed because, in contrast to the studies reviewed by Pate et al, this study more
rigorously measured and more specifically classified physical activity.
Study Two
Prospective Reciprocal Relations Between Physical Activity and Depression in
Female Adolescents (Jerstad SJ et al.). This study sought to prospectively examine therelationship between physical activity and adolescents in order to test whether physical activity
reduces risk for future escalations of depression or whether depression reduces future physical
activity. Of the girls recruited, ages eleven to fifteen, 496 girls (56%) agreed to participate. Each
year throughout the six-year follow-up period the girls completed a questionnaire, participated in
structured interviews and had their height and weight measured. In addition to depression and
physical activity, other covariates of interest in this study were body dissatisfaction, bulimic
symptoms, social support, and body mass.
Depression was measured from structured interviews using the Schedule for Affective
Disorders and Schizophrenia for School-Age Children, a tool to assess whether subjects met the
Diagnostic and Statistical Manual of Mental Disorder criteria for major depressive disorder or
minor depression on a monthly basis over the past year. Physical activity was assessed with a
modified version of the Past Year Activity Scale, where subjects indicated the number of
activities they had participated in ten or more times during the past year.
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PHYSICAL ACTIVITY AND DEPRESSION 21
Baseline physical activity predicted less depression over time. For each additional
physical activity participated in, the relative risk of later depression symptoms decreased one
percent; the relative risk of later minor or major depression decreased 8% and the relative risk for
later major depression decreased 16%. At the same time, the presence of depression symptoms
predicted reduced physical activity. Major depression decreased the likelihood of participating
on one additional physical activity the next year by 35% and minor depression decreased the
likelihood by 18%. All predictive effects adjusted for baseline depression and measured
covariates. Predictive effects were also all statistically significant.
Study Three
Effects of physical exercise on depression, neuroendocrine stress hormones and
physiological fitness in adolescent females with depressive symptoms (Nabkasorn et al.,
2006). This study attempted to address the current lack of experimental studies examining
psychological and physiological changes among depressed adolescents in response to physical
activity. The study used a crossover experimental design to evaluate the effects of an eight-week
exercise regimen compared to eight weeks of usual activity. Two hundred sixty six female
volunteers aged 18-20 were recruited for the study and evaluated for depressive symptoms.
Sixty-three participants presented mild to moderate depressive symptoms and did not meet the
exclusion criteria. Exclusion criteria included previously taken antidepressant medication,
symptoms of illness limiting physical activity, or engaged in regular, vigorous sports activity
during the prior six months. Fifty-nine participants agreed to participate. Originally, twenty-eight
subjects began with a physical activity while 31 subjects continued with their daily usual routine
as non-exercise controls. The physical activity program involved 50-minute group jogging
sessions performed at less than 50% maximal heart rate five days per week. After eight weeks,
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PHYSICAL ACTIVITY AND DEPRESSION 22
the two groups switched roles. In the end 49 subjects—21 in the training first group and 28 in the
usual activity first group—completed the trial as prescribed and were included in analysis.
Every four weeks subjects completed the Center for Epidemiologic Study of Depression
(CES-D) scale, the main outcome measure in this study. At baseline and at eight-week intervals,
upon the conclusion of their respective exercise or usual activity period, subjects collected
separate 24-hour urine specimens to measure urinary cortisol and urinary epinephrine.
Specimens were sent to a laboratory where urinary cortisol was measured by radioimmunoassay
and urine epinephrine was measured by liquid chromatography. Additionally, at baseline and
eight-week intervals, measurements were made of lung capacity, heart rate and peak oxygenintake. Lung capacity was measured with a spirometer. Heart rate was measured while subjects
were seated for five minutes during the rest periods of an endurance test performed according to
the multistage YMCA submaximal exercise test protocol. Peak oxygen was estimated on the
basis of the heart rate increments to workloads during the endurance test.
In the training-first group CES-D scores significantly decreased during the first phase,
indicating improved depression, and then scores gradually rose during the regular daily activity
in the second phase. At the end of the second phase, however, CES-D scores continued to remain
significantly below baseline. The regular-daily-activity-first group had no significant changes in
any measurement during the first phase but significantly decreased CES-D scores during the
following exercise-training phase. Additional changes following the exercise training phase
included lower 24-hr urinary cortisol and norepinephrine secretions, lower heart rate at rest,
increased lung capacity, and increased peak oxygen uptake. No changes occurred following the
daily activity phase. Mean body weight did not significantly change during either phase.
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PHYSICAL ACTIVITY AND DEPRESSION 23
Discussion
One of the challenges facing studies that examine physical activity and depression are the
limitations of physical activity and depression measurements. Both physical activity and
depression measurements regularly employ self-reported indicators such as surveys, which may
be inconsistent or unreliable. This is particularly true of surveys that are unique to a study and
have not been validated. Additionally, it is often difficult for surveys to fully capture the variable
of interest. For example, a physical activity survey that asks participants to rank their activity
levels from low to high cannot actually assess the actual number of minutes spent in physical
activity or the level of physical intensity.
Of the three studies only Johnson et. al., which collected accelerometry data, used an
objective physical activity measurement. This study did not find a relationship between physical
activity and depression. However it is possible that by dividing the physical activity data so
extensively any potential relationship between physical activity and depression was dampened.
Had measurements been analyzed as an accumulation as in other studies, a slight relation with
depression might have emerged. Although, like the relationship observed with sedentary
behavior, the potential relationship between physical activity and depression would likely be
modest and could also possibly be just an artifact of statistics.
The lack of a relationship between physical activity and depression demonstrated in this
study could also be due to many dependent variables that this study did not account for. This
study was thoughtfully designed, rigorously measuring physical activity, and even attempting to
adjust for factors associated with physical activity levels such as attitudes and social
environment. However, it is impossible to entirely account for activity factors that might
exacerbate or alleviate depression. For example, sedentary behavior might have shown a
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PHYSICAL ACTIVITY AND DEPRESSION 24
correlation with improved depression because sedentary time was spent with an engaging book
or sitting down to a pleasant family dinner. Although findings from cross-sectional study designs
like this one are interesting, they are also limited because they cannot assess temporality or make
causal inferences. Longer-term and experimental designs will help to expand understanding of
the relationship between physical activity and depression.
Jerstad et al. expanded understanding of the relationship between physical activity and
depression by employing a prospective study design, which can give an indication of
temporality. Jerstad et al.’s results suggest both that participation in physical activities can be
protective against depressive symptoms and that depressive symptoms decrease the probabilityof participation in physical activities. As acknowledged in Johnson et al. and other studies,
several variables likely play a role in the relationship between physical activity and depression.
Jerstad et al. adjusted for four factors—body dissatisfaction, bulimic symptoms, social support,
and body mass—and still observed a modest but significant bidirectional relationship. However,
conclusions could be strengthened by using measures that assessed actual time spent in physical
activity levels and average amounts of energy expenditure, not just a measure of participation in
certain activities. It could be that some subjects are very active, but participate in few distinct
activities. Or in contrast, some subjects might dabble in several activities without exerting much
effort at any one.
A randomized control trial is considered the gold standard of scientific studies. In
Nabaksorn et al.’s randomized control trial a crossover design a cross-over design was used,
which has the advantage of potentially counterbalancing errors in randomization by exposing
both groups to treatment and control conditions. However, a drawback of crossover design is that
residual effects of the first phase may influence results in the second phase (Gordis, 2004, pp
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PHYSICAL ACTIVITY AND DEPRESSION 25
140). One weakness of this study is that several subjects were not included in the final study
analysis. Five subjects dropped out and five subjects that were excluded because they failed to
maintain usual physical activity levels during the non-exercise phase. This 17% non-completion
rate but could have influenced results if data from those not included were systematically
different than those that properly completed the trial. For example, perhaps the low motivation of
the five-drop outs made them resistant to potential depression changes in response to physical
activity. It would also be interesting to find out how allowing subjects to participate that were not
included due to the exclusion criteria or changing the CES-D cut off score for inclusion would
have affected results.
Conclusions
Potential of Physical Activity as Treatment and Prevention for Depression
Research suggests that physical activity may be useful in treating depression, but
methodological weaknesses limit conclusions. Common weaknesses include small sample sizes,
inadequate blinding, and lack of intention-to-treat analysis (Lawlor & Hopker, 2001). Additionalconcern arises due to the limited external validity of depression studies. Exclusion criteria often
include previous medication use or experience with therapy and co-morbid disorders such as
anxiety and substance abuse, which disqualifies a large proportion of depressed outpatients
(Klein et al., 1985; Lawlor & Hopker, 2001).
One of the earliest studies considering physical activity as depression treatment compared
a running group to two psychotherapy treatments, one psychotherapy treatment time-limited and
the other time-unlimited. The authors concluded that running was at least as effective as
psychotherapy in alleviating moderate depression. However, the study design does contain
factors that may have influenced results. For example, psychotherapists were relatively
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PHYSICAL ACTIVITY AND DEPRESSION 26
inexperienced compared to the running therapist and subjects in the running group spent more
time in treatment (Greist et al., 1979). Since then, four studies among depressed patients
comparing physical activity with cognitive therapy, a specific type of psychotherapy, have been
conducted and were meta-analyzed in a review by Lawlor & Hopker (2001). Overall, these four
studies showed a -0.3 standardized mean difference effect size for depression treated with
physical activity compared to cognitive therapy, suggesting slightly greater depression
improvement from physical activity. But the mean difference 95% confidence interval ranged
from -0.7 to 0.1, indicating neither treatment is significantly more effective than the other
(Lawlor & Hopker, 2001).The relative effectiveness of physical activity compared to medication treatments are also
of interest. One study explored physical activity compared to the anti-depressant medication
sertralin (Zoloft®) by dividing102 subjects into four categories: a three-times-per-week,
supervised group setting exercise; a prescription for equivalent home-based, individual exercise;
sertralin; and a placebo pill. Initially researchers faced ethical concerns about assigning subjects
to a placebo treatment known to be less effective. However it is also known that depression is a
condition highly influenced by patient beliefs, and in a previous study where a placebo group
was not included the researchers results were met with skepticism. After sixteen weeks, 45% of
supervised exercise subjects, 40% of home-based exercise subjects, 47% of sertralin subjects,
and 31% of placebo subjects achieved remission. Again, the results suggest but cannot
definitively conclude that exercise is effective for treating depression. Also, as with
psychotherapy, effects of exercise treatments compared to medication were not significantly
different. The adjusted odds ratio of remission among the three active treatments compared with
placebo was 2.0, with a 95% confidence interval of .96 to 4.2. (Blumenthol et al., 2007). To
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PHYSICAL ACTIVITY AND DEPRESSION 27
better understand the long-term effects of exercise as a potential depression treatment,
researchers followed-up six months after a different four-month study. The study, compared an
exercise treatment, a sertralin treatment, and a combined treatment. During the initial four
months depression improvements between groups were comparable, though at follow-up
continued exercise helped to prevent depression relapse. The odds of classification as depressed
at follow-up decreased 50% with every additional 50 minutes of exercise reported per week
(Babyak et al., 2000).
It also would be clinically useful to know the potential effectiveness of physical activity
as adjunct treatment. A study to examine exercise as an adjunct treatment to counselingcompared three groups: a running program, cognitive based counseling, and engagement with
both programs. Similar to previous studies comparing only running and counseling, all three
treatments reduced depression but were not significantly different from each other (Fremont J &
Craighead LW, 1987). Exercise has also been considered as an adjunct to pharmacological
treatment. In study with thirty female patients, a control group of twenty subjects receiving
pharmacological treatment was compared with ten subjects receiving physical activity training in
addition to the pharmacological treatment. Significantly improved depression measures were
found in the group treated with physical activity as an adjunct. Depression measures were
improved, but did not reach statistical significance in the control group (Pilu A et al., 2007).
These results suggest physical activity is a good candidate for use as adjunct depression
treatment, but studies with larger samples and greater control comparisons are needed to confirm
this conclusion.
Determinations of physical activity’s efficacy may vary upon whether experts consider
subthreshold depressive symptoms—those that do not reach a level for clinical diagnosis—to be
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PHYSICAL ACTIVITY AND DEPRESSION 28
part of a spectrum of depressive disorders or distinct from clinical depression. Based on
Lewinsohn et al.’s analysis, depression can be conceptualized as a continuum, with no unique
consequence upon crossing the threshold of symptoms for clinical diagnosis of depression
(2000). Demonstrating this concept, as depression increased among adolescents the risk of a
substance use disorder within five years also increased, a relationship that held even among
subthreshold depressive symptoms. While no scientific consensus about subthreshold symptoms
currently exists, treatment of persistent subthreshold symptoms following a stepped-care model
of least costly and least aggressive treatments could be very beneficial for prevention of future,
more severe depression (Lewinsohn, Solomon, Seeley, & Zeiss, 2000).Physical activity could certainly serve as a free or little-cost prevention and treatment
strategy for people with subthreshold depressive symptoms and diagnosed depression. Greist et
al. calculate that running treatment compared to psychotherapy was four times more cost
effective in their clinic, where expenses totaled $115 for the running treatment compared to $500
for equally effective psychotherapy (1979). Physical activity is also minimally aggressive. It has
no known side effects when performed in a controlled manner and has also been shown
beneficial for improving cardiovascular disease, diabetes, and bone health (Chodzko-Zajko et al.,
2009). Factors such as motivation, social support and time commitments should be considered in
order to ensure the patient is able to follow through with exercise recommendations. Should
patients be unable to fully meet recommendations, clinicians would not want to provoke a sense
of failure that might exacerbate depression. With encouragement and realism from clinicians,
physical activity prescriptions could be an important intervention for improving mental health
(Donaghy & Taylor, 2010).
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PHYSICAL ACTIVITY AND DEPRESSION 29
Future Research Directions
Depression in adolescents is currently understood primarily by applying results from
studies among adults. In fact, adolescent physiology and psychology is distinct in many ways.
More studies focusing specifically on adolescents, when first depression onset is greatest, could
provide a unique understanding of depression development and progression. Additional
adolescent studies would also provide a window to explore the protective effects of physical
activity by examining a time when depression risk dramatically increases (Kessler et al., 2003).
It may not be possible to prevent depression altogether but it is possible that long-term benefits
might result from delaying depression onset.Longer-term prospective-cohort studies and improved randomized control trials will add
validity and understanding to the field. Current studies are largely cross-sectional and cannot
assess temporality and causation. Prospective cohort studies would be particularly beneficial in
comparison to retrospective studies, which often involve difficulty distinguishing depression
first-onset from recurrences. Identification of first onset might help clarify both protective and
harmful risk factors (Kessler et al., 2003). Additionally, most trials are of short duration,
typically sixteen weeks or less. Yet depression is a long-term condition. The mean length of
depression in studies of children and adolescents is seven to nine months (Birmaher.et al., 1996).
Studies over greater periods of time will also add insight to potential relationships between
depression and physical activity.
Research that examines a joint effect of biology and environmental/social determinants is
also important. For example, the hypothalamic pituitary axis is an area of research where biology
and environment appear to be closely intertwined. Yet research that considers a joint effect from
biological and environmental determinants of physical activity and depression is still minimal.
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PHYSICAL ACTIVITY AND DEPRESSION 30
Future risk factor research should more clearly appreciate both biological and environmental
contributions (Kessler et al., 2003).
Depression is a highly prevalent and debilitating illness. Depression typically emerges in
adolescence and is particularly prevalent among females. Meanwhile, physical activity could
potentially relate to physical activity through numerous mechanisms, including factors not yet
researched. Better understanding of the biological and environmental relationships between
depression and physical activity interactions could give rise to influential public health
interventions and improvements.
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PHYSICAL ACTIVITY AND DEPRESSION 31
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